Programs & Examples On #Objectfactory

How to create JNDI context in Spring Boot with Embedded Tomcat Container

I recently had the requirement to use JNDI with an embedded Tomcat in Spring Boot.
Actual answers give some interesting hints to solve my task but it was not enough as probably not updated for Spring Boot 2.

Here is my contribution tested with Spring Boot 2.0.3.RELEASE.

Specifying a datasource available in the classpath at runtime

You have multiple choices :

  • using the DBCP 2 datasource (you don't want to use DBCP 1 that is outdated and less efficient).
  • using the Tomcat JDBC datasource.
  • using any other datasource : for example HikariCP.

If you don't specify anyone of them, with the default configuration the instantiation of the datasource will throw an exception :

Caused by: javax.naming.NamingException: Could not create resource factory instance
        at org.apache.naming.factory.ResourceFactory.getDefaultFactory(
        at org.apache.naming.factory.FactoryBase.getObjectInstance(
        at javax.naming.spi.NamingManager.getObjectInstance(
        at org.apache.naming.NamingContext.lookup(
        at org.apache.naming.NamingContext.lookup(
        at org.apache.naming.NamingContext.lookup(
        at org.apache.naming.NamingContext.lookup(
        at org.apache.naming.NamingContext.lookup(
        at org.apache.naming.NamingContext.lookup(
        at org.apache.naming.NamingContext.lookup(
        at org.apache.naming.NamingContext.lookup(
        at org.apache.naming.SelectorContext.lookup(
        at javax.naming.InitialContext.lookup(
        at org.springframework.jndi.JndiTemplate.lambda$lookup$0(
        at org.springframework.jndi.JndiTemplate.execute(
        at org.springframework.jndi.JndiTemplate.lookup(
        at org.springframework.jndi.JndiTemplate.lookup(
        at org.springframework.jndi.JndiLocatorSupport.lookup(
        at org.springframework.jndi.JndiObjectLocator.lookup(
        at org.springframework.jndi.JndiObjectTargetSource.getTarget(
        ... 39 common frames omitted
Caused by: java.lang.ClassNotFoundException: org.apache.tomcat.dbcp.dbcp2.BasicDataSourceFactory
        at java.lang.ClassLoader.loadClass(
        at sun.misc.Launcher$AppClassLoader.loadClass(
        at java.lang.ClassLoader.loadClass(
        at java.lang.Class.forName0(Native Method)
        at java.lang.Class.forName(
        at org.apache.naming.factory.ResourceFactory.getDefaultFactory(
        ... 58 common frames omitted

  • To use Apache JDBC datasource, you don't need to add any dependency but you have to change the default factory class to org.apache.tomcat.jdbc.pool.DataSourceFactory.
    You can do it in the resource declaration : resource.setProperty("factory", "org.apache.tomcat.jdbc.pool.DataSourceFactory"); I will explain below where add this line.

  • To use DBCP 2 datasource a dependency is required:

    <dependency> <groupId>org.apache.tomcat</groupId> <artifactId>tomcat-dbcp</artifactId> <version>8.5.4</version> </dependency>

Of course, adapt the artifact version according to your Spring Boot Tomcat embedded version.

  • To use HikariCP, add the required dependency if not already present in your configuration (it may be if you rely on persistence starters of Spring Boot) such as :

    <dependency> <groupId>com.zaxxer</groupId> <artifactId>HikariCP</artifactId> <version>3.1.0</version> </dependency>

and specify the factory that goes with in the resource declaration:

resource.setProperty("factory", "com.zaxxer.hikari.HikariJNDIFactory");

Datasource configuration/declaration

You have to customize the bean that creates the TomcatServletWebServerFactory instance.
Two things to do :

  • enabling the JNDI naming which is disabled by default

  • creating and add the JNDI resource(s) in the server context

For example with PostgreSQL and a DBCP 2 datasource, do that :

public TomcatServletWebServerFactory tomcatFactory() {
    return new TomcatServletWebServerFactory() {
        protected TomcatWebServer getTomcatWebServer(org.apache.catalina.startup.Tomcat tomcat) {
            return super.getTomcatWebServer(tomcat);

        protected void postProcessContext(Context context) {

            // context
            ContextResource resource = new ContextResource();
            resource.setProperty("driverClassName", "org.postgresql.Driver");

            resource.setProperty("url", "jdbc:postgresql://hostname:port/dbname");
            resource.setProperty("username", "username");
            resource.setProperty("password", "password");

Here the variants for Tomcat JDBC and HikariCP datasource.

In postProcessContext() set the factory property as explained early for Tomcat JDBC ds :

    protected void postProcessContext(Context context) {
        ContextResource resource = new ContextResource();       
        resource.setProperty("factory", "org.apache.tomcat.jdbc.pool.DataSourceFactory");

and for HikariCP :

    protected void postProcessContext(Context context) {
        ContextResource resource = new ContextResource();       
        resource.setProperty("factory", "com.zaxxer.hikari.HikariDataSource");

Using/Injecting the datasource

You should now be able to lookup the JNDI ressource anywhere by using a standard InitialContext instance :

InitialContext initialContext = new InitialContext();
DataSource datasource = (DataSource) initialContext.lookup("java:comp/env/jdbc/myJndiResource");

You can also use JndiObjectFactoryBean of Spring to lookup up the resource :

JndiObjectFactoryBean bean = new JndiObjectFactoryBean();
DataSource object = (DataSource) bean.getObject();

To take advantage of the DI container you can also make the DataSource a Spring bean :

@Bean(destroyMethod = "")
public DataSource jndiDataSource() throws IllegalArgumentException, NamingException {
    JndiObjectFactoryBean bean = new JndiObjectFactoryBean();
    return (DataSource) bean.getObject();

And so you can now inject the DataSource in any Spring beans such as :

private DataSource jndiDataSource;

Note that many examples on the internet seem to disable the lookup of the JNDI resource on startup :


But I think that it is helpless as it invokes just after afterPropertiesSet() that does the lookup !

An Authentication object was not found in the SecurityContext - Spring 3.2.2

For me, the problem was a ContextRefreshedEvent handler. I was doing some data initilization but at that point in the application the Authentication had not been set. It was a catch 22 since the system needed an authentication to authorize and it needed authorization to get the authentication details :). I ended up loosening the authorization from a class level to a method level.

Visual Studio debugging/loading very slow

Each time I recompiled to local host while developing it took several minutes. It was terribly frustrating. After trying umpteen fixes including putting it all on an SSD. I found what really worked. I created a ramdisk and put the whole project in it. Recompiles to local host are now under ten seconds. Perhaps not elegant but it really worked.

Requested bean is currently in creation: Is there an unresolvable circular reference?

I think you could use Spring's


annotation on one of the autowired fields to break circular dependency.

I'm not sure if this works/exists in mentioned Spring version.

How to use JNDI DataSource provided by Tomcat in Spring?

Documentation: C.2.3.1 <jee:jndi-lookup/> (simple)


<jee:jndi-lookup id="dataSource" jndi-name="jdbc/MyDataSource"/>

You just need to find out what JNDI name your appserver has bound the datasource to. This is entirely server-specific, consult the docs on your server to find out how.

Remember to declare the jee namespace at the top of your beans file, as described in C.2.3 The jee schema.

What does java:comp/env/ do?

There is also a property resourceRef of JndiObjectFactoryBean that is, when set to true, used to automatically prepend the string java:comp/env/ if it is not already present.

<bean id="someId" class="org.springframework.jndi.JndiObjectFactoryBean">
  <property name="jndiName" value="jdbc/loc"/>
  <property name="resourceRef" value="true"/>

LINQ order by null column where order is ascending and nulls should be last

It really helps to understand the LINQ query syntax and how it is translated to LINQ method calls.

It turns out that

var products = from p in _context.Products
               where p.ProductTypeId == 1
               orderby p.LowestPrice.HasValue descending
               orderby p.LowestPrice descending
               select p;

will be translated by the compiler to

var products = _context.Products
                       .Where(p => p.ProductTypeId == 1)
                       .OrderByDescending(p => p.LowestPrice.HasValue)
                       .OrderByDescending(p => p.LowestPrice)
                       .Select(p => p);

This is emphatically not what you want. This sorts by Product.LowestPrice.HasValue in descending order and then re-sorts the entire collection by Product.LowestPrice in descending order.

What you want is

var products = _context.Products
                       .Where(p => p.ProductTypeId == 1)
                       .OrderByDescending(p => p.LowestPrice.HasValue)
                       .ThenBy(p => p.LowestPrice)
                       .Select(p => p);

which you can obtain using the query syntax by

var products = from p in _context.Products
               where p.ProductTypeId == 1
               orderby p.LowestPrice.HasValue descending,
               select p;

For details of the translations from query syntax to method calls, see the language specification. Seriously. Read it.

How to update a pull request from forked repo?

Just push to the branch that the pull request references. As long as the pull request is still open, it should get updated with any added commits automatically.

MySQL Event Scheduler on a specific time everyday



SET GLOBAL event_scheduler = ON;

In php, is 0 treated as empty?

use only ($_POST['input_field_name'])!=0 instead of !($_POST['input_field_name'])==0 then 0 is not treated as empty.

How to check what version of jQuery is loaded?

…just because this method hasn't been mentioned so far - open the console and type:

$ === jQuery

As @Juhana mentioned above $().jquery will return the version number.

Renaming Columns in an SQL SELECT Statement

you have to rename each column

SELECT col1 as MyCol1,
       col2 as MyCol2,
 FROM `foobar`

External VS2013 build error "error MSB4019: The imported project <path> was not found"

This is closely related but may or may not fix OPs specific issue. In my case I was trying to automate the deployment of an Azure site using VS2013. Building and deploying via VS works, however, using MSBuild showed a similar error around the "targets". Turns out MSBuild is different under VS2013, and is now part of VS and not the .Net Framework (see Basically, use the correct version of MSBuild:

OLD, VS2012


NEW, VS2013

C:\Program Files (x86)\MSBuild\12.0\bin\msbuild.exe

Newer, VS2015

C:\Program Files (x86)\MSBuild\14.0\Bin\msbuild.exe

Newer still, VS2017 (not fully testing but discovered - they've moved things around a bit)

C:\Program Files (x86)\Microsoft Visual Studio\2017\Professional\MSBuild\15.0\Bin\msbuild.exe

Java: Enum parameter in method

Sure, you could use an enum. Would something like the following work?

enum Alignment {

private static String drawCellValue(int maxCellLength, String cellValue, Alignment alignment) { }

If you wanted to use a boolean, you could rename the align parameter to something like alignLeft. I agree that this implementation is not as clean, but if you don't anticipate a lot of changes and this is not a public interface, it might be a good choice.

how to get session id of client in Client

Try from your code socket.socket.sessionid ie.

    var socket = io.connect('http://localhost');
  var sendBtn= document.getElementById('btnSend');
  sendBtn.onclick= function(){
var userId=document.getElementById('txt1').value;
var userMsg = document.getElementById('txt2').value;
socket.emit('sendto',{username: userId, message: userMsg});

  socket.on('news', function (data) {
    socket.emit('my other event', { my: 'data' });
  socket.on('message',function(data){ console.log(data);});

How to fix "unable to write 'random state' " in openssl

I did not find where the .rnd file is so I ran the cmd as administrator and it worked like a charm.

Filter dict to contain only certain keys?

Based on the accepted answer by delnan.

What if one of your wanted keys aren't in the old_dict? The delnan solution will throw a KeyError exception that you can catch. If that's not what you need maybe you want to:

  1. only include keys that excists both in the old_dict and your set of wanted_keys.

    old_dict = {'name':"Foobar", 'baz':42}
    wanted_keys = ['name', 'age']
    new_dict = {k: old_dict[k] for k in set(wanted_keys) & set(old_dict.keys())}
    >>> new_dict
    {'name': 'Foobar'}
  2. have a default value for keys that's not set in old_dict.

    default = None
    new_dict = {k: old_dict[k] if k in old_dict else default for k in wanted_keys}
    >>> new_dict
    {'age': None, 'name': 'Foobar'}

How can I make a div not larger than its contents?

The solution is to set your div to display: inline-block.

Declare an empty two-dimensional array in Javascript?

var arr = [];_x000D_
var rows = 3;_x000D_
var columns = 2;_x000D_
for (var i = 0; i < rows; i++) {_x000D_
    arr.push([]); // creates arrays in arr_x000D_
console.log('elements of arr are arrays:');_x000D_
for (var i = 0; i < rows; i++) {_x000D_
    for (var j = 0; j < columns; j++) {_x000D_
        arr[i][j] = null; // empty 2D array: it doesn't make much sense to do this_x000D_
console.log('empty 2D array:');_x000D_
for (var i = 0; i < rows; i++) {_x000D_
    for (var j = 0; j < columns; j++) {_x000D_
        arr[i][j] = columns * i + j + 1;_x000D_
console.log('2D array filled with values:');_x000D_

Return JsonResult from web api without its properties

When using WebAPI, you should just return the Object rather than specifically returning Json, as the API will either return JSON or XML depending on the request.

I am not sure why your WebAPI is returning an ActionResult, but I would change the code to something like;

public IEnumerable<ListItems> GetAllNotificationSettings()
    var result = new List<ListItems>();
    // Filling the list with data here...

    // Then I return the list
    return result;

This will result in JSON if you are calling it from some AJAX code.

P.S WebAPI is supposed to be RESTful, so your Controller should be called ListItemController and your Method should just be called Get. But that is for another day.

XSL xsl:template match="/"

It's worth noting, since it's confusing for people new to XML, that the root (or document node) of an XML document is not the top-level element. It's the parent of the top-level element. This is confusing because it doesn't seem like the top-level element can have a parent. Isn't it the top level?

But look at this, a well-formed XML document:

<?xml-stylesheet href="my_transform.xsl" type="text/xsl"?>
<!-- Comments and processing instructions are XML nodes too, remember. -->

The root of this document has three children: a processing instruction, a comment, and an element.

So, for example, if you wanted to write a transform that got rid of that comment, but left in any comments appearing anywhere else in the document, you'd add this to the identity transform:

<xsl:template match="/comment()"/>

Even simpler (and more commonly useful), here's an XPath pattern that matches the document's top-level element irrespective of its name: /*.

click command in selenium webdriver does not work

There's nothing wrong with either version of your code. Whatever is causing this, that's not it.

Have you triple checked your locator? Your element definitely has name=submit not id=submit?

What is "Signal 15 received"

This indicates the linux has delivered a SIGTERM to your process. This is usually at the request of some other process (via kill()) but could also be sent by your process to itself (using raise()). This signal requests an orderly shutdown of your process.

