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Free ASP.Net and/or CSS Themes

Microsoft hired one fo the kids from A List Apart to whip some out. The .Net projects are free of charge for download.

http://msdn.microsoft.com/en-us/asp.net/aa336613.aspx

Algorithm to find Largest prime factor of a number

n = abs(number);
result = 1;
if (n mod 2 == 0) {
  result = 2;
  while (n mod 2 = 0) n /= 2;
}
for(i=3; i<sqrt(n); i+=2) {
  if (n mod i == 0) {
    result = i;
    while (n mod i = 0)  n /= i;
  }
}
return max(n,result)

There are some modulo tests that are superflous, as n can never be divided by 6 if all factors 2 and 3 have been removed. You could only allow primes for i, which is shown in several other answers here.

You could actually intertwine the sieve of Eratosthenes here:

  • First create the list of integers up to sqrt(n).
  • In the for loop mark all multiples of i up to the new sqrt(n) as not prime, and use a while loop instead.
  • set i to the next prime number in the list.

Also see this question.

What is the difference between procedural programming and functional programming?

To expand on Konrad's comment:

As a consequence, a purely functional program always yields the same value for an input, and the order of evaluation is not well-defined;

Because of this, functional code is generally easier to parallelize. Since there are (generally) no side effects of the functions, and they (generally) just act on their arguments, a lot of concurrency issues go away.

Functional programming is also used when you need to be capable of proving your code is correct. This is much harder to do with procedural programming (not easy with functional, but still easier).

Disclaimer: I haven't used functional programming in years, and only recently started looking at it again, so I might not be completely correct here. :)

When do you use the "this" keyword?

I use it anywhere there might be ambiguity (obviously). Not just compiler ambiguity (it would be required in that case), but also ambiguity for someone looking at the code.

What is the best way to prevent session hijacking?

Protect by:

$ip=$_SERVER['REMOTE_ADDER'];
$_SESSEION['ip']=$ip;

Language Books/Tutorials for popular languages

Some books on Java I'd recommend:

For Beginners: Head First Java is an excellent introduction to the language. And I must also mention Head First Design Patterns which is a great resource for learners to grasp what can be quite challenging concepts. The easy-going fun style of these books are ideal for ppl new to programming.

A really thorough, comprehensive book on Java SE is Bruce Eckel's Thinking In Java v4. (At just under 1500 pages it's good for weight-training as well!) For those of us not on fat bank-bonuses there are older versions available for free download.

Of course, as many ppl have already mentioned, Josh Bloch's Effective Java v2 is an essential part of any Java developer's library.

How do I perform a Perl substitution on a string while keeping the original?

Under use strict, say:

(my $new = $original) =~ s/foo/bar/;

instead.

How to decode viewstate

Use Fiddler and grab the view state in the response and paste it into the bottom left text box then decode.

What's the best mock framework for Java?

We are heavily using EasyMock and EasyMock Class Extension at work and are pretty happy with it. It basically gives you everything you need. Take a look at the documentation, there's a very nice example which shows you all the features of EasyMock.

How to download a file over HTTP?

If speed matters to you, I made a small performance test for the modules urllib and wget, and regarding wget I tried once with status bar and once without. I took three different 500MB files to test with (different files- to eliminate the chance that there is some caching going on under the hood). Tested on debian machine, with python2.

First, these are the results (they are similar in different runs):

$ python wget_test.py 
urlretrive_test : starting
urlretrive_test : 6.56
==============
wget_no_bar_test : starting
wget_no_bar_test : 7.20
==============
wget_with_bar_test : starting
100% [......................................................................] 541335552 / 541335552
wget_with_bar_test : 50.49
==============

The way I performed the test is using "profile" decorator. This is the full code:

import wget
import urllib
import time
from functools import wraps

def profile(func):
    @wraps(func)
    def inner(*args):
        print func.__name__, ": starting"
        start = time.time()
        ret = func(*args)
        end = time.time()
        print func.__name__, ": {:.2f}".format(end - start)
        return ret
    return inner

url1 = 'http://host.com/500a.iso'
url2 = 'http://host.com/500b.iso'
url3 = 'http://host.com/500c.iso'

def do_nothing(*args):
    pass

@profile
def urlretrive_test(url):
    return urllib.urlretrieve(url)

@profile
def wget_no_bar_test(url):
    return wget.download(url, out='/tmp/', bar=do_nothing)

@profile
def wget_with_bar_test(url):
    return wget.download(url, out='/tmp/')

urlretrive_test(url1)
print '=============='
time.sleep(1)

wget_no_bar_test(url2)
print '=============='
time.sleep(1)

wget_with_bar_test(url3)
print '=============='
time.sleep(1)

urllib seems to be the fastest

Best practices for catching and re-throwing .NET exceptions

Actually, there are some situations which the throw statment will not preserve the StackTrace information. For example, in the code below:

try
{
  int i = 0;
  int j = 12 / i; // Line 47
  int k = j + 1;
}
catch
{
  // do something
  // ...
  throw; // Line 54
}

The StackTrace will indicate that line 54 raised the exception, although it was raised at line 47.

Unhandled Exception: System.DivideByZeroException: Attempted to divide by zero.
   at Program.WithThrowIncomplete() in Program.cs:line 54
   at Program.Main(String[] args) in Program.cs:line 106

In situations like the one described above, there are two options to preseve the original StackTrace:

Calling the Exception.InternalPreserveStackTrace

As it is a private method, it has to be invoked by using reflection:

private static void PreserveStackTrace(Exception exception)
{
  MethodInfo preserveStackTrace = typeof(Exception).GetMethod("InternalPreserveStackTrace",
    BindingFlags.Instance | BindingFlags.NonPublic);
  preserveStackTrace.Invoke(exception, null);
}

I has a disadvantage of relying on a private method to preserve the StackTrace information. It can be changed in future versions of .NET Framework. The code example above and proposed solution below was extracted from Fabrice MARGUERIE weblog.

Calling Exception.SetObjectData

The technique below was suggested by Anton Tykhyy as answer to In C#, how can I rethrow InnerException without losing stack trace question.

static void PreserveStackTrace (Exception e) 
{ 
  var ctx = new StreamingContext  (StreamingContextStates.CrossAppDomain) ; 
  var mgr = new ObjectManager     (null, ctx) ; 
  var si  = new SerializationInfo (e.GetType (), new FormatterConverter ()) ; 

  e.GetObjectData    (si, ctx)  ; 
  mgr.RegisterObject (e, 1, si) ; // prepare for SetObjectData 
  mgr.DoFixups       ()         ; // ObjectManager calls SetObjectData 

  // voila, e is unmodified save for _remoteStackTraceString 
} 

Although, it has the advantage of relying in public methods only it also depends on the following exception constructor (which some exceptions developed by 3rd parties do not implement):

protected Exception(
    SerializationInfo info,
    StreamingContext context
)

In my situation, I had to choose the first approach, because the exceptions raised by a 3rd-party library I was using didn't implement this constructor.

Format numbers to strings in Python

str() in python on an integer will not print any decimal places.

If you have a float that you want to ignore the decimal part, then you can use str(int(floatValue)).

Perhaps the following code will demonstrate:

>>> str(5)
'5'
>>> int(8.7)
8

How can I develop for iPhone using a Windows development machine?

Develop iOS Apps on Windows With Cross-Platform Tools

Cross-platform tools are awesome: you code your app once, and export it to iOS and Android. That could potentially cut your app development time and cost in half. Several cross-platform tools allow you to develop iOS apps on a Windows PC, or allow you to compile the app if there’s a Mac in your local network.

Well, not so fast…

The cross-platform tool ecosystem is very large. On the one side you have complete Integrated Development Environments (IDEs) like Xamarin, that allow you to build cross-platform apps with C#.

The middle ground is covered by tools like PhoneGap, Cordova, Ionic and Appcelerator, that let you build native apps with HTML5 components. The far end includes smaller platforms like React Native that allow you to write native apps with a JavaScript wrapper.