If you need a quick cheatsheet of signal numbers, open a bash shell and:

$ kill -l
63) SIGRTMAX-1  64) SIGRTMAX    

You can determine the sender by using an appropriate signal handler like:

#include <signal.h>
#include <stdio.h>
#include <stdlib.h>

void sigterm_handler(int signal, siginfo_t *info, void *_unused)
  fprintf(stderr, "Received SIGTERM from process with pid = %u\n",

int main (void)
  struct sigaction action = {
    .sa_handler = NULL,
    .sa_sigaction = sigterm_handler,
    .sa_mask = 0,
    .sa_flags = SA_SIGINFO,
    .sa_restorer = NULL

  sigaction(SIGTERM, &action, NULL);

  return 0;

Notice that the signal handler also includes a call to exit(). It's also possible for your program to continue to execute by ignoring the signal, but this isn't recommended in general (if it's a user doing it there's a good chance it will be followed by a SIGKILL if your process doesn't exit, and you lost your opportunity to do any cleanup then).

numpy: most efficient frequency counts for unique values in an array

Take a look at np.bincount:

import numpy as np
x = np.array([1,1,1,2,2,2,5,25,1,1])
y = np.bincount(x)
ii = np.nonzero(y)[0]

And then:

# [(1, 5), (2, 3), (5, 1), (25, 1)]


# array([[ 1,  5],
         [ 2,  3],
         [ 5,  1],
         [25,  1]])

or however you want to combine the counts and the unique values.

How to download and save an image in Android

I have just came from solving this problem on and I would like to share the complete code that can download, save to the sdcard (and hide the filename) and retrieve the images and finally it checks if the image is already there. The url comes from the database so the filename can be uniquely easily using id.

first download images

   private class GetImages extends AsyncTask<Object, Object, Object> {
    private String requestUrl, imagename_;
    private ImageView view;
    private Bitmap bitmap ; 
      private FileOutputStream fos;
    private GetImages(String requestUrl, ImageView view, String _imagename_) {
        this.requestUrl = requestUrl;
        this.view = view;
        this.imagename_ = _imagename_ ;

    protected Object doInBackground(Object... objects) {
        try {
            URL url = new URL(requestUrl);
            URLConnection conn = url.openConnection();
            bitmap = BitmapFactory.decodeStream(conn.getInputStream());
        } catch (Exception ex) {
        return null;

    protected void onPostExecute(Object o) { 
                ImageStorage.saveToSdCard(bitmap, imagename_); 

Then create a class for saving and retrieving the files

  public class ImageStorage {

public static String saveToSdCard(Bitmap bitmap, String filename) {

    String stored = null;

    File sdcard = Environment.getExternalStorageDirectory() ; 

    File folder = new File(sdcard.getAbsoluteFile(), ".your_specific_directory");//the dot makes this directory hidden to the user
    File file = new File(folder.getAbsoluteFile(), filename + ".jpg") ;
    if (file.exists())
        return stored ;

    try {
        FileOutputStream out = new FileOutputStream(file);
        bitmap.compress(Bitmap.CompressFormat.JPEG, 90, out);
        stored = "success";
    } catch (Exception e) {
     return stored;

public static File getImage(String imagename) {

        File mediaImage = null;
        try {
            String root = Environment.getExternalStorageDirectory().toString();
            File myDir = new File(root);
            if (!myDir.exists())
                return null;

            mediaImage = new File(myDir.getPath() + "/.your_specific_directory/"+imagename);
        } catch (Exception e) {
            // TODO Auto-generated catch block
        return mediaImage;
public static boolean checkifImageExists(String imagename)
    Bitmap b = null ;
    File file = ImageStorage.getImage("/"+imagename+".jpg");
    String path = file.getAbsolutePath();

    if (path != null)
        b = BitmapFactory.decodeFile(path); 

    if(b == null ||  b.equals(""))
        return false ;
    return true ;

Then To access the images first check if it is already there if not then download

                File file = ImageStorage.getImage("/"+imagename+".jpg"); 
                String path = file.getAbsolutePath(); 
                if (path != null){
                    b = BitmapFactory.decodeFile(path);
            } else { 
                new GetImages(imgurl, imageView, imagename).execute() ; 

If table exists drop table then create it, if it does not exist just create it

Just put DROP TABLE IF EXISTS `tablename`; before your CREATE TABLE statement.

That statement drops the table if it exists but will not throw an error if it does not.

How to bind Events on Ajax loaded Content?

Important step for Event binding on Ajax loading content...

01. First of all unbind or off the event on selector


02. Add event listener on document level

$(document).on("EVENT", '.SELECTOR', function(event) { 
    console.log("Selector event occurred");

Python pandas: fill a dataframe row by row

df['y'] will set a column

since you want to set a row, use .loc

Note that .ix is equivalent here, yours failed because you tried to assign a dictionary to each element of the row y probably not what you want; converting to a Series tells pandas that you want to align the input (for example you then don't have to to specify all of the elements)

In [7]: df = pandas.DataFrame(columns=['a','b','c','d'], index=['x','y','z'])

In [8]: df.loc['y'] = pandas.Series({'a':1, 'b':5, 'c':2, 'd':3})

In [9]: df
     a    b    c    d
x  NaN  NaN  NaN  NaN
y    1    5    2    3
z  NaN  NaN  NaN  NaN

How to correctly link php-fpm and Nginx Docker containers?

I think we also need to give the fpm container the volume, dont we? So =>

    image: php:fpm
        - ./:/var/www/test/

If i dont do this, i run into this exception when firing a request, as fpm cannot find requested file:

[error] 6#6: *4 FastCGI sent in stderr: "Primary script unknown" while reading response header from upstream, client:, server: localhost, request: "GET / HTTP/1.1", upstream: "fastcgi://", host: "localhost"

Get list of filenames in folder with Javascript

The current code will give a list of all files in a folder, assuming it's on the server side you want to list all files:

var fs = require('fs');
var files = fs.readdirSync('/assets/photos/');

Rails Active Record find(:all, :order => ) issue

isn't it only :order => 'column1 ASC, column2 DESC'?

Get startup type of Windows service using PowerShell

WMI is the way to do this.

Get-WmiObject -Query "Select StartMode From Win32_Service Where Name='winmgmt'"


Get-WmiObject -Class Win32_Service -Property StartMode -Filter "Name='Winmgmt'"

How to transform currentTimeMillis to a readable date format?

There is a simpler way in Android


Moreover, Date is deprecated, so use DateFormat class.

   DateFormat.getDateInstance().format(new Date(0));  
   DateFormat.getDateTimeInstance().format(new Date(0));  
   DateFormat.getTimeInstance().format(new Date(0));  

The above three lines will give:

Dec 31, 1969  
Dec 31, 1969 4:00:00 PM  
4:00:00 PM  12:00:00 AM

Android Dialog: Removing title bar

create your XML which is shown in dialog here it is activity_no_title_dialog

final Dialog dialog1 = new Dialog(context);

Error 415 Unsupported Media Type: POST not reaching REST if JSON, but it does if XML

I encountered the same issue in postman, i was selecting Accept in header section and providing the value as "application/json". So i unchecked and selected Content-Type and provided the value as "application/json". That worked!

What is the best way to convert an array to a hash in Ruby


Ruby 2.1.0 is released today. And I comes with Array#to_h (release notes and ruby-doc), which solves the issue of converting an Array to a Hash.

Ruby docs example:

[[:foo, :bar], [1, 2]].to_h    # => {:foo => :bar, 1 => 2}

Python math module

You can also import as

from math import *

Then you can use any mathematical function without prefixing math. e.g.


Get values from other sheet using VBA


did not work. However the following code only worked for me.

SomeVal = ThisWorkbook.Sheets(2).cells(aRow,aCol).Value

datetime datatype in java

java.util.Date represents an instant in time, with no reference to a particular time zone or calendar system. It does hold both date and time though - it's basically a number of milliseconds since the Unix epoch.

Alternatively you can use java.util.Calendar which does know about both of those things.

Personally I would strongly recommend you use Joda Time which is a much richer date/time API. It allows you to express your data much more clearly, with types for "just dates", "just local times", "local date/time", "instant", "date/time with time zone" etc. Most of the types are also immutable, which is a huge benefit in terms of code clarity.

Email and phone Number Validation in android

He want an elegant and proper solution try this small regex pattern matcher.

This is specifically for India.(First digit can't be zero and and then can be any 9 digits) return mobile.matches("[1-9][0-9]{9}");

Pattern Breakdown:-

[1-9] matches first digit and checks if number(integer) lies between(inclusive) 1 to 9 [0-9]{9} matches the same thing but {9} tells the pattern that it has to check for upcoming all 9 digits.

Now the {9} part may vary for different countries so you may have array which tells the number of digits allowed in phone number. Some countries also have significance for zero ahead of number, so you may have exception for those and design a separate regex patterns for those countries phone numbers.

Twig ternary operator, Shorthand if-then-else

You can use shorthand syntax as of Twig 1.12.0

{{ foo ?: 'no' }} is the same as {{ foo ? foo : 'no' }}
{{ foo ? 'yes' }} is the same as {{ foo ? 'yes' : '' }}

Showing the stack trace from a running Python application

You can use the hypno package, like so:

hypno <pid> "import traceback; traceback.print_stack()"

This would print a stack trace into the program's stdout.

Alternatively, if you don't want to print anything to stdout, or you don't have access to it (a daemon for example), you could use the madbg package, which is a python debugger that allows you to attach to a running python program and debug it in your current terminal. It is similar to pyrasite and pyringe, but newer, doesn't require gdb, and uses IPython for the debugger (which means colors and autocomplete).

To see the stack trace of a running program, you could run:

madbg attach <pid>

And in the debugger shell, enter: bt

Disclaimer - I wrote both packages

How do I remove blank pages coming between two chapters in Appendix?

You can also use \openany, \openright and \openleft commands:



This is the appendix.


How do I kill the process currently using a port on localhost in Windows?

Result for Windows Command Prompt

In my case, 8080 is the port I want to kill
And 18264 is the PID listening on port 8080
So the task you have to kill is the PID for that particular port

C:\Users\Niroshan>netstat -ano|findstr "PID :8080"

Proto Local Address Foreign Address State PID

taskkill /PID 18264 /f

Loop through an array in JavaScript

var x = [4, 5, 6];
for (i = 0, j = x[i]; i < x.length; j = x[++i]) {

A lot cleaner...

Oracle select most recent date record

i think i'd try with MAX something like this:

SELECT staff_id, max( date ) from owner.table group by staff_id

then link in your other columns:

select staff_id, site_id, pay_level, latest
from owner.table, 
(   SELECT staff_id, max( date ) latest from owner.table group by staff_id ) m
where m.staff_id = staff_id
and m.latest = date

Java: How to convert List to Map

Many solutions come to mind, depending on what you want to achive:

Every List item is key and value

for( Object o : list ) {

List elements have something to look them up, maybe a name:

for( MyObject o : list ) {

List elements have something to look them up, and there is no guarantee that they are unique: Use Googles MultiMaps

for( MyObject o : list ) {

Giving all the elements the position as a key:

for( int i=0; i<list.size; i++ ) {


It really depends on what you want to achive.

As you can see from the examples, a Map is a mapping from a key to a value, while a list is just a series of elements having a position each. So they are simply not automatically convertible.

How to get the first item from an associative PHP array?

Just so that we have some other options: reset($arr); good enough if you're not trying to keep the array pointer in place, and with very large arrays it incurs an minimal amount of overhead. That said, there are some problems with it:

$arr = array(1,2);
current($arr); // 1
next($arr);    // 2
current($arr); // 2
reset($arr);   // 1
current($arr); // 1 !This was 2 before! We've changed the array's pointer.

The way to do this without changing the pointer:

$arr[reset(array_keys($arr))]; // OR

The benefit of $arr[reset(array_keys($arr))]; is that it raises an warning if the array is actually empty.

Changing color of Twitter bootstrap Nav-Pills

Step 1: Define a class named applycolor which can be used to apply the color you choose.

Step 2: Define what actions happens to it when it hovers. If your form background is white, then you must make sure that on hover the tab does not turn white. To achieve this use the !important clause to force this feature on hover property. We are doing this to override Bootstrap's default behavior.

Step 3: Apply the class to the Tabs which you are targetting.

CSS section:

    .nav-pills > > a, .nav-pills > > a:hover, .nav-pills > > a:focus {
        color: #fff;
        background-color: #337ab7 !important;

    .nav > li > a:hover, .nav > li > a:focus {
        text-decoration: none;
        background-color: none !important;

    .applycolor {
        background-color: #efefef;
        text-decoration: none;
        color: #fff;

    .applycolor:hover {
        background-color: #337ab7;
        text-decoration: none;
        color: #fff;

Tab Section :

<section class="form-toolbar row">
    <div class="form-title col-sm-12" id="tabs">
        <ul class="nav nav-pills nav-justified">
            <li class="applycolor"><a data-toggle="pill" href="#instance" style="font-size: 1.8rem; font-weight: 800;">My Apps</a></li>
            <li class="active applycolor"><a data-toggle="pill" href="#application" style="font-size: 1.8rem; font-weight: 800;">Apps Collection</a></li>

How can I divide two integers to get a double?

var result = decimal.ToDouble(decimal.Divide(5, 2));

Apply function to each column in a data frame observing each columns existing data type

The reason that max works with apply is that apply is coercing your data frame to a matrix first, and a matrix can only hold one data type. So you end up with a matrix of characters. sapply is just a wrapper for lapply, so it is not surprising that both yield the same error.

The default behavior when you create a data frame is for categorical columns to be stored as factors. Unless you specify that it is an ordered factor, operations like max and min will be undefined, since R is assuming that you've created an unordered factor.

You can change this behavior by specifying options(stringsAsFactors = FALSE), which will change the default for the entire session, or you can pass stringsAsFactors = FALSE in the data.frame() construction call itself. Note that this just means that min and max will assume "alphabetical" ordering by default.

Or you can manually specify an ordering for each factor, although I doubt that's what you want to do.

Regardless, sapply will generally yield an atomic vector, which will entail converting everything to characters in many cases. One way around this is as follows:

#Some test data
d <- data.frame(v1 = runif(10), v2 = letters[1:10], 
                v3 = rnorm(10), v4 = LETTERS[1:10],stringsAsFactors = TRUE)

d[4,] <- NA

#Similar function to DWin's answer          
fun <- function(x){
    if(is.numeric(x)){max(x,na.rm = 1)}

#Use colwise from plyr package
         v1 v2       v3 v4
1 0.8478983  j 1.999435  J

When using .net MVC RadioButtonFor(), how do you group so only one selection can be made?

In my case, I had a collection of radio buttons that needed to be in a group. I just included a 'Selected' property in the model. Then, in the loop to output the radiobuttons just do...

@Html.RadioButtonFor(m => Model.Selected, Model.Categories[i].Title)

This way, the name is the same for all radio buttons. When the form is posted, the 'Selected' property is equal to the category title (or id or whatever) and this can be used to update the binding on the relevant radiobutton, like this...

model.Categories.Find(m => m.Title.Equals(model.Selected)).Selected = true;

May not be the best way, but it does work.

How to detect if a browser is Chrome using jQuery?

var is_chrome = /chrome/.test( navigator.userAgent.toLowerCase() );

How to set response header in JAX-RS so that user sees download popup for Excel?