The one thing that stands out for all cross-platform tools is this: they’re not beginner friendly! It’s much easier to get access to a Mac, learn Swift, and build a simple app, than it is to get started with Xamarin.

Most of the cross-platform tools require you to have a basic understanding of programming, compilation options, and the iOS and Android ecosystems. That’s something you don’t really have as a beginner developer!

Having said that, let’s look at a couple of options:

If you’re familiar with Windows-based development tools and IDEs, and if you already know how to code, it’s worthwhile to check out Xamarin. With Xamarin you code apps in C#, for multiple platforms, using the Mono and MonoTouch frameworks. If you’re familiar with web-based development, check out PhoneGap or Ionic. You’ll feel right at home with HTML 5, CSS and JavaScript. Don’t forget: a native app works different than a website… If you’re familiar with JavaScript, or if you’d rather learn to code JavaScript than Swift, check out React Native. With React Native you can code native apps for iOS and Android using a “wrapper”. Always deliberately choose for cross-platform tools because it’s a smart option, not because you think a native platform language is bad. The fact that one option isn’t right, doesn’t immediately make another option smarter!

If you don’t want to join the proprietary closed Apple universe, don’t forget that many cross-platform tools are operated by equally evil companies like Google, Facebook, Microsoft, Adobe and Amazon.

An often heard argument against cross-platform tools is that they offer limited access to and support for smartphone hardware, and are less “snappy” than their native counterparts. Keep in mind that any cross-platform tool will require you to write platform-specific code at one point, especially if you want to code custom features.

Cleanest Way to Invoke Cross-Thread Events

I've always wondered how costly it is to always assume that invoke is required...

private void OnCoolEvent(CoolObjectEventArgs e)
{
  BeginInvoke((o,e) => /*do work here*/,this, e);
}

Why can't I declare static methods in an interface?

Perhaps a code example would help, I'm going to use C#, but you should be able to follow along.

Lets pretend we have an interface called IPayable

public interface IPayable
{
    public Pay(double amount);
}

Now, we have two concrete classes that implement this interface:

public class BusinessAccount : IPayable
{
    public void Pay(double amount)
    {
        //Logic
    }
}

public class CustomerAccount : IPayable
{
    public void Pay(double amount)
    {
        //Logic
    }
}

Now, lets pretend we have a collection of various accounts, to do this we will use a generic list of the type IPayable

List<IPayable> accountsToPay = new List<IPayable>();
accountsToPay.add(new CustomerAccount());
accountsToPay.add(new BusinessAccount());

Now, we want to pay $50.00 to all those accounts:

foreach (IPayable account in accountsToPay)
{
    account.Pay(50.00);
}

So now you see how interfaces are incredibly useful.

They are used on instantiated objects only. Not on static classes.

If you had made pay static, when looping through the IPayable's in accountsToPay there would be no way to figure out if it should call pay on BusinessAcount or CustomerAccount.

Reading from text file until EOF repeats last line

The EOF pattern needs a prime read to 'bootstrap' the EOF checking process. Consider the empty file will not initially have its EOF set until the first read. The prime read will catch the EOF in this instance and properly skip the loop completely.

What you need to remember here is that you don't get the EOF until the first attempt to read past the available data of the file. Reading the exact amount of data will not flag the EOF.

I should point out if the file was empty your given code would have printed since the EOF will have prevented a value from being set to x on entry into the loop.

  • 0

So add a prime read and move the loop's read to the end:

int x;

iFile >> x; // prime read here
while (!iFile.eof()) {
    cerr << x << endl;
    iFile >> x;
}

.NET - Get protocol, host, and port

Well if you are doing this in Asp.Net or have access to HttpContext.Current.Request I'd say these are easier and more general ways of getting them:

var scheme = Request.Url.Scheme; // will get http, https, etc.
var host = Request.Url.Host; // will get www.mywebsite.com
var port = Request.Url.Port; // will get the port
var path = Request.Url.AbsolutePath; // should get the /pages/page1.aspx part, can't remember if it only get pages/page1.aspx

I hope this helps. :)

What is the difference between #include <filename> and #include "filename"?

The only way to know is to read your implementation's documentation.

In the C standard, section 6.10.2, paragraphs 2 to 4 state:

  • A preprocessing directive of the form

    #include <h-char-sequence> new-line
    

    searches a sequence of implementation-defined places for a header identified uniquely by the specified sequence between the < and > delimiters, and causes the replacement of that directive by the entire contents of the header. How the places are specified or the header identified is implementation-defined.

  • A preprocessing directive of the form

    #include "q-char-sequence" new-line
    

    causes the replacement of that directive by the entire contents of the source file identified by the specified sequence between the " delimiters. The named source file is searched for in an implementation-defined manner. If this search is not supported, or if the search fails, the directive is reprocessed as if it read

    #include <h-char-sequence> new-line
    

    with the identical contained sequence (including > characters, if any) from the original directive.

  • A preprocessing directive of the form

    #include pp-tokens new-line
    

    (that does not match one of the two previous forms) is permitted. The preprocessing tokens after include in the directive are processed just as in normal text. (Each identifier currently defined as a macro name is replaced by its replacement list of preprocessing tokens.) The directive resulting after all replacements shall match one of the two previous forms. The method by which a sequence of preprocessing tokens between a < and a > preprocessing token pair or a pair of " characters is combined into a single header name preprocessing token is implementation-defined.

Definitions:

  • h-char: any member of the source character set except the new-line character and >

  • q-char: any member of the source character set except the new-line character and "

In C++, what is a virtual base class?

Explaining multiple-inheritance with virtual bases requires a knowledge of the C++ object model. And explaining the topic clearly is best done in an article and not in a comment box.

The best, readable explanation I found that solved all my doubts on this subject was this article: http://www.phpcompiler.org/articles/virtualinheritance.html

You really won't need to read anything else on the topic (unless you are a compiler writer) after reading that...

In SQL Server, how do I generate a CREATE TABLE statement for a given table?

If the application you are generating the scripts from is a .NET application, you may want to look into using SMO (Sql Management Objects). Reference this SQL Team link on how to use SMO to script objects.

Dynamically load a JavaScript file

With Promises you can simplify it like this. Loader function:

  const loadCDN = src =>
    new Promise((resolve, reject) => {
      if (document.querySelector(`head > script[src="${src}"]`) !== null) return resolve()
      const script = document.createElement("script")
      script.src = src
      script.async = true
      document.head.appendChild(script)
      script.onload = resolve
      script.onerror = reject
    })

Usage (async/await):

await loadCDN("https://.../script.js")

Usage (Promise):

loadCDN("https://.../script.js").then(res => {}).catch(err => {})

NOTE: there was one similar solution but it doesn't check if the script is already loaded and loads the script each time. This one checks src property.

Which .NET Dependency Injection frameworks are worth looking into?

The great thing about C# is that it is following a path beaten by years of Java developers before it. So, my advice, generally speaking when looking for tools of this nature, is to look for the solid Java answer and see if there exists a .NET adaptation yet.

So when it comes to DI (and there are so many options out there, this really is a matter of taste) is Spring.NET. Additionally, it's always wise to research the people behind projects. I have no issue suggesting SourceGear products for source control (outside of using them) because I have respect for Eric Sink. I have seen Mark Pollack speak and what can I say, the guy just gets it.

In the end, there are a lot of DI frameworks and your best bet is to do some sample projects with a few of them and make an educated choice.

Good luck!

Simplest way to profile a PHP script

For benchmarking, like in your example, I use the pear Benchmark package. You set markers for measuring. The class also provides a few presentation helpers, or you can process the data as you see fit.

I actually have it wrapped in another class with a __destruct method. When a script exits, the output is logged via log4php to syslog, so I have a lot of performance data to work from.

Most efficient way to concatenate strings?

From this MSDN article:

There is some overhead associated with creating a StringBuilder object, both in time and memory. On a machine with fast memory, a StringBuilder becomes worthwhile if you're doing about five operations. As a rule of thumb, I would say 10 or more string operations is a justification for the overhead on any machine, even a slower one.

So if you trust MSDN go with StringBuilder if you have to do more than 10 strings operations/concatenations - otherwise simple string concat with '+' is fine.