You don't need HttpServletResponse to set a header on the response. You can do it using Just make your method to return Response instead of entity:

return Response.ok(entity).header("Content-Disposition", "attachment; filename=\"" + fileName + "\"").build()

If you still want to use HttpServletResponse you can get it either injected to one of the class fields, or using property, or to method parameter:

class MyResource {

  // one way to get HttpServletResponse
  private HttpServletResponse anotherServletResponse;

  // another way
  Response myMethod(@Context HttpServletResponse servletResponse) {
      // ... code

Center a popup window on screen?

I had an issue with centering a popup window in the external monitor and window.screenX and window.screenY were negative values (-1920, -1200) respectively. I have tried all the above of the suggested solutions and they worked well in primary monitors. I wanted to leave

  • 200 px margin for left and right
  • 150 px margin for top and bottom

Here is what worked for me:

 function createPopupWindow(url) {
    var height = screen.height;
    var width = screen.width;
    var left, top, win;

    if (width > 1050) {
        width = width - 200;
    } else {
        width = 850;

    if (height > 850) {
        height = height - 150;
    } else {
        height = 700;

    if (window.screenX < 0) {
        left = (window.screenX - width) / 2;
    } else {
        left = (screen.width - width) / 2;

    if (window.screenY < 0) {
        top = (window.screenY + height) / 4;
    } else {
        top = (screen.height - height) / 4;
    } url,"myTarget", "width="+width+", height="+height+",left="+left+",top="+top+"menubar=no, status=no, location=no, resizable=yes, scrollbars=yes");
    if (win.focus) {

How to find files recursively by file type and copy them to a directory while in ssh?

Something like this should work.

ssh [email protected] 'find -type f -name "*.pdf" -exec cp {} ./pdfsfolder \;'

How to check if a variable is an integer in JavaScript?

For positive integer values without separators:

return ( data !== '' && data === data.replace(/\D/, '') );

Tests 1. if not empty and 2. if value is equal to the result of a replace of a non-digit char in its value.

How do I navigate to a parent route from a child route?

This seems to work for me as of Spring 2017:

goBack(): void {
  this.router.navigate(['../'], { relativeTo: this.route });

Where your component ctor accepts ActivatedRoute and Router, imported as follows:

import { ActivatedRoute, Router } from '@angular/router';

How to use <md-icon> in Angular Material?

All md- prefixes are now mat- prefixes as of time of writing this!

Put this in your html head:

<link href="" rel="stylesheet">

Import in our module:

import { MatIconModule } from '@angular/material';

Use in your code:


Here is the latest documentation:

How to host material icons offline?

With angular cli

npm install angular-material-icons --save


npm install material-design-icons-iconfont --save

material-design-icons-iconfont is the latest updated version of the icons. angular-material-icons is not updated for a long time

Wait wait wait install to be done and then add it to angular.json -> projects -> architect -> styles

 "styles": [

or if you installed material-desing-icons-iconfont then

"styles": [

How to use terminal commands with Github?

git add myfile.h
git commit -m "your commit message"
git push -u origin master

if you don't remember all the files you need to update, use

git status

Using jquery to delete all elements with a given id

id of dom element shout be unique. Use class instead (<span class='myclass'>). To remove all span with this class:


Creating layout constraints programmatically

Hi I have been using this page a lot for constraints and "how to". It took me forever to get to the point of realizing I needed:

myView.translatesAutoresizingMaskIntoConstraints = NO;

to get this example to work. Thank you Userxxx, Rob M. and especially larsacus for the explanation and code here, it has been invaluable.

Here is the code in full to get the examples above to run:

UIView *myView = [[UIView alloc] init];
myView.backgroundColor = [UIColor redColor];
myView.translatesAutoresizingMaskIntoConstraints = NO;  //This part hung me up 
[self.view addSubview:myView];
//needed to make smaller for iPhone 4 dev here, so >=200 instead of 748
[self.view addConstraints:[NSLayoutConstraint

[self.view addConstraints:[NSLayoutConstraint

failed to open stream: HTTP wrapper does not support writeable connections

Instead of doing file_put_contents(***WebSiteURL***...) you need to use the server path to /cache/lang/file.php (e.g. /home/content/site/folders/filename.php).

You cannot open a file over HTTP and expect it to be written. Instead you need to open it using the local path.

Is there a way to link someone to a YouTube Video in HD 1080p quality?

No, this is not working. And it's not just for you, in case you spent the last hour trying to find an answer for having your embeded videos open in HD.

Question: Oh, but how do you know this is not working anymore and there is no other alternative to make embeded videos open in a different quality?

Answer: Just went to Google's official documentation regarding Youtube's player parameters and there is not a single parameter that allows you to change its quality.

Also, hd=1 doesn't work either. More info here.

Apparently Youtube analyses the width and height of the user's window (or iframe) and automatically sets the quality based on this.


As of 10 of April of 2018 it still doesn't work (see my comment on the accepted answer for more details).

What I can see from comments is that it MAY work sometimes, but some others it doesn't. The accepted answer states that "it measures the network speed and the screen and player sizes". So, by that, we can understand that I CANNOT force HD as YouTube will still do whatever it wants in case of low network speed/screen resolution. From my perspective everyone saying it works just have false positives on their hands and on the occasion they tested it worked for some random reason not related to the vq parameter. If it was a valid parameter, Google would document it somewhere, and vq isn't documented anywhere.

How do I know the script file name in a Bash script?

somthing like this?

export LC_ALL=en_US.UTF-8

ver=" v0.0.4"
$TRASH_DIR  # url to trash $MY_USER
$TRASH_SIZE # Show Trash Folder Size

echo "Would you like to empty Trash  [y/n]?"
read ans
if [ $ans = y -o $ans = Y -o $ans = yes -o $ans = Yes -o $ans = YES ]
echo "'yes'"
if [ $ans = n -o $ans = N -o $ans = no -o $ans = No -o $ans = NO ]
echo "'no'"
 return $TRUE

echo "HELP COMMANDS-----------------------------"
echo "htest www                 open a homepage "
echo "htest trash               empty trash     "
 return $TRUE
} #end Help


return $TRUE
} #end cpdebtemp

# -Case start
# if no command line arg given
# set val to Unknown
if [ -z $1 ]
  val="*** Unknown  ***"
elif [ -n $1 ]
# otherwise make first arg as val
# use case statement to make decision for rental
case $val in
   "trash") start_trash ;;
   "help") start_help ;;
   "www") firefox $homepage ;;
   *) echo "Sorry, I can not get a $val   for you!";;
# Case stop

Select Rows with id having even number

SELECT * FROM ( SELECT *, Row_Number() 
OVER(ORDER BY country_gid) AS sdfg  FROM eka_mst_tcountry ) t 
WHERE t.country_gid % 2 = 0 

Customize Bootstrap checkboxes

As others have said, the style you're after is actually just the Mac OS checkbox style, so it will look radically different on other devices.

In fact both screenshots you linked show what checkboxes look like on Mac OS in Chrome, the grey one is shown at non-100% zoom levels.

What's the difference between Apache's Mesos and Google's Kubernetes

Kubernetes and Mesos are a match made in heaven. Kubernetes enables the Pod (group of co-located containers) abstraction, along with Pod labels for service discovery, load-balancing, and replication control. Mesos provides the fine-grained resource allocations for pods across nodes in a cluster, and can make Kubernetes play nicely with other frameworks running on the same cluster resources.

from readme of kubernetes-mesos

Javascript - removing undefined fields from an object

Mhh.. I think @Damian asks for remove undefined field (property) from an JS object. Then, I would simply do :

for (const i in myObj)  
   if (typeof myObj[i] === 'undefined')   
     delete myObj[i]; 

Short and efficient solution, in (vanilla) JS ! Example :

const myObj = {_x000D_
  a: 1,_x000D_
  b: undefined,_x000D_
  c: null, _x000D_
  d: 'hello world'_x000D_
for (const i in myObj)  _x000D_
  if (typeof myObj[i] === 'undefined')   _x000D_
    delete myObj[i]; _x000D_

Constructor of an abstract class in C#

Because there might be a standard way you want to instantiate data in the abstract class. That way you can have classes that inherit from that class call the base constructor.

public abstract class A{

    private string data;

    protected A(string myString){
      data = myString;


public class B : A {

     B(string myString) : base(myString){}


Jquery to change form action

For variety's sake:

var actions = {input1: "action1.php", input2: "action2.php"};
$("#input1, #input2").click(function() {
    $(this).closest("form").attr("action", actions[]);

Referencing Row Number in R

These are present by default as rownames when you create a data.frame.

R> df = data.frame('a' = rnorm(10), 'b' = runif(10), 'c' = letters[1:10])
R> df
            a          b c
1   0.3336944 0.39746731 a
2  -0.2334404 0.12242856 b
3   1.4886706 0.07984085 c
4  -1.4853724 0.83163342 d
5   0.7291344 0.10981827 e
6   0.1786753 0.47401690 f
7  -0.9173701 0.73992239 g
8   0.7805941 0.91925413 h
9   0.2469860 0.87979229 i
10  1.2810961 0.53289335 j

and you can access them via the rownames command.

R> rownames(df)
 [1] "1"  "2"  "3"  "4"  "5"  "6"  "7"  "8"  "9"  "10"

if you need them as numbers, simply coerce to numeric by adding as.numeric, as in as.numeric(rownames(df)).

You don't need to add them, as if you know what you are looking for (say item df$c == 'i', you can use the which command:

R> which(df$c =='i')
[1] 9

or if you don't know the column

R> which(df == 'i', arr.ind=T)
     row col
[1,]   9   3

you may access the element using df[9, 'c'], or df$c[9].

If you wanted to add them you could use df$rownumber <- as.numeric(rownames(df)), though this may be less robust than df$rownumber <- 1:nrow(df) as there are cases when you might have assigned to rownames so they will no longer be the default index numbers (the which command will continue to return index numbers even if you do assign to rownames).

How to check if a service is running on Android?

You can use this (I didn't try this yet, but I hope this works):

if(startService(someIntent) != null) {
    Toast.makeText(getBaseContext(), "Service is already running", Toast.LENGTH_SHORT).show();
else {
    Toast.makeText(getBaseContext(), "There is no service running, starting service..", Toast.LENGTH_SHORT).show();

The startService method returns a ComponentName object if there is an already running service. If not, null will be returned.

See public abstract ComponentName startService (Intent service).

This is not like checking I think, because it's starting the service, so you can add stopService(someIntent); under the code.

Display a decimal in scientific notation

Here's an example using the format() function:

>>> "{:.2E}".format(Decimal('40800000000.00000000000000'))

Instead of format, you can also use f-strings:

>>> f"{Decimal('40800000000.00000000000000'):.2E}"

How do I pass a unique_ptr argument to a constructor or a function?

Base(Base::UPtr n):next(std::move(n)) {}

should be much better as

Base(Base::UPtr&& n):next(std::forward<Base::UPtr>(n)) {}


void setNext(Base::UPtr n)

should be

void setNext(Base::UPtr&& n)

with same body.

And ... what is evt in handle() ??

Write to UTF-8 file in Python

I believe the problem is that codecs.BOM_UTF8 is a byte string, not a Unicode string. I suspect the file handler is trying to guess what you really mean based on "I'm meant to be writing Unicode as UTF-8-encoded text, but you've given me a byte string!"

Try writing the Unicode string for the byte order mark (i.e. Unicode U+FEFF) directly, so that the file just encodes that as UTF-8:

import codecs

file ="lol", "w", "utf-8")

(That seems to give the right answer - a file with bytes EF BB BF.)

EDIT: S. Lott's suggestion of using "utf-8-sig" as the encoding is a better one than explicitly writing the BOM yourself, but I'll leave this answer here as it explains what was going wrong before.

Highcharts - how to have a chart with dynamic height?

I had the same problem and I fixed it with:

<div id="container" style="width: 100%; height: 100%; position:absolute"></div>

The chart fits perfect to the browser even if I resize it. You can change the percentage according to your needs.

How to make an AJAX call without jQuery?


You can use the XMLHttpRequest() constructor to create a new XMLHttpRequest (XHR) object which will allow you to interact with a server using standard HTTP request methods (such as GET and POST):

const data = JSON.stringify({
  example_1: 123,
  example_2: 'Hello, world!',

const request = new XMLHttpRequest();

request.addEventListener('load', function () {
  if (this.readyState === 4 && this.status === 200) {
});'POST', 'example.php', true);
request.setRequestHeader('Content-Type', 'application/x-www-form-urlencoded; charset=UTF-8');


You can also use the fetch() method to obtain a Promise which resolves to the Response object representing the response to your request:

const data = JSON.stringify({
  example_1: 123,
  example_2: 'Hello, world!',

fetch('example.php', {
  method: 'POST',
  headers: {
    'Content-Type': 'application/x-www-form-urlencoded; charset=UTF-8',
  body: data,
}).then(response => {
  if (response.ok) {
    response.text().then(response => {


On the other hand, if you are simply attempting to POST data and do not need a response from the server, the shortest solution would be to use navigator.sendBeacon():

const data = JSON.stringify({
  example_1: 123,
  example_2: 'Hello, world!',

navigator.sendBeacon('example.php', data);

Bootstrap Dropdown menu is not working

In case anyone still facing same problem be sure to check your your view Page source in your browser to check whether all the jquery and bootstrap files are loaded and paths to the file are correct. Most important! make sure to use latest stable jquery file.

How do I find out what all symbols are exported from a shared object?

see man nm

GNU nm lists the symbols from object files objfile.... If no object files are listed as arguments, nm assumes the file a.out.

How to expand and compute log(a + b)?

In general, one doesn't expand out log(a + b); you just deal with it as is. That said, there are occasionally circumstances where it makes sense to use the following identity:

log(a + b) = log(a * (1 + b/a)) = log a + log(1 + b/a)

(In fact, this identity is often used when implementing log in math libraries).

Split string in Lua?

A lot of these answers only accept single-character separators, or don't deal with edge cases well (e.g. empty separators), so I thought I would provide a more definitive solution.

Here are two functions, gsplit and split, adapted from the code in the Scribunto MediaWiki extension, which is used on wikis like Wikipedia. The code is licenced under the GPL v2. I have changed the variable names and added comments to make the code a bit easier to understand, and I have also changed the code to use regular Lua string patterns instead of Scribunto's patterns for Unicode strings. The original code has test cases here.

-- gsplit: iterate over substrings in a string separated by a pattern
-- Parameters:
-- text (string)    - the string to iterate over
-- pattern (string) - the separator pattern
-- plain (boolean)  - if true (or truthy), pattern is interpreted as a plain
--                    string, not a Lua pattern
-- Returns: iterator
-- Usage:
-- for substr in gsplit(text, pattern, plain) do
--   doSomething(substr)
-- end
local function gsplit(text, pattern, plain)
  local splitStart, length = 1, #text
  return function ()
    if splitStart then
      local sepStart, sepEnd = string.find(text, pattern, splitStart, plain)
      local ret
      if not sepStart then
        ret = string.sub(text, splitStart)
        splitStart = nil
      elseif sepEnd < sepStart then
        -- Empty separator!
        ret = string.sub(text, splitStart, sepStart)
        if sepStart < length then
          splitStart = sepStart + 1
          splitStart = nil
        ret = sepStart > splitStart and string.sub(text, splitStart, sepStart - 1) or ''
        splitStart = sepEnd + 1
      return ret

-- split: split a string into substrings separated by a pattern.
-- Parameters:
-- text (string)    - the string to iterate over
-- pattern (string) - the separator pattern
-- plain (boolean)  - if true (or truthy), pattern is interpreted as a plain
--                    string, not a Lua pattern
-- Returns: table (a sequence table containing the substrings)
local function split(text, pattern, plain)
  local ret = {}
  for match in gsplit(text, pattern, plain) do
    table.insert(ret, match)
  return ret

Some examples of the split function in use:

local function printSequence(t)

printSequence(split('foo, bar,baz', ',%s*'))       -- foo     bar     baz
printSequence(split('foo, bar,baz', ',%s*', true)) -- foo, bar,baz
printSequence(split('foo', ''))                    -- f       o       o

How does the "view" method work in PyTorch?

Let's try to understand view by the following examples:



    tensor([ 1.,  2.,  3.,  4.,  5.,  6.,  7.,  8.,  9., 10., 11., 12., 13., 14.,
            15., 16.])


    tensor([[ 1.,  2.],
            [ 3.,  4.],
            [ 5.,  6.],
            [ 7.,  8.],
            [ 9., 10.],
            [11., 12.],
            [13., 14.],
            [15., 16.]])

print(a.view(2,-1,4))   #3d tensor

    tensor([[[ 1.,  2.,  3.,  4.],
             [ 5.,  6.,  7.,  8.]],

            [[ 9., 10., 11., 12.],
             [13., 14., 15., 16.]]])

    tensor([[[ 1.,  2.],
             [ 3.,  4.],
             [ 5.,  6.],
             [ 7.,  8.]],

            [[ 9., 10.],
             [11., 12.],
             [13., 14.],
             [15., 16.]]])


    tensor([[[ 1.,  2.],
             [ 3.,  4.]],

            [[ 5.,  6.],
             [ 7.,  8.]],

            [[ 9., 10.],
             [11., 12.]],

            [[13., 14.],
             [15., 16.]]])

-1 as an argument value is an easy way to compute the value of say x provided we know values of y, z or the other way round in case of 3d and for 2d again an easy way to compute the value of say x provided we know values of y or vice versa..

size of NumPy array

This is called the "shape" in NumPy, and can be requested via the .shape attribute:

>>> a = zeros((2, 5))
>>> a.shape
(2, 5)

If you prefer a function, you could also use numpy.shape(a).

Use awk to find average of a column

Try this:

ls -l  | awk -F : '{sum+=$5} END {print "AVG=",sum/NR}'

NR is an AWK builtin variable to count the no. of records

Jquery show/hide table rows

The filter function wasn't working for me at all; maybe the more recent version of jquery doesn't perform as the version used in above code. Regardless; I used:

    var black = $('.black');
    var white = $('.white');

The selector will find every element classed under black or white. Button functions stay as stated above:

    $('#showBlackButton').click(function() {

    $('#showWhiteButton').click(function() {

MVC Razor @foreach

a reply to @DarinDimitrov for a case where i have used foreach in a razor view.

<li><label for="category">Category</label>
        <select id="category">
            <option value="0">All</option>
            @foreach(Category c in Model.Categories)
                <option title="@c.Description" value="@c.CategoryID">@c.Name</option>

Add border-bottom to table row <tr>

I had a problem like this before. I don't think tr can take a border styling directly. My workaround was to style the tds in the row:

<tr class="border_bottom">


tr.border_bottom td {
  border-bottom: 1px solid black;

How to install Android Studio on Ubuntu?

You could always follow the official guide on how to install Android Studio on Linux. There's even a video you can watch!

Remember to select Linux in the drop-down box.

Screenshot of video

To summarise the steps: download Android Studio and extract it and execute to run it. If you're running 64-bit Ubuntu, you will need to run:

sudo apt-get install lib32z1 lib32ncurses5 lib32bz2-1.0 lib32stdc++6

How to display list of repositories from subversion server

If you enable svn via apache and a SVNParentPath directive, you can add a SVNListParentPath On directive to your svn location to get a list of all repositories.

Your apache conf should look similar to this:

<Location /svn>
  DAV svn
  SVNParentPath         "/net/svn/repositories"
  # optional auth stuff     

  SVNListParentPath On    #  <--- Add this line to enable listing of all repos

TypeError: only length-1 arrays can be converted to Python scalars while trying to exponentially fit data

Here is another way to reproduce this error in Python2.7 with numpy:

import numpy as np
a = np.array([1,2,3])
b = np.array([4,5,6])
c = np.concatenate(a,b)   #note the lack of tuple format for a and b

The np.concatenate method produces an error:

TypeError: only length-1 arrays can be converted to Python scalars

If you read the documentation around numpy.concatenate, then you see it expects a tuple of numpy array objects. So surrounding the variables with parens fixed it:

import numpy as np
a = np.array([1,2,3])
b = np.array([4,5,6])
c = np.concatenate((a,b))  #surround a and b with parens, packaging them as a tuple

Then it prints:

[1 2 3 4 5 6]

What's going on here?

That error is a case of bubble-up implementation - it is caused by duck-typing philosophy of python. This is a cryptic low-level error python guts puke up when it receives some unexpected variable types, tries to run off and do something, gets part way through, the pukes, attempts remedial action, fails, then tells you that "you can't reformulate the subspace responders when the wind blows from the east on Tuesday".

In more sensible languages like C++ or Java, it would have told you: "you can't use a TypeA where TypeB was expected". But Python does it's best to soldier on, does something undefined, fails, and then hands you back an unhelpful error. The fact we have to be discussing this is one of the reasons I don't like Python, or its duck-typing philosophy.

Make div 100% Width of Browser Window

Try to give it a postion: absolute;

Is there a way to override class variables in Java?

Variables don't take part in overrinding. Only methods do. A method call is resolved at runtime, that is, the decision to call a method is taken at runtime, but the variables are decided at compile time only. Hence that variable is called whose reference is used for calling and not of the runtime object.

Take a look at following snippet:

package com.demo;

class Bike {
  int max_speed = 90;
  public void disp_speed() {
    System.out.println("Inside bike");

public class Honda_bikes extends Bike {
  int max_speed = 150;
  public void disp_speed() {
    System.out.println("Inside Honda");

public static void main(String[] args) {
    Honda_bikes obj1 = new Honda_bikes();
    Bike obj2 = new Honda_bikes();
    Bike obj3 = new Bike();


    System.out.println("Max_Speed = " + obj1.max_speed);
    System.out.println("Max_Speed = " + obj2.max_speed);
    System.out.println("Max_Speed = " + obj3.max_speed);


When you run the code, console will show:

Inside Honda
Inside Honda
Inside bike

Max_Speed = 150
Max_Speed = 90
Max_Speed = 90

link_to image tag. how to add class to a tag

You can also try this

<li><%= link_to "", application_welcome_path, class: "navbar-brand metas-logo"    %></li>

Where "metas-logo" is a css class with a background image

ImportError: No module named BeautifulSoup

Try this from bs4 import BeautifulSoup

This might be a problem with Beautiful Soup, version 4, and the beta days. I just read this from the homepage.

How to install Guest addition in Mac OS as guest and Windows machine as host

You can use SSH and SFTP as suggested here.

  1. In the Guest OS (Mac OS X), open System Preferences > Sharing, then activate Remote Login; note the ip address specified in the Remote Login instructions, e.g. ssh [email protected]
  2. In VirtualBox, open Devices > Network > Network Settings > Advanced > Port Forwarding and specify Host IP =, Host Port 2222, Guest IP, Guest Port 22
  3. On the Host OS, run the following command sftp -P 2222 [email protected]; if you prefer a graphical interface, you can use FileZilla

Replace user and with the appropriate values relevant to your configuration.

How to put space character into a string name in XML?

As already mentioned the correct way to have a space in an XML file is by using \u0020 which is the unicode character for a space.


<string name="spelatonertext3">-4,\u00205,\u0020-5,\u00206,\u0020-6</string>

Other suggestions have said to use &#160; or &#032; but there is two downsides to this. The first downside is that these are ASCII characters so you are relying on something like a TextView to parse them. The second downside is that &#160; can sometimes cause strange wrapping in TextViews.

Implements vs extends: When to use? What's the difference?

In the most simple terms extends is used to inherit from a class and implements is used to apply an interface in your class


public class Bicycle {
    //properties and methods
public class MountainBike extends Bicycle {
    //new properties and methods


public interface Relatable {
    //stuff you want to put
public class RectanglePlus implements Relatable {
    //your class code

if you still have confusion read this:

Email validation using jQuery

You can create your own function

function emailValidate(email){
    var check = "" + email;
        if('@')<check.split('@')[1].search(/\./)'@')) return true;
        else return false;
    else return false;

alert(emailValidate('[email protected]'));

Traversing text in Insert mode

I believe Home and End (and PageUp/PageDn) also work normally while in insert mode, but aside from that, I don't believe there are any other standard keys defined for text traversal.

Control cannot fall through from one case label

You can do more than just fall through in C#, but you must utilize the "dreaded" goto statement. For example:

switch (whatever)
  case 2:
    Result.Write( "Subscribe" );
  case 1:
    Result.Write( "Un" );
    goto case 2;

How to get the IP address of the server on which my C# application is running on?

Here is how i solved it. i know if you have several physical interfaces this might not select the exact eth you want.

private string FetchIP()
    //Get all IP registered
    List<string> IPList = new List<string>();
    IPHostEntry host;
    host = Dns.GetHostEntry(Dns.GetHostName());
    foreach (IPAddress ip in host.AddressList)
        if (ip.AddressFamily == AddressFamily.InterNetwork)

    //Find the first IP which is not only local
    foreach (string a in IPList)
        Ping p = new Ping();
        string[] b = a.Split('.');
        string ip2 = b[0] + "." + b[1] + "." + b[2] + ".1";
        PingReply t = p.Send(ip2);
        if (t.Status == IPStatus.Success && ip2 != a)
            return a;
    return null;

How to build a 'release' APK in Android Studio?

AndroidStudio is alpha version for now. So you have to edit gradle build script files by yourself. Add next lines to your build.gradle

android {

    signingConfigs {

        release {

            storeFile file('android.keystore')
            storePassword "pwd"
            keyAlias "alias"
            keyPassword "pwd"

    buildTypes {

       release {

           signingConfig signingConfigs.release

To actually run your application at emulator or device run gradle installDebug or gradle installRelease.

You can create helloworld project from AndroidStudio wizard to see what structure of gradle files is needed. Or export gradle files from working eclipse project. Also this series of articles are helpfull

How is the default max Java heap size determined?

A number of parameters affect generation size. The following diagram illustrates the difference between committed space and virtual space in the heap. At initialization of the virtual machine, the entire space for the heap is reserved. The size of the space reserved can be specified with the -Xmx option. If the value of the -Xms parameter is smaller than the value of the -Xmx parameter, not all of the space that is reserved is immediately committed to the virtual machine. The uncommitted space is labeled "virtual" in this figure. The different parts of the heap (permanent generation, tenured generation and young generation) can grow to the limit of the virtual space as needed.

enter image description here

By default, the virtual machine grows or shrinks the heap at each collection to try to keep the proportion of free space to live objects at each collection within a specific range. This target range is set as a percentage by the parameters -XX:MinHeapFreeRatio=<minimum> and -XX:MaxHeapFreeRatio=<maximum>, and the total size is bounded below by -Xms<min> and above by -Xmx<max>.

Parameter Default Value

MinHeapFreeRatio 40

MaxHeapFreeRatio 70

-Xms 3670k

-Xmx 64m

Default values of heap size parameters on 64-bit systems have been scaled up by approximately 30%. This increase is meant to compensate for the larger size of objects on a 64-bit system.

With these parameters, if the percent of free space in a generation falls below 40%, the generation will be expanded to maintain 40% free space, up to the maximum allowed size of the generation. Similarly, if the free space exceeds 70%, the generation will be contracted so that only 70% of the space is free, subject to the minimum size of the generation.

Large server applications often experience two problems with these defaults. One is slow startup, because the initial heap is small and must be resized over many major collections. A more pressing problem is that the default maximum heap size is unreasonably small for most server applications. The rules of thumb for server applications are:

  • Unless you have problems with pauses, try granting as much memory as possible to the virtual machine. The default size (64MB) is often too small.
  • Setting -Xms and -Xmx to the same value increases predictability by removing the most important sizing decision from the virtual machine. However, the virtual machine is then unable to compensate if you make a poor choice.
  • In general, increase the memory as you increase the number of processors, since allocation can be parallelized.

    There is the full article

Convert blob to base64

var audioURL = window.URL.createObjectURL(blob);
audio.src = audioURL;

var reader = new window.FileReader();
reader.onloadend = function () {
     base64data = reader.result;

Decimal precision and scale in EF Code First

Entity Framework Ver 6 (Alpha, rc1) has something called Custom Conventions. To set decimal precision:

protected override void OnModelCreating(DbModelBuilder modelBuilder)
    modelBuilder.Properties<decimal>().Configure(config => config.HasPrecision(18, 4));


Passing a variable from node.js to html

What you can utilize is some sort of templating engine like pug (formerly jade). To enable it you should do the following:

  1. npm install --save pug - to add it to the project and package.json file
  2. app.set('view engine', 'pug'); - register it as a view engine in express
  3. create a ./views folder and add a simple .pug file like so:
    title= title
    h1= message

note that the spacing is very important!

  1. create a route that returns the processed html:
app.get('/', function (req, res) {
  res.render('index', { title: 'Hey', message: 'Hello there!'});

This will render an index.html page with the variables passed in node.js changed to the values you have provided. This has been taken directly from the expressjs templating engine page:

For more info on pug you can also check:

How do I change the title of the "back" button on a Navigation Bar

This work better for me. Try :

 self.navigationController.navigationBar.topItem.backBarButtonItem = [[UIBarButtonItem alloc] 
initWithTitle:@"Back" style:UIBarButtonItemStylePlain target:nil action:nil];

How to work with complex numbers in C?

The notion of complex numbers was introduced in mathematics, from the need of calculating negative quadratic roots. Complex number concept was taken by a variety of engineering fields.

Today that complex numbers are widely used in advanced engineering domains such as physics, electronics, mechanics, astronomy, etc...