List of standard lengths for database fields

UK Government Data Standards Catalogue details the UK standards for this kind of thing. It suggests 35 characters for each of Given Name and Family Name, or 70 characters for a single field to hold the Full Name, and 255 characters for an email address. Amongst other things..

Recommended SQL database design for tags or tagging

Three tables (one for storing all items, one for all tags, and one for the relation between the two), properly indexed, with foreign keys set running on a proper database, should work well and scale properly.

Table: Item
Columns: ItemID, Title, Content

Table: Tag
Columns: TagID, Title

Table: ItemTag
Columns: ItemID, TagID

How do you clear a stringstream variable?

my 2 cents:

this seemed to work for me in xcode and dev-c++, I had a program in the form of a menu that if executed iteratively as per the request of a user will fill up a stringstream variable which would work ok the first time the code would run but would not clear the stringstream the next time the user will run the same code. but the two lines of code below finally cleared up the stringstream variable everytime before filling up the string variable. (2 hours of trial and error and google searches), btw, using each line on their own would not do the trick.

//clear the stringstream variable

sstm.str("");
sstm.clear();

//fill up the streamstream variable
sstm << "crap" << "morecrap";

Image UriSource and Data Binding

WPF has built-in converters for certain types. If you bind the Image's Source property to a string or Uri value, under the hood WPF will use an ImageSourceConverter to convert the value to an ImageSource.

So

<Image Source="{Binding ImageSource}"/>

would work if the ImageSource property was a string representation of a valid URI to an image.

You can of course roll your own Binding converter:

public class ImageConverter : IValueConverter
{
    public object Convert(
        object value, Type targetType, object parameter, CultureInfo culture)
    {
        return new BitmapImage(new Uri(value.ToString()));
    }

    public object ConvertBack(
        object value, Type targetType, object parameter, CultureInfo culture)
    {
        throw new NotSupportedException();
    }
}

and use it like this:

<Image Source="{Binding ImageSource, Converter={StaticResource ImageConverter}}"/>

List of macOS text editors and code editors

I used BBEdit for years, but recently converted to Panic's Coda.

I love Coda. It does everything that I need and now that I've begun programming plug-ins for it, it's become a far more rich tool. The support team are responsive and the community that is growing around it is fantastic. There is still a lot of room for improvement, but that's the cool thing about being part of the kind of community that surrounds it; you have a say in what that improvement is.

Panic - Coda

How do I use 3DES encryption/decryption in Java?

Your code was fine except for the Base 64 encoding bit (which you mentioned was a test), the reason the output may not have made sense is that you were displaying a raw byte array (doing toString() on a byte array returns its internal Java reference, not the String representation of the contents). Here's a version that's just a teeny bit cleaned up and which prints "kyle boon" as the decoded string:

import java.security.MessageDigest;
import java.util.Arrays;

import javax.crypto.Cipher;
import javax.crypto.SecretKey;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;

public class TripleDESTest {

    public static void main(String[] args) throws Exception {

        String text = "kyle boon";

        byte[] codedtext = new TripleDESTest().encrypt(text);
        String decodedtext = new TripleDESTest().decrypt(codedtext);

        System.out.println(codedtext); // this is a byte array, you'll just see a reference to an array
        System.out.println(decodedtext); // This correctly shows "kyle boon"
    }

    public byte[] encrypt(String message) throws Exception {
        final MessageDigest md = MessageDigest.getInstance("md5");
        final byte[] digestOfPassword = md.digest("HG58YZ3CR9"
                .getBytes("utf-8"));
        final byte[] keyBytes = Arrays.copyOf(digestOfPassword, 24);
        for (int j = 0, k = 16; j < 8;) {
            keyBytes[k++] = keyBytes[j++];
        }

        final SecretKey key = new SecretKeySpec(keyBytes, "DESede");
        final IvParameterSpec iv = new IvParameterSpec(new byte[8]);
        final Cipher cipher = Cipher.getInstance("DESede/CBC/PKCS5Padding");
        cipher.init(Cipher.ENCRYPT_MODE, key, iv);

        final byte[] plainTextBytes = message.getBytes("utf-8");
        final byte[] cipherText = cipher.doFinal(plainTextBytes);
        // final String encodedCipherText = new sun.misc.BASE64Encoder()
        // .encode(cipherText);

        return cipherText;
    }

    public String decrypt(byte[] message) throws Exception {
        final MessageDigest md = MessageDigest.getInstance("md5");
        final byte[] digestOfPassword = md.digest("HG58YZ3CR9"
                .getBytes("utf-8"));
        final byte[] keyBytes = Arrays.copyOf(digestOfPassword, 24);
        for (int j = 0, k = 16; j < 8;) {
            keyBytes[k++] = keyBytes[j++];
        }

        final SecretKey key = new SecretKeySpec(keyBytes, "DESede");
        final IvParameterSpec iv = new IvParameterSpec(new byte[8]);
        final Cipher decipher = Cipher.getInstance("DESede/CBC/PKCS5Padding");
        decipher.init(Cipher.DECRYPT_MODE, key, iv);

        // final byte[] encData = new
        // sun.misc.BASE64Decoder().decodeBuffer(message);
        final byte[] plainText = decipher.doFinal(message);

        return new String(plainText, "UTF-8");
    }
}

Where can I find decent visio templates/diagrams for software architecture?

There should be templates already included in Visio 2007 for software architecture but you might want to check out Visio 2007 templates.

MyISAM versus InnoDB

Also check out some drop-in replacements for MySQL itself:

MariaDB

http://mariadb.org/

MariaDB is a database server that offers drop-in replacement functionality for MySQL. MariaDB is built by some of the original authors of MySQL, with assistance from the broader community of Free and open source software developers. In addition to the core functionality of MySQL, MariaDB offers a rich set of feature enhancements including alternate storage engines, server optimizations, and patches.

Percona Server

https://launchpad.net/percona-server

An enhanced drop-in replacement for MySQL, with better performance, improved diagnostics, and added features.

What's the best way to parse command line arguments?

Just in case you might need to, this may help if you need to grab unicode arguments on Win32 (2K, XP etc):


from ctypes import *

def wmain(argc, argv):
    print argc
    for i in argv:
        print i
    return 0

def startup():
    size = c_int()
    ptr = windll.shell32.CommandLineToArgvW(windll.kernel32.GetCommandLineW(), byref(size))
    ref = c_wchar_p * size.value
    raw = ref.from_address(ptr)
    args = [arg for arg in raw]
    windll.kernel32.LocalFree(ptr)
    exit(wmain(len(args), args))
startup()

How do you embed binary data in XML?

You could encode the binary data using base64 and put it into a Base64 element; the below article is a pretty good one on the subject.

Handling Binary Data in XML Documents

How to request a random row in SQL?

For MySQL to get random record

 SELECT name
  FROM random AS r1 JOIN
       (SELECT (RAND() *
                     (SELECT MAX(id)
                        FROM random)) AS id)
        AS r2
 WHERE r1.id >= r2.id
 ORDER BY r1.id ASC
 LIMIT 1

More detail http://jan.kneschke.de/projects/mysql/order-by-rand/

Transpose/Unzip Function (inverse of zip)?