Real and imaginary part, of a negative square root example:

#include <stdio.h>   
#include <complex.h>

int main() 
    int negNum;

    printf("Calculate negative square roots:\n"
           "Enter negative number:");

    scanf("%d", &negNum);

    double complex negSqrt = csqrt(negNum);

    double pReal = creal(negSqrt);
    double pImag = cimag(negSqrt);

    printf("\nReal part %f, imaginary part %f"
           ", for negative square root.(%d)",
           pReal, pImag, negNum);

    return 0;

Joining pairs of elements of a list

Without building temporary lists:

>>> import itertools
>>> s = 'abcdefgh'
>>> si = iter(s)
>>> [''.join(each) for each in itertools.izip(si, si)]
['ab', 'cd', 'ef', 'gh']


>>> import itertools
>>> s = 'abcdefgh'
>>> si = iter(s)
>>> map(''.join, itertools.izip(si, si))
['ab', 'cd', 'ef', 'gh']

Installing SQL Server 2012 - Error: Prior Visual Studio 2010 instances requiring update

I had this issue too, after following this guide, it was simply 1 additional patch that was required to get past the

Rule "Prior Visual Studio 2010 instances requiring update." failed.

Was to locate this file, and patch my machine


Simply do a file search on the installation media for SQL Server 2012, in my case it was in \redist\VisualStudioShell (whereas in the guide it's listed as being in a different location).

Then hit 're-run'.

Failed State

Printing leading 0's in C

The correct solution is to store the ZIP Code in the database as a STRING. Despite the fact that it may look like a number, it isn't. It's a code, where each part has meaning.

A number is a thing you do arithmetic on. A ZIP Code is not that.

Xcode 4 - build output directory

This was so annoying. Open your project, click on Target, Open Build Phases tab. Check your Copy Bundle Resources for any red items.

Difference between Dictionary and Hashtable

There is one more important difference between a HashTable and Dictionary. If you use indexers to get a value out of a HashTable, the HashTable will successfully return null for a non-existent item, whereas the Dictionary will throw an error if you try accessing a item using a indexer which does not exist in the Dictionary

GridLayout and Row/Column Span Woe

Android Support V7 GridLayout library makes excess space distribution easy by accommodating the principle of weight. To make a column stretch, make sure the components inside it define a weight or a gravity. To prevent a column from stretching, ensure that one of the components in the column does not define a weight or a gravity. Remember to add dependency for this library. Add in build.gradle.

<?xml version="1.0" encoding="utf-8"?>
< xmlns:android=""

    app:layout_rowWeight="1" />

    app:layout_rowWeight="1" />

    app:layout_rowWeight="1" />



Why does Git treat this text file as a binary file?

If git check-attr --all -- src/my_file.txt indicates that your file is flagged as binary, and you haven't set it as binary in .gitattributes, check for it in /.git/info/attributes.

Using CSS td width absolute, position

This may not be what you want to hear, but display: table-cell does not respect width and will be collapsed based on the width of the entire table. You can get around this easily just by having a display: block element inside of the table cell itself whose width you specify, e.g

<td><div style="width: 300px;">wide</div></td>

This shouldn't make much of a difference if the <table> itself is position: fixed or absolute because the position of the cells are all static relative to the table.

EDIT: I can't take credit, but as the comments say you can just use min-width instead of width on the table cell instead.

Attaching click event to a JQuery object not yet added to the DOM


    hover: function() {
        console.log("yeahhhh!!! but this doesn't work for me :(");
    click: function() {
        console.log("yeahhhh!!! but this doesn't work for me :(");

jsfiddle example.

When using .on() and binding to a dynamic element, you need to refer to an element that already exists on the page (like body in the example). If you can use a more specific element that would improve performance.

Event handlers are bound only to the currently selected elements; they must exist on the page at the time your code makes the call to .on(). To ensure the elements are present and can be selected, perform event binding inside a document ready handler for elements that are in the HTML markup on the page. If new HTML is being injected into the page, select the elements and attach event handlers after the new HTML is placed into the page. Or, use delegated events to attach an event handler, as described next.


How can I trigger another job from a jenkins pipeline (jenkinsfile) with GitHub Org Plugin?

The command build in pipeline is there to trigger other jobs in jenkins.

Example on github

The job must exist in Jenkins and can be parametrized. As for the branch, I guess you can read it from git

Spring @Autowired and @Qualifier

The @Qualifier annotation is used to resolve the autowiring conflict, when there are multiple beans of same type.

The @Qualifier annotation can be used on any class annotated with @Component or on methods annotated with @Bean. This annotation can also be applied on constructor arguments or method parameters.


public interface Vehicle {
     public void start();
     public void stop();

There are two beans, Car and Bike implements Vehicle interface

public class Car implements Vehicle {

     public void start() {
           System.out.println("Car started");

     public void stop() {
           System.out.println("Car stopped");

public class Bike implements Vehicle {

     public void start() {
          System.out.println("Bike started");

     public void stop() {
          System.out.println("Bike stopped");

Injecting Bike bean in VehicleService using @Autowired with @Qualifier annotation. If you didn't use @Qualifier, it will throw NoUniqueBeanDefinitionException.

public class VehicleService {

    private Vehicle vehicle;

    public void service() {

Reference:- @Qualifier annotation example

Fastest way to write huge data in text file Java

For these bulky reads from DB you may want to tune your Statement's fetch size. It might save a lot of roundtrips to DB. with headers

As the best anwser have writed using XMLHttpResponse except, and I make the abstracts-anwser as a instance.

The main Js file is download.js Download-JS

 // var download_url = window.BASE_URL+ "/waf/p1/download_rules";
    var download_url = window.BASE_URL+ "/waf/p1/download_logs_by_dt";
    function download33() {
        var sender_data = {"start_time":"2018-10-9", "end_time":"2018-10-17"};
        var x=new XMLHttpRequest();"POST", download_url, true);
//        x.setRequestHeader("Access-Control-Allow-Origin", "*");
        x.setRequestHeader("Authorization", "JWT " + localStorage.token );
        x.responseType = 'blob';
        x.onload=function(e){download(x.response, "", "application/zip" ); }
        x.send( JSON.stringify(sender_data) ); // post-data

Difference between 3NF and BCNF in simple terms (must be able to explain to an 8-year old)

The subtle difference is that 3NF makes a distinction between key and non-key attributes (also called non-prime attributes) whereas BCNF does not.

This is best explained using Zaniolo's definition of 3NF, which is equivalent to Codd's:

A relation, R, is in 3NF iff for every nontrivial FD (X->A) satisfied by R at least ONE of the following conditions is true:

(a) X is a superkey for R, or

(b) A is a key attribute for R

BCNF requires (a) but doesn't treat (b) as a special case of its own. In other words BCNF requires that every nontrivial determinant is a superkey even its dependent attributes happen to be part of a key.

A relation, R, is in BCNF iff for every nontrivial FD (X->A) satisfied by R the following condition is true:

(a) X is a superkey for R

BCNF is therefore more strict.

The difference is so subtle that what many people informally describe as 3NF is actually BCNF. For example, you stated here that 3NF means "data depends on the key[s]... and nothing but the key[s]", but that is really an informal description of BCNF and not 3NF. 3NF could more accurately be described as "non-key data depends on the keys... and nothing but the keys".

You also stated:

the 3NF quote explicitly says "nothing but the key" meaning that all attributes depend solely on the primary key.

That's an oversimplification. 3NF and BCNF and all the Normal Forms are concerned with all candidate keys and/or superkeys, not just one "primary" key.

How to stop/shut down an elasticsearch node?

Considering you have 3 nodes.

Prepare your cluster

export ES_HOST=localhost:9200

# Disable shard allocation
curl -X PUT "$ES_HOST/_cluster/settings" -H 'Content-Type: application/json' -d'
  "persistent": {
    "cluster.routing.allocation.enable": "none"

# Stop non-essential indexing and perform a synced flush
curl -X POST "$ES_HOST/_flush/synced"

Stop elasticsearch service in each node

# check nodes
export ES_HOST=localhost:9200
curl -X GET "$ES_HOST/_cat/nodes"

# node 1
systemctl stop elasticsearch.service

# node 2
systemctl stop elasticsearch.service

# node 3
systemctl stop elasticsearch.service

Restarting cluster again

# start
systemctl start elasticsearch.service

# Reenable shard allocation once the node has joined the cluster
curl -X PUT "$ES_HOST/_cluster/settings" -H 'Content-Type: application/json' -d'
  "persistent": {
    "cluster.routing.allocation.enable": null

Tested on Elasticseach 6.5



Android View shadow

If you are in need of the shadows properly to be applied then you have to do the following.

Consider this view, defined with a background drawable:

    android:background="@drawable/myrect" />

The background drawable is defined as a rectangle with rounded corners:

<shape xmlns:android=""
    <solid android:color="#42000000" />
    <corners android:radius="5dp" />

This is the recomended way of appying shadows check this out

"Fatal error: Unable to find local grunt." when running "grunt" command

if you are a exists project, maybe should execute npm install.

guntjs getting started step 2.

How can I set the default timezone in node.js?

Here's an answer for those deploying a Node.js application to Amazon AWS Elastic Beanstalk. I haven't seen this documented anywhere else:

Under Configuration -> Software -> Environment Properties, simply set the key value pair TZ and your time zone e.g. America/Los Angeles, and Apply the change.

You can verify the effect by outputting new Date().toString() in your Node app and paying attention to the time zone suffix.

jQuery multiple events to trigger the same function

It's simple to implement this with the built-in DOM methods without a big library like jQuery, if you want, it just takes a bit more code - iterate over an array of event names, and add a listener for each:

function validate() {
  // ...

const element = document.querySelector('#element');
['keyup', 'keypress', 'blur', 'change'].forEach((eventName) => {
  element.addEventListener(eventName, validate);

jQuery each loop in table row

In jQuery just use:

$('#tblOne > tbody  > tr').each(function() {...code...});

Using the children selector (>) you will walk over all the children (and not all descendents), example with three rows:

$('table > tbody  > tr').each(function(index, tr) { 



In VanillaJS you can use document.querySelectorAll() and walk over the rows using forEach()

[]'#tblOne > tbody  > tr'), function(index, tr) {
    /* console.log(index); */
    /* console.log(tr); */

How to remove border from specific PrimeFaces p:panelGrid?

If you just want something more simple, you can just change:

<p:panelGrid >



<h:panelGrid border="0">


That's worked fine for me

Android sample bluetooth code to send a simple string via bluetooth

I made the following code so that even beginners can understand. Just copy the code and read comments. Note that message to be send is declared as a global variable which you can change just before sending the message. General changes can be done in Handler function.

import android.annotation.SuppressLint;
import android.bluetooth.BluetoothAdapter;
import android.bluetooth.BluetoothDevice;
import android.bluetooth.BluetoothServerSocket;
import android.bluetooth.BluetoothSocket;
import android.content.Intent;
import android.os.Bundle;
import android.os.Handler;
import android.os.Message;
import android.view.View;
import android.widget.AdapterView;
import android.widget.ArrayAdapter;
import android.widget.ListView;
import android.widget.Toast;

import java.util.ArrayList;
import java.util.Set;
import java.util.UUID;

public class multiplayerConnect extends AppCompatActivity {

public static final int REQUEST_ENABLE_BT=1;
ListView lv_paired_devices;
Set<BluetoothDevice> set_pairedDevices;
ArrayAdapter adapter_paired_devices;
BluetoothAdapter bluetoothAdapter;
public static final UUID MY_UUID = UUID.fromString("00001101-0000-1000-8000-00805F9B34FB");
public static final int MESSAGE_READ=0;
public static final int MESSAGE_WRITE=1;
public static final int CONNECTING=2;
public static final int CONNECTED=3;
public static final int NO_SOCKET_FOUND=4;

String bluetooth_message="00";

Handler mHandler=new Handler()
    public void handleMessage(Message msg_type) {

        switch (msg_type.what){
            case MESSAGE_READ:

                byte[] readbuf=(byte[])msg_type.obj;
                String string_recieved=new String(readbuf);

                //do some task based on recieved string

            case MESSAGE_WRITE:

                    ConnectedThread connectedThread=new ConnectedThread((BluetoothSocket)msg_type.obj);


            case CONNECTED:

            case CONNECTING:

            case NO_SOCKET_FOUND:
                Toast.makeText(getApplicationContext(),"No socket found",Toast.LENGTH_SHORT).show();

protected void onCreate(@Nullable Bundle savedInstanceState) {


public void start_accepting_connection()
    //call this on button click as suited by you

    AcceptThread acceptThread = new AcceptThread();
public void initialize_clicks()
    lv_paired_devices.setOnItemClickListener(new AdapterView.OnItemClickListener() {
        public void onItemClick(AdapterView<?> parent, View view, int position, long id)
            Object[] objects = set_pairedDevices.toArray();
            BluetoothDevice device = (BluetoothDevice) objects[position];

            ConnectThread connectThread = new ConnectThread(device);

            Toast.makeText(getApplicationContext(),"device choosen "+device.getName(),Toast.LENGTH_SHORT).show();

public void initialize_layout()
    lv_paired_devices = (ListView)findViewById(;
    adapter_paired_devices = new ArrayAdapter(getApplicationContext(),R.layout.support_simple_spinner_dropdown_item);

public void initialize_bluetooth()
    bluetoothAdapter = BluetoothAdapter.getDefaultAdapter();
    if (bluetoothAdapter == null) {
        // Device doesn't support Bluetooth
        Toast.makeText(getApplicationContext(),"Your Device doesn't support bluetooth. you can play as Single player",Toast.LENGTH_SHORT).show();

    //Add these permisions before
//        <uses-permission android:name="android.permission.BLUETOOTH" />
//        <uses-permission android:name="android.permission.BLUETOOTH_ADMIN" />
//        <uses-permission android:name="android.permission.ACCESS_COARSE_LOCATION" />
//        <uses-permission android:name="android.permission.ACCESS_FINE_LOCATION"/>

    if (!bluetoothAdapter.isEnabled()) {
        Intent enableBtIntent = new Intent(BluetoothAdapter.ACTION_REQUEST_ENABLE);
        startActivityForResult(enableBtIntent, REQUEST_ENABLE_BT);

    else {
        set_pairedDevices = bluetoothAdapter.getBondedDevices();

        if (set_pairedDevices.size() > 0) {

            for (BluetoothDevice device : set_pairedDevices) {
                String deviceName = device.getName();
                String deviceHardwareAddress = device.getAddress(); // MAC address

                adapter_paired_devices.add(device.getName() + "\n" + device.getAddress());

public class AcceptThread extends Thread
    private final BluetoothServerSocket serverSocket;

    public AcceptThread() {
        BluetoothServerSocket tmp = null;
        try {
            // MY_UUID is the app's UUID string, also used by the client code
            tmp = bluetoothAdapter.listenUsingRfcommWithServiceRecord("NAME",MY_UUID);
        } catch (IOException e) { }
        serverSocket = tmp;

    public void run() {
        BluetoothSocket socket = null;
        // Keep listening until exception occurs or a socket is returned
        while (true) {
            try {
                socket = serverSocket.accept();
            } catch (IOException e) {

            // If a connection was accepted
            if (socket != null)
                // Do work to manage the connection (in a separate thread)

private class ConnectThread extends Thread {
    private final BluetoothSocket mmSocket;
    private final BluetoothDevice mmDevice;

    public ConnectThread(BluetoothDevice device) {
        // Use a temporary object that is later assigned to mmSocket,
        // because mmSocket is final
        BluetoothSocket tmp = null;
        mmDevice = device;