Consider using more_itertools.unzip:

>>> from more_itertools import unzip
>>> original = [('a', 1), ('b', 2), ('c', 3), ('d', 4)]
>>> [list(x) for x in unzip(original)]
[['a', 'b', 'c', 'd'], [1, 2, 3, 4]]     

Build a basic Python iterator

There are four ways to build an iterative function:

Examples:

# generator
def uc_gen(text):
    for char in text.upper():
        yield char

# generator expression
def uc_genexp(text):
    return (char for char in text.upper())

# iterator protocol
class uc_iter():
    def __init__(self, text):
        self.text = text.upper()
        self.index = 0
    def __iter__(self):
        return self
    def __next__(self):
        try:
            result = self.text[self.index]
        except IndexError:
            raise StopIteration
        self.index += 1
        return result

# getitem method
class uc_getitem():
    def __init__(self, text):
        self.text = text.upper()
    def __getitem__(self, index):
        return self.text[index]

To see all four methods in action:

for iterator in uc_gen, uc_genexp, uc_iter, uc_getitem:
    for ch in iterator('abcde'):
        print(ch, end=' ')
    print()

Which results in:

A B C D E
A B C D E
A B C D E
A B C D E

Note:

The two generator types (uc_gen and uc_genexp) cannot be reversed(); the plain iterator (uc_iter) would need the __reversed__ magic method (which, according to the docs, must return a new iterator, but returning self works (at least in CPython)); and the getitem iteratable (uc_getitem) must have the __len__ magic method:

    # for uc_iter we add __reversed__ and update __next__
    def __reversed__(self):
        self.index = -1
        return self
    def __next__(self):
        try:
            result = self.text[self.index]
        except IndexError:
            raise StopIteration
        self.index += -1 if self.index < 0 else +1
        return result

    # for uc_getitem
    def __len__(self)
        return len(self.text)

To answer Colonel Panic's secondary question about an infinite lazily evaluated iterator, here are those examples, using each of the four methods above:

# generator
def even_gen():
    result = 0
    while True:
        yield result
        result += 2


# generator expression
def even_genexp():
    return (num for num in even_gen())  # or even_iter or even_getitem
                                        # not much value under these circumstances

# iterator protocol
class even_iter():
    def __init__(self):
        self.value = 0
    def __iter__(self):
        return self
    def __next__(self):
        next_value = self.value
        self.value += 2
        return next_value

# getitem method
class even_getitem():
    def __getitem__(self, index):
        return index * 2

import random
for iterator in even_gen, even_genexp, even_iter, even_getitem:
    limit = random.randint(15, 30)
    count = 0
    for even in iterator():
        print even,
        count += 1
        if count >= limit:
            break
    print

Which results in (at least for my sample run):

0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38 40 42 44 46 48 50 52 54
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32 34 36 38
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30
0 2 4 6 8 10 12 14 16 18 20 22 24 26 28 30 32

How to choose which one to use? This is mostly a matter of taste. The two methods I see most often are generators and the iterator protocol, as well as a hybrid (__iter__ returning a generator).

Generator expressions are useful for replacing list comprehensions (they are lazy and so can save on resources).

If one needs compatibility with earlier Python 2.x versions use __getitem__.

What is the correct way to create a single-instance WPF application?

Normally, this is the code I use for single-instance Windows Forms applications:

[STAThread]
public static void Main()
{
    String assemblyName = Assembly.GetExecutingAssembly().GetName().Name;

    using (Mutex mutex = new Mutex(false, assemblyName))
    {
        if (!mutex.WaitOne(0, false))
        {
            Boolean shownProcess = false;
            Process currentProcess = Process.GetCurrentProcess();

            foreach (Process process in Process.GetProcessesByName(currentProcess.ProcessName))
            {
                if (!process.Id.Equals(currentProcess.Id) && process.MainModule.FileName.Equals(currentProcess.MainModule.FileName) && !process.MainWindowHandle.Equals(IntPtr.Zero))
                {
                    IntPtr windowHandle = process.MainWindowHandle;

                    if (NativeMethods.IsIconic(windowHandle))
                        NativeMethods.ShowWindow(windowHandle, ShowWindowCommand.Restore);

                    NativeMethods.SetForegroundWindow(windowHandle);

                    shownProcess = true;
                }
            }

            if (!shownProcess)
                MessageBox.Show(String.Format(CultureInfo.CurrentCulture, "An instance of {0} is already running!", assemblyName), assemblyName, MessageBoxButtons.OK, MessageBoxIcon.Asterisk, MessageBoxDefaultButton.Button1, (MessageBoxOptions)0);
        }
        else
        {
            Application.EnableVisualStyles();
            Application.SetCompatibleTextRenderingDefault(false);
            Application.Run(new Form());
        }
    }
}

Where native components are:

[DllImport("User32.dll", CharSet = CharSet.Unicode, ExactSpelling = true, SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
internal static extern Boolean IsIconic([In] IntPtr windowHandle);

[DllImport("User32.dll", CharSet = CharSet.Unicode, ExactSpelling = true, SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
internal static extern Boolean SetForegroundWindow([In] IntPtr windowHandle);

[DllImport("User32.dll", CharSet = CharSet.Unicode, ExactSpelling = true, SetLastError = true)]
[return: MarshalAs(UnmanagedType.Bool)]
internal static extern Boolean ShowWindow([In] IntPtr windowHandle, [In] ShowWindowCommand command);

public enum ShowWindowCommand : int
{
    Hide                   = 0x0,
    ShowNormal             = 0x1,
    ShowMinimized          = 0x2,
    ShowMaximized          = 0x3,
    ShowNormalNotActive    = 0x4,
    Minimize               = 0x6,
    ShowMinimizedNotActive = 0x7,
    ShowCurrentNotActive   = 0x8,
    Restore                = 0x9,
    ShowDefault            = 0xA,
    ForceMinimize          = 0xB
}

Is there a simple, elegant way to define singletons?

A slightly different approach to implement the singleton in Python is the borg pattern by Alex Martelli (Google employee and Python genius).

class Borg:
    __shared_state = {}
    def __init__(self):
        self.__dict__ = self.__shared_state

So instead of forcing all instances to have the same identity, they share state.

How do you configure an OpenFileDialog to select folders?

First Solution

I developed this as a cleaned up version of .NET Win 7-style folder select dialog by Bill Seddon of lyquidity.com (I have no affiliation). (I learned of his code from another answer on this page). I wrote my own because his solution requires an additional Reflection class that isn't needed for this focused purpose, uses exception-based flow control, doesn't cache the results of its reflection calls. Note that the nested static VistaDialog class is so that its static reflection variables don't try to get populated if the Show method is never called. It falls back to the pre-Vista dialog if not in a high enough Windows version. Should work in Windows 7, 8, 9, 10 and higher (theoretically).

using System;
using System.Reflection;
using System.Windows.Forms;

namespace ErikE.Shuriken {
    /// <summary>
    /// Present the Windows Vista-style open file dialog to select a folder. Fall back for older Windows Versions
    /// </summary>
    public class FolderSelectDialog {
        private string _initialDirectory;
        private string _title;
        private string _fileName = "";

        public string InitialDirectory {
            get { return string.IsNullOrEmpty(_initialDirectory) ? Environment.CurrentDirectory : _initialDirectory; }
            set { _initialDirectory = value; }
        }
        public string Title {
            get { return _title ?? "Select a folder"; }
            set { _title = value; }
        }
        public string FileName { get { return _fileName; } }

        public bool Show() { return Show(IntPtr.Zero); }

        /// <param name="hWndOwner">Handle of the control or window to be the parent of the file dialog</param>
        /// <returns>true if the user clicks OK</returns>
        public bool Show(IntPtr hWndOwner) {
            var result = Environment.OSVersion.Version.Major >= 6
                ? VistaDialog.Show(hWndOwner, InitialDirectory, Title)
                : ShowXpDialog(hWndOwner, InitialDirectory, Title);
            _fileName = result.FileName;
            return result.Result;
        }

        private struct ShowDialogResult {
            public bool Result { get; set; }
            public string FileName { get; set; }
        }

        private static ShowDialogResult ShowXpDialog(IntPtr ownerHandle, string initialDirectory, string title) {
            var folderBrowserDialog = new FolderBrowserDialog {
                Description = title,
                SelectedPath = initialDirectory,
                ShowNewFolderButton = false
            };
            var dialogResult = new ShowDialogResult();
            if (folderBrowserDialog.ShowDialog(new WindowWrapper(ownerHandle)) == DialogResult.OK) {
                dialogResult.Result = true;
                dialogResult.FileName = folderBrowserDialog.SelectedPath;
            }
            return dialogResult;
        }

        private static class VistaDialog {
            private const string c_foldersFilter = "Folders|\n";

            private const BindingFlags c_flags = BindingFlags.Instance | BindingFlags.Public | BindingFlags.NonPublic;
            private readonly static Assembly s_windowsFormsAssembly = typeof(FileDialog).Assembly;
            private readonly static Type s_iFileDialogType = s_windowsFormsAssembly.GetType("System.Windows.Forms.FileDialogNative+IFileDialog");
            private readonly static MethodInfo s_createVistaDialogMethodInfo = typeof(OpenFileDialog).GetMethod("CreateVistaDialog", c_flags);
            private readonly static MethodInfo s_onBeforeVistaDialogMethodInfo = typeof(OpenFileDialog).GetMethod("OnBeforeVistaDialog", c_flags);
            private readonly static MethodInfo s_getOptionsMethodInfo = typeof(FileDialog).GetMethod("GetOptions", c_flags);
            private readonly static MethodInfo s_setOptionsMethodInfo = s_iFileDialogType.GetMethod("SetOptions", c_flags);
            private readonly static uint s_fosPickFoldersBitFlag = (uint) s_windowsFormsAssembly
                .GetType("System.Windows.Forms.FileDialogNative+FOS")
                .GetField("FOS_PICKFOLDERS")
                .GetValue(null);
            private readonly static ConstructorInfo s_vistaDialogEventsConstructorInfo = s_windowsFormsAssembly
                .GetType("System.Windows.Forms.FileDialog+VistaDialogEvents")
                .GetConstructor(c_flags, null, new[] { typeof(FileDialog) }, null);
            private readonly static MethodInfo s_adviseMethodInfo = s_iFileDialogType.GetMethod("Advise");
            private readonly static MethodInfo s_unAdviseMethodInfo = s_iFileDialogType.GetMethod("Unadvise");
            private readonly static MethodInfo s_showMethodInfo = s_iFileDialogType.GetMethod("Show");

            public static ShowDialogResult Show(IntPtr ownerHandle, string initialDirectory, string title) {
                var openFileDialog = new OpenFileDialog {
                    AddExtension = false,
                    CheckFileExists = false,
                    DereferenceLinks = true,
                    Filter = c_foldersFilter,
                    InitialDirectory = initialDirectory,
                    Multiselect = false,
                    Title = title
                };

                var iFileDialog = s_createVistaDialogMethodInfo.Invoke(openFileDialog, new object[] { });
                s_onBeforeVistaDialogMethodInfo.Invoke(openFileDialog, new[] { iFileDialog });
                s_setOptionsMethodInfo.Invoke(iFileDialog, new object[] { (uint) s_getOptionsMethodInfo.Invoke(openFileDialog, new object[] { }) | s_fosPickFoldersBitFlag });
                var adviseParametersWithOutputConnectionToken = new[] { s_vistaDialogEventsConstructorInfo.Invoke(new object[] { openFileDialog }), 0U };
                s_adviseMethodInfo.Invoke(iFileDialog, adviseParametersWithOutputConnectionToken);

                try {
                    int retVal = (int) s_showMethodInfo.Invoke(iFileDialog, new object[] { ownerHandle });
                    return new ShowDialogResult {
                        Result = retVal == 0,
                        FileName = openFileDialog.FileName
                    };
                }
                finally {
                    s_unAdviseMethodInfo.Invoke(iFileDialog, new[] { adviseParametersWithOutputConnectionToken[1] });
                }
            }
        }

        // Wrap an IWin32Window around an IntPtr
        private class WindowWrapper : IWin32Window {
            private readonly IntPtr _handle;
            public WindowWrapper(IntPtr handle) { _handle = handle; }
            public IntPtr Handle { get { return _handle; } }
        }
    }
}

It is used like so in a Windows Form:

var dialog = new FolderSelectDialog {
    InitialDirectory = musicFolderTextBox.Text,
    Title = "Select a folder to import music from"
};
if (dialog.Show(Handle)) {
    musicFolderTextBox.Text = dialog.FileName;
}

You can of course play around with its options and what properties it exposes. For example, it allows multiselect in the Vista-style dialog.

Second Solution

Simon Mourier gave an answer that shows how to do the exact same job using interop against the Windows API directly, though his version would have to be supplemented to use the older style dialog if in an older version of Windows. Unfortunately, I hadn't found his post yet when I worked up my solution. Name your poison!

How to insert a line break in a SQL Server VARCHAR/NVARCHAR string

This is always cool, because when you get exported lists from, say Oracle, then you get records spanning several lines, which in turn can be interesting for, say, cvs files, so beware.

Anyhow, Rob's answer is good, but I would advise using something else than @, try a few more, like §§@@§§ or something, so it will have a chance for some uniqueness. (But still, remember the length of the varchar/nvarchar field you are inserting into..)

Is there an "exists" function for jQuery?

I'm using this:

    $.fn.ifExists = function(fn) {
      if (this.length) {
        $(fn(this));
      }
    };
    $("#element").ifExists( 
      function($this){
        $this.addClass('someClass').animate({marginTop:20},function(){alert('ok')});               
      }
    ); 

Execute the chain only if a jQuery element exist - http://jsfiddle.net/andres_314/vbNM3/2/

Get file version in PowerShell

This is based on the other answers, but is exactly what I was after:

(Get-Command C:\Path\YourFile.Dll).FileVersionInfo.FileVersion

Difference between the Apache HTTP Server and Apache Tomcat?

If you are using java technology(Servlet/JSP) for making web application you will probably use Apache Tomcat. However, if you are using other technologies like Perl, PHP or ruby, its better(easier) to use Apache HTTP Server.

How do I tell Maven to use the latest version of a dependency?

If you want Maven should use the latest version of a dependency, then you can use Versions Maven Plugin and how to use this plugin, Tim has already given a good answer, follow his answer.

But as a developer, I will not recommend this type of practices. WHY?

answer to why is already given by Pascal Thivent in the comment of the question

I really don't recommend this practice (nor using version ranges) for the sake of build reproducibility. A build that starts to suddenly fail for an unknown reason is way more annoying than updating manually a version number.

I will recommend this type of practice:

<properties>
    <spring.version>3.1.2.RELEASE</spring.version>
</properties>

<dependencies>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-core</artifactId>
        <version>${spring.version}</version>
    </dependency>

    <dependency>
        <groupId>org.springframework</groupId>
        <artifactId>spring-context</artifactId>
        <version>${spring.version}</version>
    </dependency>

</dependencies>

it is easy to maintain and easy to debug. You can update your POM in no time.

What is a reasonable length limit on person "Name" fields?

depending on who is going to be using your database, for example African names will do with varchar(20) for last name and first name separated. however it is different from nation to nation but for the sake saving your database resources and memory, separate last name and first name fields and use varchar(30) think that will work.

SQL Server: Get data for only the past year

GETDATE() returns current date and time.

If last year starts in midnight of current day last year (like in original example) you should use something like:

DECLARE @start datetime
SET @start = dbo.getdatewithouttime(DATEADD(year, -1, GETDATE())) -- cut time (hours, minutes, ect.) --  getdatewithouttime() function doesn't exist in MS SQL -- you have to write one
SELECT column1, column2, ..., columnN FROM table WHERE date >= @start

Can Windows' built-in ZIP compression be scripted?

Here'a my attempt to summarize built-in capabilities windows for compression and uncompression - How can I compress (/ zip ) and uncompress (/ unzip ) files and folders with batch file without using any external tools?

with a few given solutions that should work on almost every windows machine.

As regards to the shell.application and WSH I preferred the jscript as it allows a hybrid batch/jscript file (with .bat extension) that not require temp files.I've put unzip and zip capabilities in one file plus a few more features.

Boolean Field in Oracle

To use the least amount of space you should use a CHAR field constrained to 'Y' or 'N'. Oracle doesn't support BOOLEAN, BIT, or TINYINT data types, so CHAR's one byte is as small as you can get.

JavaScript and Threads

There is no true multi-threading in Javascript, but you can get asynchronous behavior using setTimeout() and asynchronous AJAX requests.

What exactly are you trying to accomplish?

How do I fire an event when a iframe has finished loading in jQuery?

Using both jquery Load and Ready neither seemed to really match when the iframe was TRULY ready.