        // Get a BluetoothSocket to connect with the given BluetoothDevice
        try {
            // MY_UUID is the app's UUID string, also used by the server code
            tmp = device.createRfcommSocketToServiceRecord(MY_UUID);
        } catch (IOException e) { }
        mmSocket = tmp;

    public void run() {
        // Cancel discovery because it will slow down the connection

        try {
            // Connect the device through the socket. This will block
            // until it succeeds or throws an exception

        } catch (IOException connectException) {
            // Unable to connect; close the socket and get out
            try {
            } catch (IOException closeException) { }

        // Do work to manage the connection (in a separate thread)
//            bluetooth_message = "Initial message"
//            mHandler.obtainMessage(MESSAGE_WRITE,mmSocket).sendToTarget();

    /** Will cancel an in-progress connection, and close the socket */
    public void cancel() {
        try {
        } catch (IOException e) { }
private class ConnectedThread extends Thread {

    private final BluetoothSocket mmSocket;
    private final InputStream mmInStream;
    private final OutputStream mmOutStream;

    public ConnectedThread(BluetoothSocket socket) {
        mmSocket = socket;
        InputStream tmpIn = null;
        OutputStream tmpOut = null;

        // Get the input and output streams, using temp objects because
        // member streams are final
        try {
            tmpIn = socket.getInputStream();
            tmpOut = socket.getOutputStream();
        } catch (IOException e) { }

        mmInStream = tmpIn;
        mmOutStream = tmpOut;

    public void run() {
        byte[] buffer = new byte[2];  // buffer store for the stream
        int bytes; // bytes returned from read()

        // Keep listening to the InputStream until an exception occurs
        while (true) {
            try {
                // Read from the InputStream
                bytes =;
                // Send the obtained bytes to the UI activity
                mHandler.obtainMessage(MESSAGE_READ, bytes, -1, buffer).sendToTarget();

            } catch (IOException e) {

    /* Call this from the main activity to send data to the remote device */
    public void write(byte[] bytes) {
        try {
        } catch (IOException e) { }

    /* Call this from the main activity to shutdown the connection */
    public void cancel() {
        try {
        } catch (IOException e) { }


<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android=""

        android:text="Challenge player"/>


        android:text="Make sure Device is paired"/>


At least one JAR was scanned for TLDs yet contained no TLDs

If one wants to have the conf\ read one must (see also here) dump this file into the Servers\Tomcat v7.0 Server at localhost-config\ folder and then add the lines :

-Djava.util.logging.config.file="${workspace_loc}\Servers\Tomcat v7.0 Server at localhost-config\" -Djava.util.logging.manager=org.apache.juli.ClassLoaderLogManager

to the VM arguments of the launch configuration one is using.

This may have taken a restart or two (or not) but finally I saw in the console in bright red :

FINE: No TLD files were found in [file:/C:/Dropbox/eclipse_workspaces/javaEE/.metadata/.plugins/org.eclipse.wst.server.core/tmp0/wtpwebapps/ted2012/WEB-INF/lib/logback-classic-1.0.7.jar]. Consider adding the JAR to the tomcat.util.scan.DefaultJarScanner.jarsToSkip or org.apache.catalina.startup.TldConfig.jarsToSkip property in CATALINA_BASE/conf/ file. //etc

I still don't know when exactly this FINE warning appears - does not appear immediately on tomcat launch EDIT: from the comment by @Stephan: "The FINE warning appears each time any change is done in the JSP file".

Bonus: To make the warning go away add in :

# Additional JARs (over and above the default JARs listed above) to skip when
# scanning for TLDs. The list must be a comma separated list of JAR file names.

How can I get useful error messages in PHP?

I have also seen such errors when the fastcgi_params or fastcgi.conf config file is not properly included in the server configuration. So the fix for me was a silly:

include /etc/nginx/fastcgi_params;

Took me an hour to find that out...

Changing nav-bar color after scrolling?

First you make an id named nav (can change whatever you want) inside the nav div (exp: id="nav") Then at the bottom where body tag had been finished. You add this code

   var scroll = $(window).scrollTop();
      $("#nav").css("background", "#555");
       else {
      $("#nav").css("background", "transparent");

Only mkdir if it does not exist

if [ ! -d directory ]; then
  mkdir directory


mkdir -p directory

-p ensures creation if directory does not exist

Is there a Social Security Number reserved for testing/examples?

There are multiple number groups and some particular numbers that will never be allocated:

Consider using one of these (the obviously invalid 000-00-0000 would be a good one IMO).

(Answer has been updated to provide source information beyond Wikipedia and remove information that is no longer accurate after the SSA made its randomization change in mid 2011.)

Document Root PHP

The Easiest way to do it is to have good site structure and write it as a constant.


How do I enumerate the properties of a JavaScript object?

for (prop in obj) {
    alert(prop + ' = ' + obj[prop]);

Including an anchor tag in an ASP.NET MVC Html.ActionLink

I don't remember in which version of ASP.NET MVC (ASP.NET MVC 3+ I believe) / Razor the parameterlabeldeclaration or whatever it's called (parameter: x) feature was introduced, but to me this is definitely the proper way to build a link with an anchor in ASP.NET MVC.

@Html.ActionLink("Some link text", "MyAction", "MyController", protocol: null, hostName: null, fragment: "MyAnchor", routeValues: null, htmlAttributes: null)

Not even Ed Blackburns antipattern argument from this answer can compete with that.

Error message: (provider: Shared Memory Provider, error: 0 - No process is on the other end of the pipe.)

I was getting this error today. In my case, looking at the ERRORLOG file on the SQL server gave me this error:

Login failed for user ''. Reason: Failed to open the database '' specified in the login properties.

This was because I had deleted the "Default database" of this user a few days ago. Setting the default database to my new database fixed the problem.

Hope this helps someone else.

How to SSH into Docker?

I guess it is possible. You just need to install a SSH server in each container and expose a port on the host. The main annoyance would be maintaining/remembering the mapping of port to container.

However, I have to question why you'd want to do this. SSH'ng into containers should be rare enough that it's not a hassle to ssh to the host then use docker exec to get into the container.

How to get a random number between a float range?

Use random.uniform(a, b):

>>> random.uniform(1.5, 1.9)

Send a ping to each IP on a subnet

In Bash shell:



while [ $COUNTER -lt 254 ]
   ping 192.168.1.$COUNTER -c 1
   COUNTER=$(( $COUNTER + 1 ))

How to declare a type as nullable in TypeScript?

You can just implement a user-defined type like the following:

type Nullable<T> = T | undefined | null;

var foo: Nullable<number> = 10; // ok
var bar: Nullable<number> = true; // type 'true' is not assignable to type 'Nullable<number>'
var baz: Nullable<number> = null; // ok

var arr1: Nullable<Array<number>> = [1,2]; // ok
var obj: Nullable<Object> = {}; // ok

 // Type 'number[]' is not assignable to type 'string[]'. 
 // Type 'number' is not assignable to type 'string'
var arr2: Nullable<Array<string>> = [1,2];

Display a jpg image on a JPanel

I'd probably use an ImageIcon and set it on a JLabel which I'd add to the JPanel.

Here's Sun's docs on the subject matter.

CSS ''background-color" attribute not working on checkbox inside <div>

Improving another answer here

input[type=checkbox] {
  cursor: pointer;
  margin-right: 10px;

input[type=checkbox]:after {
  content: " ";
  background-color: lightgray;
  display: inline-block;
  position: relative;
  top: -4px;
  width: 24px;
  height: 24px;
  margin-right: 10px;

input[type=checkbox]:checked:after {
  content: "\00a0\2714";

How to show/hide if variable is null

To clarify, the above example does work, my code in the example did not work for unrelated reasons.

If myvar is false, null or has never been used before (i.e. $scope.myvar or $rootScope.myvar never called), the div will not show. Once any value has been assigned to it, the div will show, except if the value is specifically false.

The following will cause the div to show:

$scope.myvar = "Hello World";


$scope.myvar = true;

The following will hide the div:

$scope.myvar = null;


$scope.myvar = false;

SQLite equivalent to ISNULL(), NVL(), IFNULL() or COALESCE()

Try this



select ifnull(InfoDetail,'') InfoDetail; -- this will replace null with ''
select ifnull(NULL,'THIS IS NULL');-- More clearly....

The ifnull() function returns a copy of its first non-NULL argument, or NULL if both arguments are NULL. Ifnull() must have exactly 2 arguments. The ifnull() function is equivalent to coalesce() with two arguments.

How do I set up Visual Studio Code to compile C++ code?

First of all, goto extensions (Ctrl + Shift + X) and install 2 extensions:

  1. Code Runner
  2. C/C++

Then, then reload the VS Code and select a play button on the top of the right corner your program runs in the output terminal. You can see output by Ctrl + Alt + N. To change other features goto user setting. enter image description here

When should you use constexpr capability in C++11?

There used to be a pattern with metaprogramming:

template<unsigned T>
struct Fact {
    enum Enum {
        VALUE = Fact<T-1>*T;

struct Fact<1u> {
    enum Enum {
        VALUE = 1;

// Fact<10>::VALUE is known be a compile-time constant

I believe constexpr was introduced to let you write such constructs without the need for templates and weird constructs with specialization, SFINAE and stuff - but exactly like you'd write a run-time function, but with the guarantee that the result will be determined in compile-time.

However, note that:

int fact(unsigned n) {
    if (n==1) return 1;
    return fact(n-1)*n;

int main() {
    return fact(10);

Compile this with g++ -O3 and you'll see that fact(10) is indeed evaulated at compile-time!

An VLA-aware compiler (so a C compiler in C99 mode or C++ compiler with C99 extensions) may even allow you to do:

int main() {
    int tab[fact(10)];
    int tab2[std::max(20,30)];

But that it's non-standard C++ at the moment - constexpr looks like a way to combat this (even without VLA, in the above case). And there's still the problem of the need to have "formal" constant expressions as template arguments.

How remove border around image in css?

Thank for the answers,

The border is removed for Internet Explorer, but this there for Firefox.

So, I added this class to the img:


And it worked!

How do I list one filename per output line in Linux?

you can use ls -1

ls -l will also do the work

Add values to app.config and retrieve them

This works:

public static void AddValue(string key, string value)
    Configuration config = ConfigurationManager.OpenExeConfiguration(Application.ExecutablePath);
    config.AppSettings.Settings.Add(key, value);

Delete a dictionary item if the key exists

Approach: calculate keys to remove, mutate dict

Let's call keys the list/iterator of keys that you are given to remove. I'd do this:

keys_to_remove = set(keys).intersection(set(mydict.keys()))
for key in keys_to_remove:
    del mydict[key]

You calculate up front all the affected items and operate on them.

Approach: calculate keys to keep, make new dict with those keys

I prefer to create a new dictionary over mutating an existing one, so I would probably also consider this:

keys_to_keep = set(mydict.keys()) - set(keys)
new_dict = {k: v for k, v in mydict.iteritems() if k in keys_to_keep}


keys_to_keep = set(mydict.keys()) - set(keys)
new_dict = {k: mydict[k] for k in keys_to_keep}

DB query builder toArray() laravel 4

You can do this using the query builder. Just use SELECT instead of TABLE and GET.

DB::select('select * from user where name = ?',['Jhon']);

Notes: 1. Multiple question marks are allowed. 2. The second parameter must be an array, even if there is only one parameter. 3. Laravel will automatically clean parameters, so you don't have to.

Further info here:

Hmmmmmm, turns out that still returns a standard class for me when I don't use a where clause. I found this helped:

foreach($results as $result)

However, get_object_vars isn't recursive, so don't use it on $results.

adding to window.onload event?

If you are using jQuery, you don't have to do anything special. Handlers added via $(document).ready() don't overwrite each other, but rather execute in turn:


If you are not using jQuery, you could use addEventListener, as demonstrated by Karaxuna, plus attachEvent for IE<9.

Note that onload is not equivalent to $(document).ready() - the former waits for CSS, images... as well, while the latter waits for the DOM tree only. Modern browsers (and IE since IE9) support the DOMContentLoaded event on the document, which corresponds to the jQuery ready event, but IE<9 does not.

  window.addEventListener('load', func1)
  window.attachEvent('onload', func1)
  window.addEventListener('load', func2)
  window.attachEvent('onload', func2)

If neither option is available (for example, you are not dealing with DOM nodes), you can still do this (I am using onload as an example, but other options are available for onload):

var oldOnload1=window.onload;
  oldOnload1 && oldOnload1();
var oldOnload2=window.onload;
  oldOnload2 && oldOnload2();

or, to avoid polluting the global namespace (and likely encountering namespace collisions), using the import/export IIFE pattern:

  return function(){
    oldLoad && oldLoad();
  return function(){
    oldLoad && oldLoad();

Java 8 LocalDate Jackson format

Simplest and shortest so far:

@JsonFormat(pattern = "yyyy-MM-dd")
private LocalDate localDate;

@JsonFormat(pattern = "yyyy-MM-dd HH:mm:ss")
private LocalDateTime localDateTime;

no dependency required with Spring boot >= 2.2+

How to specify preference of library path?

As an alternative, you can use the environment variables LIBRARY_PATH and CPLUS_INCLUDE_PATH, which respectively indicate where to look for libraries and where to look for headers (CPATH will also do the job), without specifying the -L and -I options.

Edit: CPATH includes header with -I and CPLUS_INCLUDE_PATH with -isystem.

How to include a Font Awesome icon in React's render()

The simplest solution is:


npm install --save @fortawesome/fontawesome-svg-core
npm install --save @fortawesome/free-solid-svg-icons
npm install --save @fortawesome/react-fontawesome


import { FontAwesomeIcon } from '@fortawesome/react-fontawesome';
import { faThumbsUp } from '@fortawesome/free-solid-svg-icons';


<FontAwesomeIcon icon={ faThumbsUp }/>

pandas groupby sort descending order

Similar to one of the answers above, but try adding .sort_values() to your .groupby() will allow you to change the sort order. If you need to sort on a single column, it would look like this:


ascending=False will sort from high to low, the default is to sort from low to high.

*Careful with some of these aggregations. For example .size() and .count() return different values since .size() counts NaNs.

What is the difference between size and count in pandas?

How to change the background color on a input checkbox with css?

I always use pseudo elements :before and :after for changing the appearance of checkboxes and radio buttons. it's works like a charm.

Refer this link for more info



  1. Hide the default checkbox using css rules like visibility:hidden or opacity:0 or position:absolute;left:-9999px etc.
  2. Create a fake checkbox using :before element and pass either an empty or a non-breaking space '\00a0';
  3. When the checkbox is in :checked state, pass the unicode content: "\2713", which is a checkmark;
  4. Add :focus style to make the checkbox accessible.
  5. Done

Here is how I did it.