I ended up doing something like this

$('#iframe').ready(function () {
    $("#loader").fadeOut(2500, function (sender) {
        $(sender).remove();
    });
});

Where #loader is an absolutely positioned div over top the iframe with a spinner gif.

How to submit a form when the return key is pressed?

Use the <button> tag. From the W3C standard:

Buttons created with the BUTTON element function just like buttons created with the INPUT element, but they offer richer rendering possibilities: the BUTTON element may have content. For example, a BUTTON element that contains an image functions like and may resemble an INPUT element whose type is set to "image", but the BUTTON element type allows content.

Basically there is another tag, <button>, which requires no javascript, that also can submit a form. It can be styled much in the way of a <div> tag (including <img /> inside the button tag). The buttons from the <input /> tag are not nearly as flexible.

<button type="submit">
    <img src="my-icon.png" />
    Clicking will submit the form
</button>

There are three types to set on the <button>; they map to the <input> button types.

<button type="submit">Will submit the form</button>
<button type="reset">Will reset the form</button>
<button type="button">Will do nothing; add javascript onclick hooks</button>

Standards

I use <button> tags with and a bit of styling to get colorful and functional form buttons. Note that it's possible to write css for, for example, <a class="button"> links share to styling with the <button> element.

How to catch SQLServer timeout exceptions

I am not sure but when we have execute time out or command time out The client sends an "ABORT" to SQL Server then simply abandons the query processing. No transaction is rolled back, no locks are released. to solve this problem I Remove transaction in Stored-procedure and use SQL Transaction in my .Net Code To manage sqlException

Cannot access a disposed object - How to fix?

Another place you could stop the timer is the FormClosing event - this happens before the form is actually closed, so is a good place to stop things before they might access unavailable resources.

How to create an exit message

If you want to denote an actual error in your code, you could raise a RuntimeError exception:

raise RuntimeError, 'Message goes here'

This will print a stacktrace, the type of the exception being raised and the message that you provided. Depending on your users, a stacktrace might be too scary, and the actual message might get lost in the noise. On the other hand, if you die because of an actual error, a stacktrace will give you additional information for debugging.

How can I cast int to enum?

This parses integers or strings to a target enum with partial matching in .NET 4.0 using generics like in Tawani's utility class. I am using it to convert command-line switch variables which may be incomplete. Since an enum cannot be null, you should logically provide a default value. It can be called like this:

var result = EnumParser<MyEnum>.Parse(valueToParse, MyEnum.FirstValue);

Here's the code:

using System;

public class EnumParser<T> where T : struct
{
    public static T Parse(int toParse, T defaultVal)
    {
        return Parse(toParse + "", defaultVal);
    }
    public static T Parse(string toParse, T defaultVal)
    {
        T enumVal = defaultVal;
        if (defaultVal is Enum && !String.IsNullOrEmpty(toParse))
        {
            int index;
            if (int.TryParse(toParse, out index))
            {
                Enum.TryParse(index + "", out enumVal);
            }
            else
            {
                if (!Enum.TryParse<T>(toParse + "", true, out enumVal))
                {
                    MatchPartialName(toParse, ref enumVal);
                }
            }
        }
        return enumVal;
    }

    public static void MatchPartialName(string toParse, ref T enumVal)
    {
        foreach (string member in enumVal.GetType().GetEnumNames())
        {
            if (member.ToLower().Contains(toParse.ToLower()))
            {
                if (Enum.TryParse<T>(member + "", out enumVal))
                {
                    break;
                }
            }
        }
    }
}

FYI: The question was about integers, which nobody mentioned will also explicitly convert in Enum.TryParse()

Best GUI designer for eclipse?

It's not free or open source. But you can give Intellij Idea's SWING GUI designer a try.

Converting bool to text in C++

Use boolalpha to print bool to string.

std::cout << std::boolalpha << b << endl;
std::cout << std::noboolalpha << b << endl;

C++ Reference

What are the differences between delegates and events?

What a great misunderstanding between events and delegates!!! A delegate specifies a TYPE (such as a class, or an interface does), whereas an event is just a kind of MEMBER (such as fields, properties, etc). And, just like any other kind of member an event also has a type. Yet, in the case of an event, the type of the event must be specified by a delegate. For instance, you CANNOT declare an event of a type defined by an interface.

Concluding, we can make the following Observation: the type of an event MUST be defined by a delegate. This is the main relation between an event and a delegate and is described in the section II.18 Defining events of ECMA-335 (CLI) Partitions I to VI:

In typical usage, the TypeSpec (if present) identifies a delegate whose signature matches the arguments passed to the event’s fire method.

However, this fact does NOT imply that an event uses a backing delegate field. In truth, an event may use a backing field of any different data structure type of your choice. If you implement an event explicitly in C#, you are free to choose the way you store the event handlers (note that event handlers are instances of the type of the event, which in turn is mandatorily a delegate type---from the previous Observation). But, you can store those event handlers (which are delegate instances) in a data structure such as a List or a Dictionary or any other else, or even in a backing delegate field. But don’t forget that it is NOT mandatory that you use a delegate field.

Getting ssh to execute a command in the background on target machine

I just wanted to show a working example that you can cut and paste:

ssh REMOTE "sh -c \"(nohup sleep 30; touch nohup-exit) > /dev/null &\""

Good Free Alternative To MS Access

Of the Free Software alternatives these haven't been mentioned yet:

I'd also keep an eye on what DB RAD tools the Flex/Air community is coming up with, since with those tools it's possible to get unified desktop and web interfaces.

Best JavaScript compressor

Here's the source code of an HttpHandler which does that, maybe it'll help you

Passing $_POST values with cURL

Another simple PHP example of using cURL:

<?php
    $ch = curl_init();                    // Initiate cURL
    $url = "http://www.somesite.com/curl_example.php"; // Where you want to post data
    curl_setopt($ch, CURLOPT_URL,$url);
    curl_setopt($ch, CURLOPT_POST, true);  // Tell cURL you want to post something
    curl_setopt($ch, CURLOPT_POSTFIELDS, "var1=value1&var2=value2&var_n=value_n"); // Define what you want to post
    curl_setopt($ch, CURLOPT_RETURNTRANSFER, true); // Return the output in string format
    $output = curl_exec ($ch); // Execute

    curl_close ($ch); // Close cURL handle

    var_dump($output); // Show output
?>

Example found here: http://devzone.co.in/post-data-using-curl-in-php-a-simple-example/

Instead of using curl_setopt you can use curl_setopt_array.

http://php.net/manual/en/function.curl-setopt-array.php

PHP equivalent of .NET/Java's toString()

Double quotes should work too... it should create a string, then it should APPEND/INSERT the casted STRING value of $myVar in between 2 empty strings.

Regular cast vs. static_cast vs. dynamic_cast

Avoid using C-Style casts.

C-style casts are a mix of const and reinterpret cast, and it's difficult to find-and-replace in your code. A C++ application programmer should avoid C-style cast.

SQL Group By with an Order By

I don't know about MySQL, but in MS SQL, you can use the column index in the order by clause. I've done this before when doing counts with group bys as it tends to be easier to work with.

So

SELECT COUNT(id), `Tag` from `images-tags`
GROUP BY `Tag`
ORDER BY COUNT(id) DESC
LIMIT 20

Becomes

SELECT COUNT(id), `Tag` from `images-tags`
GROUP BY `Tag`
ORDER 1 DESC
LIMIT 20

Calculate distance between two latitude-longitude points? (Haversine formula)

I made a custom function in R to calculate haversine distance(km) between two spatial points using functions available in R base package.

custom_hav_dist <- function(lat1, lon1, lat2, lon2) {
R <- 6371
Radian_factor <- 0.0174533
lat_1 <- (90-lat1)*Radian_factor
lat_2 <- (90-lat2)*Radian_factor
diff_long <-(lon1-lon2)*Radian_factor

distance_in_km <- 6371*acos((cos(lat_1)*cos(lat_2))+ 
                 (sin(lat_1)*sin(lat_2)*cos(diff_long)))
rm(lat1, lon1, lat2, lon2)
return(distance_in_km)
}

Sample output

custom_hav_dist(50.31,19.08,54.14,19.39)
[1] 426.3987

PS: To calculate distances in miles, substitute R in function (6371) with 3958.756 (and for nautical miles, use 3440.065).

What's the difference between a temp table and table variable in SQL Server?

Another difference:

A table var can only be accessed from statements within the procedure that creates it, not from other procedures called by that procedure or nested dynamic SQL (via exec or sp_executesql).

A temp table's scope, on the other hand, includes code in called procedures and nested dynamic SQL.

If the table created by your procedure must be accessible from other called procedures or dynamic SQL, you must use a temp table. This can be very handy in complex situations.

How can I discover the "path" of an embedded resource?

I'm guessing that your class is in a different namespace. The canonical way to solve this would be to use the resources class and a strongly typed resource:

ProjectNamespace.Properties.Resources.file

Use the IDE's resource manager to add resources.

Getting parts of a URL (Regex)

Try the following:

^((ht|f)tp(s?)\:\/\/|~/|/)?([\w]+:\w+@)?([a-zA-Z]{1}([\w\-]+\.)+([\w]{2,5}))(:[\d]{1,5})?((/?\w+/)+|/?)(\w+\.[\w]{3,4})?((\?\w+=\w+)?(&\w+=\w+)*)?

It supports HTTP / FTP, subdomains, folders, files etc.

I found it from a quick google search:

http://geekswithblogs.net/casualjim/archive/2005/12/01/61722.aspx

How can I add (simple) tracing in C#?

DotNetCoders has a starter article on it: http://www.dotnetcoders.com/web/Articles/ShowArticle.aspx?article=50. They talk about how to set up the switches in the configuration file and how to write the code, but it is pretty old (2002).

There's another article on CodeProject: A Treatise on Using Debug and Trace classes, including Exception Handling, but it's the same age.

CodeGuru has another article on custom TraceListeners: Implementing a Custom TraceListener

What issues should be considered when overriding equals and hashCode in Java?

There are a couple of ways to do your check for class equality before checking member equality, and I think both are useful in the right circumstances.

  1. Use the instanceof operator.
  2. Use this.getClass().equals(that.getClass()).

I use #1 in a final equals implementation, or when implementing an interface that prescribes an algorithm for equals (like the java.util collection interfaces—the right way to check with with (obj instanceof Set) or whatever interface you're implementing). It's generally a bad choice when equals can be overridden because that breaks the symmetry property.

Option #2 allows the class to be safely extended without overriding equals or breaking symmetry.

If your class is also Comparable, the equals and compareTo methods should be consistent too. Here's a template for the equals method in a Comparable class:

final class MyClass implements Comparable<MyClass>
{

  …

  @Override
  public boolean equals(Object obj)
  {
    /* If compareTo and equals aren't final, we should check with getClass instead. */
    if (!(obj instanceof MyClass)) 
      return false;
    return compareTo((MyClass) obj) == 0;
  }

}

Detecting an undefined object property

I use if (this.variable) to test if it is defined. A simple if (variable), recommended in a previous answer, fails for me.

It turns out that it works only when a variable is a field of some object, obj.someField to check if it is defined in the dictionary. But we can use this or window as the dictionary object since any variable is a field in the current window, as I understand it. Therefore here is a test:

_x000D_
_x000D_
if (this.abc) 
    alert("defined"); 
else 
    alert("undefined");

abc = "abc";
if (this.abc) 
    alert("defined"); 
else 
    alert("undefined");
_x000D_
_x000D_
_x000D_

It first detects that variable abc is undefined and it is defined after initialization.

How to convert std::string to LPCWSTR in C++ (Unicode)

LPCWSTR lpcwName=std::wstring(strname.begin(), strname.end()).c_str()

Comparing Arrays of Objects in JavaScript

EDIT: You cannot overload operators in current, common browser-based implementations of JavaScript interpreters.

To answer the original question, one way you could do this, and mind you, this is a bit of a hack, simply serialize the two arrays to JSON and then compare the two JSON strings. That would simply tell you if the arrays are different, obviously you could do this to each of the objects within the arrays as well to see which ones were different.

Another option is to use a library which has some nice facilities for comparing objects - I use and recommend MochiKit.


EDIT: The answer kamens gave deserves consideration as well, since a single function to compare two given objects would be much smaller than any library to do what I suggest (although my suggestion would certainly work well enough).

Here is a naïve implemenation that may do just enough for you - be aware that there are potential problems with this implementation:

function objectsAreSame(x, y) {
   var objectsAreSame = true;
   for(var propertyName in x) {
      if(x[propertyName] !== y[propertyName]) {
         objectsAreSame = false;
         break;
      }
   }
   return objectsAreSame;
}

The assumption is that both objects have the same exact list of properties.

Oh, and it is probably obvious that, for better or worse, I belong to the only-one-return-point camp. :)

How do I REALLY reset the Visual Studio window layout?

How about running the following from command line,

Devenv.exe /ResetSettings

You could also save those settings in to a file, like so,

Devenv.exe /ResetSettings "C:\My Files\MySettings.vssettings"

The /ResetSettings switch, Restores Visual Studio default settings. Optionally resets the settings to the specified .vssettings file.

MSDN link

Getting all types that implement an interface

There are many valid answers already but I'd like to add anther implementation as a Type extension and a list of unit tests to demonstrate different scenarios:

public static class TypeExtensions
{
    public static IEnumerable<Type> GetAllTypes(this Type type)
    {
        var typeInfo = type.GetTypeInfo();
        var allTypes = GetAllImplementedTypes(type).Concat(typeInfo.ImplementedInterfaces);
        return allTypes;
    }

    private static IEnumerable<Type> GetAllImplementedTypes(Type type)
    {
        yield return type;
        var typeInfo = type.GetTypeInfo();
        var baseType = typeInfo.BaseType;
        if (baseType != null)
        {
            foreach (var foundType in GetAllImplementedTypes(baseType))
            {
                yield return foundType;
            }
        }
    }
}

This algorithm supports the following scenarios:

public static class GetAllTypesTests
{
    public class Given_A_Sample_Standalone_Class_Type_When_Getting_All_Types
        : Given_When_Then_Test
    {
        private Type _sut;
        private IEnumerable<Type> _expectedTypes;
        private IEnumerable<Type> _result;

        protected override void Given()
        {
            _sut = typeof(SampleStandalone);

            _expectedTypes =
                new List<Type>
                {
                    typeof(SampleStandalone),
                    typeof(object)
                };
        }

        protected override void When()
        {
            _result = _sut.GetAllTypes();
        }

        [Fact]
        public void Then_It_Should_Return_The_Right_Type()
        {
            _result.Should().BeEquivalentTo(_expectedTypes);
        }
    }

    public class Given_A_Sample_Abstract_Base_Class_Type_When_Getting_All_Types
        : Given_When_Then_Test
    {
        private Type _sut;
        private IEnumerable<Type> _expectedTypes;
        private IEnumerable<Type> _result;

        protected override void Given()
        {
            _sut = typeof(SampleBase);

            _expectedTypes =
                new List<Type>
                {
                    typeof(SampleBase),
                    typeof(object)
                };
        }

        protected override void When()
        {
            _result = _sut.GetAllTypes();
        }

        [Fact]
        public void Then_It_Should_Return_The_Right_Type()
        {
            _result.Should().BeEquivalentTo(_expectedTypes);
        }
    }

    public class Given_A_Sample_Child_Class_Type_When_Getting_All_Types
        : Given_When_Then_Test
    {
        private Type _sut;
        private IEnumerable<Type> _expectedTypes;
        private IEnumerable<Type> _result;

        protected override void Given()
        {
            _sut = typeof(SampleChild);

            _expectedTypes =
                new List<Type>
                {
                    typeof(SampleChild),
                    typeof(SampleBase),
                    typeof(object)
                };
        }

        protected override void When()
        {
            _result = _sut.GetAllTypes();
        }