.box {_x000D_
  background: #666666;_x000D_
  color: #ffffff;_x000D_
  width: 250px;_x000D_
  padding: 10px;_x000D_
  margin: 1em auto;_x000D_
p {_x000D_
  margin: 1.5em 0;_x000D_
  padding: 0;_x000D_
input[type="checkbox"] {_x000D_
  visibility: hidden;_x000D_
label {_x000D_
  cursor: pointer;_x000D_
input[type="checkbox"] + label:before {_x000D_
  border: 1px solid #333;_x000D_
  content: "\00a0";_x000D_
  display: inline-block;_x000D_
  font: 16px/1em sans-serif;_x000D_
  height: 16px;_x000D_
  margin: 0 .25em 0 0;_x000D_
  padding: 0;_x000D_
  vertical-align: top;_x000D_
  width: 16px;_x000D_
input[type="checkbox"]:checked + label:before {_x000D_
  background: #fff;_x000D_
  color: #333;_x000D_
  content: "\2713";_x000D_
  text-align: center;_x000D_
input[type="checkbox"]:checked + label:after {_x000D_
  font-weight: bold;_x000D_
input[type="checkbox"]:focus + label::before {_x000D_
    outline: rgb(59, 153, 252) auto 5px;_x000D_
<div class="content">_x000D_
  <div class="box">_x000D_
      <input type="checkbox" id="c1" name="cb">_x000D_
      <label for="c1">Option 01</label>_x000D_
      <input type="checkbox" id="c2" name="cb">_x000D_
      <label for="c2">Option 02</label>_x000D_
      <input type="checkbox" id="c3" name="cb">_x000D_
      <label for="c3">Option 03</label>_x000D_

Much more stylish using :before and :after

  font-family: sans-serif;  _x000D_
.container {_x000D_
    margin-top: 50px;_x000D_
    margin-left: 20px;_x000D_
    margin-right: 20px;_x000D_
.checkbox {_x000D_
    width: 100%;_x000D_
    margin: 15px auto;_x000D_
    position: relative;_x000D_
    display: block;_x000D_
.checkbox input[type="checkbox"] {_x000D_
    width: auto;_x000D_
    opacity: 0.00000001;_x000D_
    position: absolute;_x000D_
    left: 0;_x000D_
    margin-left: -20px;_x000D_
.checkbox label {_x000D_
    position: relative;_x000D_
.checkbox label:before {_x000D_
    content: '';_x000D_
    position: absolute;_x000D_
    left: 0;_x000D_
    top: 0;_x000D_
    margin: 4px;_x000D_
    width: 22px;_x000D_
    height: 22px;_x000D_
    transition: transform 0.28s ease;_x000D_
    border-radius: 3px;_x000D_
    border: 2px solid #7bbe72;_x000D_
.checkbox label:after {_x000D_
  content: '';_x000D_
    display: block;_x000D_
    width: 10px;_x000D_
    height: 5px;_x000D_
    border-bottom: 2px solid #7bbe72;_x000D_
    border-left: 2px solid #7bbe72;_x000D_
    -webkit-transform: rotate(-45deg) scale(0);_x000D_
    transform: rotate(-45deg) scale(0);_x000D_
    transition: transform ease 0.25s;_x000D_
    will-change: transform;_x000D_
    position: absolute;_x000D_
    top: 12px;_x000D_
    left: 10px;_x000D_
.checkbox input[type="checkbox"]:checked ~ label::before {_x000D_
    color: #7bbe72;_x000D_
.checkbox input[type="checkbox"]:checked ~ label::after {_x000D_
    -webkit-transform: rotate(-45deg) scale(1);_x000D_
    transform: rotate(-45deg) scale(1);_x000D_
.checkbox label {_x000D_
    min-height: 34px;_x000D_
    display: block;_x000D_
    padding-left: 40px;_x000D_
    margin-bottom: 0;_x000D_
    font-weight: normal;_x000D_
    cursor: pointer;_x000D_
    vertical-align: sub;_x000D_
.checkbox label span {_x000D_
    position: absolute;_x000D_
    top: 50%;_x000D_
    -webkit-transform: translateY(-50%);_x000D_
    transform: translateY(-50%);_x000D_
.checkbox input[type="checkbox"]:focus + label::before {_x000D_
    outline: 0;_x000D_
<div class="container"> _x000D_
  <div class="checkbox">_x000D_
     <input type="checkbox" id="checkbox" name="" value="">_x000D_
     <label for="checkbox"><span>Checkbox</span></label>_x000D_
  <div class="checkbox">_x000D_
     <input type="checkbox" id="checkbox2" name="" value="">_x000D_
     <label for="checkbox2"><span>Checkbox</span></label>_x000D_

Style the first <td> column of a table differently

If you've to support IE7, a more compatible solution is:

/* only the cells with no cell before (aka the first one) */
td {
    padding-left: 20px;
/* only the cells with at least one cell before (aka all except the first one) */
td + td {
    padding-left: 0;

Also works fine with li; general sibling selector ~ may be more suitable with mixed elements like a heading h1 followed by paragraphs AND a subheading and then again other paragraphs.

get size of json object

var json=[{"id":"431","code":"0.85.PSFR01215","price":"2457.77","volume":"23.0","total":"565.29"},{"id":"430","code":"0.85.PSFR00608","price":"1752.45","volume":"4.0","total":"70.1"},{"id":"429","code":"0.84.SMAB00060","price":"4147.5","volume":"2.0","total":"82.95"},{"id":"428","code":"0.84.SMAB00050","price":"4077.5","volume":"3.0","total":"122.32"}] 
var obj = JSON.parse(json);
var length = Object.keys(obj).length; //you get length json result 4


You could try


Now that won't do you any good if the code is running in the <head>, and running before the <body> has even been seen by the browser. If you don't want to mess with "onload" handlers, try moving your <script> block to the very end of the document instead of the <head>.

How to fill the whole canvas with specific color?

Yes, fill in a Rectangle with a solid color across the canvas, use the height and width of the canvas itself:

var canvas = document.getElementById("canvas");
var ctx = canvas.getContext("2d");
ctx.fillStyle = "blue";
ctx.fillRect(0, 0, canvas.width, canvas.height);
canvas{ border: 1px solid black; }
<canvas width=300 height=150 id="canvas">

How do I send a cross-domain POST request via JavaScript?

Keep it simple:

  1. cross-domain POST:
    use crossDomain: true,

  2. shouldn't refresh the page:
    No, it will not refresh the page as the success or error async callback will be called when the server send back the response.

Example script:

        type: "POST",
        url: "",
        crossDomain: true,
        data: 'param1=value1&param2=value2',
        success: function (data) {
            // do something with server response data
        error: function (err) {
            // handle your error logic here

How I can get web page's content and save it into the string variable

Webclient client = new Webclient();
string content = client.DownloadString(url);

Pass the URL of page who you want to get. You can parse the result using htmlagilitypack.

Angular 2 - NgFor using numbers instead collections

I solved it like this using Angular 5.2.6 and TypeScript 2.6.2:

class Range implements Iterable<number> {
        public readonly low: number,
        public readonly high: number,
        public readonly step: number = 1
    ) {

    *[Symbol.iterator]() {
        for (let x = this.low; x <= this.high; x += this.step) {
            yield x;

function range(low: number, high: number) {
    return new Range(low, high);

It can be used in a Component like this:

    template: `<div *ngFor="let i of r">{{ i }}</div>`
class RangeTestComponent {
    public r = range(10, 20);

Error checking and assertions omitted on purpose for brevity (e.g. what happens if step is negative).

Android, How to read QR code in my application?

try {

    Intent intent = new Intent("");
    intent.putExtra("SCAN_MODE", "QR_CODE_MODE"); // "PRODUCT_MODE for bar codes

    startActivityForResult(intent, 0);

} catch (Exception e) {

    Uri marketUri = Uri.parse("market://details?");
    Intent marketIntent = new Intent(Intent.ACTION_VIEW,marketUri);


and in onActivityResult():

protected void onActivityResult(int requestCode, int resultCode, Intent data) {           
    super.onActivityResult(requestCode, resultCode, data);
    if (requestCode == 0) {

        if (resultCode == RESULT_OK) {
            String contents = data.getStringExtra("SCAN_RESULT");
        if(resultCode == RESULT_CANCELED){
            //handle cancel

What does $1 mean in Perl?

I would suspect that there can be as many as 2**32 -1 numbered match variables, on a 32-bit compiled Perl binary.

Message 'src refspec master does not match any' when pushing commits in Git

None of the above solutions worked for me when I got the src-refspec error.

My workflow:

  • pushed to remote branch (same local branch name)
  • deleted that remote branch
  • changed some stuff & committed
  • pushed again to the same remote branch name (same local branch name)
  • got src-refspec error.

I fixed the error by simply making a new branch, and pushing again. (The weird thing was, I couldn't simply just rename the branch - it gave me fatal: Branch rename failed.)

GUI-based or Web-based JSON editor that works like property explorer

Generally when I want to create a JSON or YAML string, I start out by building the Perl data structure, and then running a simple conversion on it. You could put a UI in front of the Perl data structure generation, e.g. a web form.

Converting a structure to JSON is very straightforward:

use strict;
use warnings;
use JSON::Any;

my $data = { arbitrary structure in here };
my $json_handler = JSON::Any->new(utf8=>1);
my $json_string = $json_handler->objToJson($data);

Nginx serves .php files as downloads, instead of executing them

I had the same issue and none of the answers solved the problem.

I ran:

sudo nginx -t

to test the config file at /etc/nginx/sites-available/default.

It gave me these errors:

nginx: [emerg] unexpected end of file, expecting "}" in /etc/nginx/sites-enabled/default:115
nginx: configuration file /etc/nginx/nginx.conf test failed

So I went into the config file and on the last line there was


I uncommented, ran the test command again and it worked

Best practice for Django project working directory structure

My answer is inspired on my own working experience, and mostly in the book Two Scoops of Django which I highly recommend, and where you can find a more detailed explanation of everything. I just will answer some of the points, and any improvement or correction will be welcomed. But there also can be more correct manners to achieve the same purpose.

I have a main folder in my personal directory where I maintain all the projects where I am working on.

Source Files
I personally use the django project root as repository root of my projects. But in the book is recommended to separate both things. I think that this is a better approach, so I hope to start making the change progressively on my projects.


Git or Mercurial seem to be the most popular version control systems among Django developers. And the most popular hosting services for backups GitHub and Bitbucket.

Virtual Environment
I use virtualenv and virtualenvwrapper. After installing the second one, you need to set up your working directory. Mine is on my /home/envs directory, as it is recommended on virtualenvwrapper installation guide. But I don't think the most important thing is where is it placed. The most important thing when working with virtual environments is keeping requirements.txt file up to date.

pip freeze -l > requirements.txt 

Static Root
Project folder

Media Root
Project folder

Repository root

Repository root

Repository root. This python packages can help you making easier mantaining your documentation:




How to add rows dynamically into table layout

Solution 1. Set your TableLayout tl as class member variable, only call TableLayout tl=(TableLayout)findViewById(; when you initiate the class. When button clicked use tl directly, eg. tl.addView(row), don't call FindViewById anymore. So the next new row wouldn't replace the previous new row.

Solution 2. Everytime after button click save your updated data into an array, and then re-render your whole table layout by loop through the array.

Automated testing for REST Api

I have used TestNG and Apache HTTP classes to build my own REST API test framework, I developed this concept after working in Selenium for two years.

Everything is same, except you should use Apache HTTP classes instead of Selenium classes.

give a try, its really cute and good, you've all the power to customize your test framework to your fullest possibilities.

Manipulating an Access database from Java without ODBC

UCanAccess is a pure Java JDBC driver that allows us to read from and write to Access databases without using ODBC. It uses two other packages, Jackcess and HSQLDB, to perform these tasks. The following is a brief overview of how to get it set up.


Option 1: Using Maven

If your project uses Maven you can simply include UCanAccess via the following coordinates:

groupId: net.sf.ucanaccess
artifactId: ucanaccess

The following is an excerpt from pom.xml, you may need to update the <version> to get the most recent release:



Option 2: Manually adding the JARs to your project

As mentioned above, UCanAccess requires Jackcess and HSQLDB. Jackcess in turn has its own dependencies. So to use UCanAccess you will need to include the following components:

UCanAccess (ucanaccess-x.x.x.jar)
HSQLDB (hsqldb.jar, version 2.2.5 or newer)
Jackcess (jackcess-2.x.x.jar)
commons-lang (commons-lang-2.6.jar, or newer 2.x version)
commons-logging (commons-logging-1.1.1.jar, or newer 1.x version)

Fortunately, UCanAccess includes all of the required JAR files in its distribution file. When you unzip it you will see something like


All you need to do is add all five (5) JARs to your project.

NOTE: Do not add loader/ucanload.jar to your build path if you are adding the other five (5) JAR files. The UcanloadDriver class is only used in special circumstances and requires a different setup. See the related answer here for details.

Eclipse: Right-click the project in Package Explorer and choose Build Path > Configure Build Path.... Click the "Add External JARs..." button to add each of the five (5) JARs. When you are finished your Java Build Path should look something like this


NetBeans: Expand the tree view for your project, right-click the "Libraries" folder and choose "Add JAR/Folder...", then browse to the JAR file.


After adding all five (5) JAR files the "Libraries" folder should look something like this:


IntelliJ IDEA: Choose File > Project Structure... from the main menu. In the "Libraries" pane click the "Add" (+) button and add the five (5) JAR files. Once that is done the project should look something like this:



That's it!

Now "U Can Access" data in .accdb and .mdb files using code like this

// assumes...
//     import java.sql.*;
Connection conn=DriverManager.getConnection(
Statement s = conn.createStatement();
ResultSet rs = s.executeQuery("SELECT [LastName] FROM [Clients]");
while ( {



At the time of writing this Q&A I had no involvement in or affiliation with the UCanAccess project; I just used it. I have since become a contributor to the project.

Execution sequence of Group By, Having and Where clause in SQL Server?

I think it is implemented in the engine as Matthias said: WHERE, GROUP BY, HAVING

Was trying to find a reference online that lists the entire sequence (i.e. "SELECT" comes right down at the bottom), but I can't find it. It was detailed in a "Inside Microsoft SQL Server 2005" book I read not that long ago, by Solid Quality Learning

Edit: Found a link:

Get the Highlighted/Selected text

Get highlighted text this way:


and of course a special treatment for ie:


How to size an Android view based on its parent's dimensions

I've found that it's best not to mess around with setting the measured dimensions yourself. There's actually a bit of negotiation that goes on between the parent and child views and you don't want to re-write all that code.

What you can do, though, is modify the measureSpecs, then call super with them. Your view will never know that it's getting a modified message from its parent and will take care of everything for you:

protected void onMeasure(int widthMeasureSpec, int heightMeasureSpec) {
    int parentHeight = MeasureSpec.getSize(heightMeasureSpec);
    int myWidth = (int) (parentHeight * 0.5);
    super.onMeasure(MeasureSpec.makeMeasureSpec(myWidth, MeasureSpec.EXACTLY), heightMeasureSpec);

New to unit testing, how to write great tests?

Don't write tests to get full coverage of your code. Write tests that guarantee your requirements. You may discover codepaths that are unnecessary. Conversely, if they are necessary, they are there to fulfill some kind of requirement; find it what it is and test the requirement (not the path).

Keep your tests small: one test per requirement.

Later, when you need to make a change (or write new code), try writing one test first. Just one. Then you'll have taken the first step in test-driven development.

Any way to replace characters on Swift String?

Here is the example for Swift 3:

var stringToReplace = "This my string"
if let range = stringToReplace.range(of: "my") {
   stringToReplace?.replaceSubrange(range, with: "your")

100% width in React Native Flexbox

width: '100%' and alignSelf: 'stretch' didn't work for me. Dimensions didn't suite my task cause I needed to operate on a deeply nested view. Here's what worked for me, if I rewrite your code. I just added some more Views and used flex properties to achieve the needed layout:

  {/* a column */}
  <View style={styles.container}>
    {/* some rows here */}
    <Text style={styles.welcome}>
      Welcome to React Natives
    {/* this row should take all available width */}
    <View style={{ flexDirection: 'row' }}>
      {/* flex 1 makes the view take all available width */}
      <View style={{ flex: 1 }}>
        <Text style={styles.line1}>
      {/* I also had a button here, to the right of the text */}
    {/* the rest of the rows */}
    <Text style={styles.instructions}>
      Press Cmd+R to reload,{'\n'}
      Cmd+D or shake for dev menu

How to convert an array to a string in PHP?

serialize() and unserialize() convert between php objects and a string representation.

Create a button programmatically and set a background image

Update to Swift 3

let image = UIImage(named: "name")
let button = UIButton(type: .custom)
button.frame = CGRect(x: 100, y: 100, width: 100, height: 100)
button.setImage(image, for: .normal)
button.addTarget(self, action: #selector(self.btnAbsRetClicked(_:)), for:.touchUpInside)

What is the difference between 'SAME' and 'VALID' padding in tf.nn.max_pool of tensorflow?

Padding is an operation to increase the size of the input data. In case of 1-dimensional data you just append/prepend the array with a constant, in 2-dim you surround matrix with these constants. In n-dim you surround your n-dim hypercube with the constant. In most of the cases this constant is zero and it is called zero-padding.

Here is an example of zero-padding with p=1 applied to 2-d tensor: enter image description here

You can use arbitrary padding for your kernel but some of the padding values are used more frequently than others they are:

  • VALID padding. The easiest case, means no padding at all. Just leave your data the same it was.
  • SAME padding sometimes called HALF padding. It is called SAME because for a convolution with a stride=1, (or for pooling) it should produce output of the same size as the input. It is called HALF because for a kernel of size k enter image description here
  • FULL padding is the maximum padding which does not result in a convolution over just padded elements. For a kernel of size k, this padding is equal to k - 1.

To use arbitrary padding in TF, you can use tf.pad()

Java - Change int to ascii

The most simple way is using type casting:

public char toChar(int c) {
    return (char)c;

Isn't the size of character in Java 2 bytes?

There are some great answers here but I wanted to point out the jvm is free to store a char value in any size space >= 2 bytes.

On many architectures there is a penalty for performing unaligned memory access so a char might easily be padded to 4 bytes. A volatile char might even be padded to the size of the CPU cache line to prevent false sharing.

It might be non-intuitive to new Java programmers that a character array or a string is NOT simply multiple characters. You should learn and think about strings and arrays distinctly from "multiple characters".

I also want to point out that java characters are often misused. People don't realize they are writing code that won't properly handle codepoints over 16 bits in length.

Extract digits from string - StringUtils Java

A very simple solution, if separated by comma or if not separated by comma

public static void main(String[] args) {

    String input = "a,1,b,2,c,3,d,4";
    input = input.replaceAll(",", "");

    String alpha ="";
    String num = "";

    char[] c_arr = input.toCharArray();

    for(char c: c_arr) {
        if(Character.isDigit(c)) {
            alpha = alpha + c;
        else {
            num = num+c;

    System.out.println("Alphabet: "+ alpha);
    System.out.println("num: "+ num);


Twitter Bootstrap onclick event on buttons-radio

I see a lot of complicated answers, while this is super simple in Bootstrap 3:

Step 1: Use the official example code to create your radio button group, and give the container an id:

<div id="myButtons" class="btn-group" data-toggle="buttons">
  <label class="btn btn-primary active">
    <input type="radio" name="options" id="option1" autocomplete="off" checked> Radio 1 (preselected)
  <label class="btn btn-primary">
    <input type="radio" name="options" id="option2" autocomplete="off"> Radio 2
  <label class="btn btn-primary">
    <input type="radio" name="options" id="option3" autocomplete="off"> Radio 3

Step 2: Use this jQuery handler:

$("#myButtons :input").change(function() {
    console.log(this); // points to the clicked input button

Try the fiddle demo

MySQL create stored procedure syntax with delimiter

Getting started with stored procedure syntax in MySQL (using the terminal):

1. Open a terminal and login to mysql like this:

el@apollo:~$ mysql -u root -p
Enter password: 
Welcome to the MySQL monitor.  Commands end with ; or \g.

2. Take a look to see if you have any procedures:

mysql> show procedure status;
| Db        | Name          | Type      | Definer | Modified            | Created             | Security_type | Comment | character_set_client | collation_connection | Database Collation |
|   yourdb  | sp_user_login | PROCEDURE | root@%  | 2013-12-06 14:10:25 | 2013-12-06 14:10:25 | DEFINER       |         | utf8                 | utf8_general_ci      | latin1_swedish_ci  |
1 row in set (0.01 sec)

I have one defined, you probably have none to start out.

3. Change to the database, delete it.

mysql> use yourdb;
Database changed

mysql> drop procedure if exists sp_user_login;
Query OK, 0 rows affected (0.01 sec)
mysql> show procedure status;
Empty set (0.00 sec)

4. Ok so now I have no stored procedures defined. Make the simplest one:

mysql> delimiter //
mysql> create procedure foobar()
    -> begin select 'hello'; end//
Query OK, 0 rows affected (0.00 sec)

The // will communicate to the terminal when you are done entering commands for the stored procedure. the stored procedure name is foobar. it takes no parameters and should return "hello".

5. See if it's there, remember to set back your delimiter!:

 mysql> show procedure status;

Gotcha! Why didn't this work? You set the delimiter to // remember? Set it back to ;

6. Set the delimiter back and look at the procedure:

mysql> delimiter ;
mysql> show procedure status;
| Db        | Name   | Type      | Definer        | Modified            | Created             | Security_type | Comment | character_set_client | collation_connection | Database Collation |
| yourdb    | foobar | PROCEDURE | root@localhost | 2013-12-06 14:27:23 | 2013-12-06 14:27:23 | DEFINER       |         | utf8                 | utf8_general_ci      | latin1_swedish_ci  |
1 row in set (0.00 sec)


7. Run it:

mysql> call foobar();
| hello |
| hello |
1 row in set (0.00 sec)
Query OK, 0 rows affected (0.00 sec)

Hello world complete, lets overwrite it with something better.

8. Drop foobar, redefine it to accept a parameter, and re run it:

mysql> drop procedure foobar;
Query OK, 0 rows affected (0.00 sec)

mysql> show procedure status;
Empty set (0.00 sec)

mysql> delimiter //
mysql> create procedure foobar (in var1 int)
    -> begin select var1 + 2 as result;
    -> end//
Query OK, 0 rows affected (0.00 sec)

mysql> delimiter ;
mysql> call foobar(5);
| result |
|      7 |
1 row in set (0.00 sec)
Query OK, 0 rows affected (0.00 sec)

Nice! We made a procedure that takes input, modifies it, and does output. Now lets do an out variable.

9. Remove foobar, Make an out variable, run it:

mysql> delimiter ;
mysql> drop procedure foobar;
Query OK, 0 rows affected (0.00 sec)

mysql> delimiter //
mysql> create procedure foobar(out var1 varchar(100))
    -> begin set var1="kowalski, what's the status of the nuclear reactor?";
    -> end//
Query OK, 0 rows affected (0.00 sec)

mysql> delimiter ;
mysql> call foobar(@kowalski_status);
Query OK, 0 rows affected (0.00 sec)

mysql> select @kowalski_status;
| @kowalski_status                                    |
| kowalski, what's the status of the nuclear reactor? |
1 row in set (0.00 sec)

10. Example of INOUT usage in MySQL:

mysql> select 'ricksays' into @msg;
Query OK, 1 row affected (0.00 sec)

mysql> delimiter //
mysql> create procedure foobar (inout msg varchar(100))
-> begin
-> set msg = concat(@msg, " never gonna let you down");
-> end//

mysql> delimiter ;

mysql> call foobar(@msg);
Query OK, 0 rows affected (0.00 sec)

mysql> select @msg;
| @msg                              |
| ricksays never gonna let you down |
1 row in set (0.00 sec)

Ok it worked, it joined the strings together. So you defined a variable msg, passed in that variable into stored procedure called foobar, and @msg was written to by foobar.

Now you know how to make stored procedures with delimiters. Continue this tutorial here, start in on variables within stored procedures:

Convert row names into first column

Moved my comment into an answer per suggestion above:

You don't need extra packages, here's a one-liner:

d <- cbind(rownames(d), data.frame(d, row.names=NULL))

How do I import global modules in Node? I get "Error: Cannot find module <module>"?

I am using Docker. I am trying to create a docker image that has all of my node dependencies installed, but can use my local app directory at container run time (without polluting it with a node_modules directory or link). This causes problems in this scenario. My workaround is to require from the exact path where the module, e.g. require('/usr/local/lib/node_modules/')

Rebuild all indexes in a Database

Try the following script:



I prefer(After a long search) to use the following script, it contains @fillfactor determines how much percentage of the space on each leaf-level page is filled with data.

DECLARE @fillfactor INT
SET @fillfactor = 80 
FROM sys.tables
OPEN TableCursor
FETCH NEXT FROM TableCursor INTO @TableName
SET @sql = 'ALTER INDEX ALL ON ' + @TableName + ' REBUILD WITH (FILLFACTOR = ' + CONVERT(VARCHAR(3),@fillfactor) + ')'
EXEC (@sql)
FETCH NEXT FROM TableCursor INTO @TableName
CLOSE TableCursor

for more info, check the following link:

and if you want to Check Index Fragmentation on Indexes in a Database, try the following script:

SELECT dbschemas.[name] as 'Schema',
dbtables.[name] as 'Table',
dbindexes.[name] as 'Index',
FROM sys.dm_db_index_physical_stats (DB_ID(), NULL, NULL, NULL, NULL) AS indexstats
INNER JOIN sys.tables dbtables on dbtables.[object_id] = indexstats.[object_id]
INNER JOIN sys.schemas dbschemas on dbtables.[schema_id] = dbschemas.[schema_id]
INNER JOIN sys.indexes AS dbindexes ON dbindexes.[object_id] = indexstats.[object_id]
AND indexstats.index_id = dbindexes.index_id
WHERE indexstats.database_id = DB_ID() AND dbtables.[name] like '%%'
ORDER BY indexstats.avg_fragmentation_in_percent desc

For more information, Check the following link:

How to remove a row from JTable?

A JTable normally forms the View part of an MVC implementation. You'll want to remove rows from your model. The JTable, which should be listening for these changes, will update to reflect this removal. Hence you won't find removeRow() or similar as a method on JTable.

Setting a Sheet and cell as variable

Yes. For that ensure that you declare the worksheet

For example

Previous Code

Sub Sample()
    Dim ws As Worksheet

    Set ws = Sheets("Sheet3")

    Debug.Print ws.Cells(23, 4).Value
End Sub

New Code

Sub Sample()
    Dim ws As Worksheet

    Set ws = Sheets("Sheet4")

    Debug.Print ws.Cells(23, 4).Value
End Sub

Match exact string

"^" For the begining of the line "$" for the end of it. Eg.:

var re = /^abc$/;

Would match "abc" but not "1abc" or "abc1". You can learn more at

Execution failed app:processDebugResources Android Studio

I encountered Execution failed app:processDebugResources Android Studio after upgrading SDK repository. I use Android Studio 1.5.1, target SDK version 23. I was using buildToolsVersion 21.0.1 previously, changing buildToolsVersion to 21.1.2 solved my problem.

You might want to how I find version 21.1.2 suitable. It was recommended by Android Studio after successfully upgraded my SDK.

enter image description here

After changing buildToolsVersion to 21.1.2 (refer to my version settings below), you need to synchronize your Gradle build mechanism.

apply plugin: ''

android {
    compileSdkVersion 23
    buildToolsVersion "21.1.2"

    defaultConfig {
        applicationId "mm.weboffice"
        minSdkVersion 14
        targetSdkVersion 23
        versionCode 1
        versionName "1.0"
    buildTypes {
        release {
            minifyEnabled false
            proguardFiles getDefaultProguardFile('proguard-android.txt'), ''

dependencies {
    compile fileTree(dir: 'libs', include: ['*.jar'])
    compile ''
    compile ''
    compile ''
    compile ''
    compile ''

Android Studio will prompt you to sync Gradle or you can go to "menubar > File > Synchronize" to trigger synchronization manually. Android Studio will rebuild your project after the synchronization.

enter image description here

I know there are many issues with the SDK database and configuration, my proposed solution may not fix all problems. But if you encounter the similar error after upgrading SDK repository, I hope my post solve your hassle. Good luck!

org.hibernate.MappingException: Unknown entity: annotations.Users

Problem occurs because of the entry mapping class="annotations.Users" in hibernate.cfg.xml remove that line then it will be work.

I had the same issue. When I removed the above line then it was working fine for me.

How to shift a column in Pandas DataFrame

In [18]: a
   x1  x2
0   0   5
1   1   6
2   2   7
3   3   8
4   4   9

In [19]: a['x2'] = a.x2.shift(1)

In [20]: a
   x1  x2
0   0 NaN
1   1   5
2   2   6
3   3   7
4   4   8

Loop through array of values with Arrow Function

In short:

someValues.forEach((element) => {

If you care about index, then second parameter can be passed to receive the index of current element:

someValues.forEach((element, index) => {
    console.log(`Current index: ${index}`);

Refer here to know more about Array of ES6:

Can constructors throw exceptions in Java?

Yes, they can throw exceptions. If so, they will only be partially initialized and if non-final, subject to attack.

The following is from the Secure Coding Guidelines 2.0.

Partially initialized instances of a non-final class can be accessed via a finalizer attack. The attacker overrides the protected finalize method in a subclass, and attempts to create a new instance of that subclass. This attempt fails (in the above example, the SecurityManager check in ClassLoader's constructor throws a security exception), but the attacker simply ignores any exception and waits for the virtual machine to perform finalization on the partially initialized object. When that occurs the malicious finalize method implementation is invoked, giving the attacker access to this, a reference to the object being finalized. Although the object is only partially initialized, the attacker can still invoke methods on it (thereby circumventing the SecurityManager check).