        [Fact]
        public void Then_It_Should_Return_The_Right_Type()
        {
            _result.Should().BeEquivalentTo(_expectedTypes);
        }
    }

    public class Given_A_Sample_Base_Interface_Type_When_Getting_All_Types
        : Given_When_Then_Test
    {
        private Type _sut;
        private IEnumerable<Type> _expectedTypes;
        private IEnumerable<Type> _result;

        protected override void Given()
        {
            _sut = typeof(ISampleBase);

            _expectedTypes =
                new List<Type>
                {
                    typeof(ISampleBase)
                };
        }

        protected override void When()
        {
            _result = _sut.GetAllTypes();
        }

        [Fact]
        public void Then_It_Should_Return_The_Right_Type()
        {
            _result.Should().BeEquivalentTo(_expectedTypes);
        }
    }

    public class Given_A_Sample_Child_Interface_Type_When_Getting_All_Types
        : Given_When_Then_Test
    {
        private Type _sut;
        private IEnumerable<Type> _expectedTypes;
        private IEnumerable<Type> _result;

        protected override void Given()
        {
            _sut = typeof(ISampleChild);

            _expectedTypes =
                new List<Type>
                {
                    typeof(ISampleBase),
                    typeof(ISampleChild)
                };
        }

        protected override void When()
        {
            _result = _sut.GetAllTypes();
        }

        [Fact]
        public void Then_It_Should_Return_The_Right_Type()
        {
            _result.Should().BeEquivalentTo(_expectedTypes);
        }
    }

    public class Given_A_Sample_Implementation_Class_Type_When_Getting_All_Types
        : Given_When_Then_Test
    {
        private Type _sut;
        private IEnumerable<Type> _expectedTypes;
        private IEnumerable<Type> _result;

        protected override void Given()
        {
            _sut = typeof(SampleImplementation);

            _expectedTypes =
                new List<Type>
                {
                    typeof(SampleImplementation),
                    typeof(SampleChild),
                    typeof(SampleBase),
                    typeof(ISampleChild),
                    typeof(ISampleBase),
                    typeof(object)
                };
        }

        protected override void When()
        {
            _result = _sut.GetAllTypes();
        }

        [Fact]
        public void Then_It_Should_Return_The_Right_Type()
        {
            _result.Should().BeEquivalentTo(_expectedTypes);
        }
    }

    public class Given_A_Sample_Interface_Instance_Type_When_Getting_All_Types
        : Given_When_Then_Test
    {
        private Type _sut;
        private IEnumerable<Type> _expectedTypes;
        private IEnumerable<Type> _result;

        class Foo : ISampleChild { }

        protected override void Given()
        {
            var foo = new Foo();
            _sut = foo.GetType();

            _expectedTypes =
                new List<Type>
                {
                    typeof(Foo),
                    typeof(ISampleChild),
                    typeof(ISampleBase),
                    typeof(object)
                };
        }

        protected override void When()
        {
            _result = _sut.GetAllTypes();
        }

        [Fact]
        public void Then_It_Should_Return_The_Right_Type()
        {
            _result.Should().BeEquivalentTo(_expectedTypes);
        }
    }

    sealed class SampleStandalone { }
    abstract class SampleBase { }
    class SampleChild : SampleBase { }
    interface ISampleBase { }
    interface ISampleChild : ISampleBase { }
    class SampleImplementation : SampleChild, ISampleChild { }
}

What is MVC and what are the advantages of it?

I think another benefit of using the MVC pattern is that it opens up the doors to other approaches to the design, such as MVP/Presenter first and the many other MV* patterns.

Without this fundamental segregation of the design "components" the adoption of these techniques would be much more difficult.

I think it helps to make your code even more interface-based.. Not only within the individual project, but you can almost start to develop common "views" which mean you can template lot more of the "grunt" code used in your applications. For example, a very abstract "data view" which simply takes a bunch of data and throws it to a common grid layout.

Edit:

If I remember correctly, this is a pretty good podcast on MV* patterns (listened to it a while ago!)

How to set encoding in .getJSON jQuery

I think that you'll probably have to use $.ajax() if you want to change the encoding, see the contentType param below (the success and error callbacks assume you have <div id="success"></div> and <div id="error"></div> in the html):

$.ajax({
    type: "POST",
    url: "SomePage.aspx/GetSomeObjects",
    contentType: "application/json; charset=utf-8",
    dataType: "json",
    data: "{id: '" + someId + "'}",
    success: function(json) {
        $("#success").html("json.length=" + json.length);
        itemAddCallback(json);
    },
    error: function (xhr, textStatus, errorThrown) {
        $("#error").html(xhr.responseText);
    }
});

I actually just had to do this about an hour ago, what a coincidence!

How can I pass arguments to a batch file?

Let's keep this simple.

Here is the .cmd file.

@echo off
rem this file is named echo_3params.cmd
echo %1
echo %2
echo %3
set v1=%1
set v2=%2
set v3=%3
echo v1 equals %v1%
echo v2 equals %v2%
echo v3 equals %v3%

Here are 3 calls from the command line.

C:\Users\joeco>echo_3params 1abc 2 def  3 ghi
1abc
2
def
v1 equals 1abc
v2 equals 2
v3 equals def

C:\Users\joeco>echo_3params 1abc "2 def"  "3 ghi"
1abc
"2 def"
"3 ghi"
v1 equals 1abc
v2 equals "2 def"
v3 equals "3 ghi"

C:\Users\joeco>echo_3params 1abc '2 def'  "3 ghi"
1abc
'2
def'
v1 equals 1abc
v2 equals '2
v3 equals def'

C:\Users\joeco>

How can I play sound in Java?

There is an alternative to importing the sound files which works in both applets and applications: convert the audio files into .java files and simply use them in your code.

I have developed a tool which makes this process a lot easier. It simplifies the Java Sound API quite a bit.

http://stephengware.com/projects/soundtoclass/

Filtering collections in C#

To do it in place, you can use the RemoveAll method of the "List<>" class along with a custom "Predicate" class...but all that does is clean up the code... under the hood it's doing the same thing you are...but yes, it does it in place, so you do same the temp list.

How can I measure the similarity between two images?

There's software for content-based image retrieval, which does (partially) what you need. All references and explanations are linked from the project site and there's also a short text book (Kindle): LIRE

Insert into ... values ( SELECT ... FROM ... )

Both the answers I see work fine in Informix specifically, and are basically standard SQL. That is, the notation:

INSERT INTO target_table[(<column-list>)] SELECT ... FROM ...;

works fine with Informix and, I would expect, all the DBMS. (Once upon 5 or more years ago, this is the sort of thing that MySQL did not always support; it now has decent support for this sort of standard SQL syntax and, AFAIK, it would work OK on this notation.) The column list is optional but indicates the target columns in sequence, so the first column of the result of the SELECT will go into the first listed column, etc. In the absence of the column list, the first column of the result of the SELECT goes into the first column of the target table.

What can be different between systems is the notation used to identify tables in different databases - the standard has nothing to say about inter-database (let alone inter-DBMS) operations. With Informix, you can use the following notation to identify a table:

[dbase[@server]:][owner.]table

That is, you may specify a database, optionally identifying the server that hosts that database if it is not in the current server, followed by an optional owner, dot, and finally the actual table name. The SQL standard uses the term schema for what Informix calls the owner. Thus, in Informix, any of the following notations could identify a table:

table
"owner".table
dbase:table
dbase:owner.table
dbase@server:table
dbase@server:owner.table

The owner in general does not need to be quoted; however, if you do use quotes, you need to get the owner name spelled correctly - it becomes case-sensitive. That is:

someone.table
"someone".table
SOMEONE.table

all identify the same table. With Informix, there's a mild complication with MODE ANSI databases, where owner names are generally converted to upper-case (informix is the exception). That is, in a MODE ANSI database (not commonly used), you could write:

CREATE TABLE someone.table ( ... )

and the owner name in the system catalog would be "SOMEONE", rather than 'someone'. If you enclose the owner name in double quotes, it acts like a delimited identifier. With standard SQL, delimited identifiers can be used many places. With Informix, you can use them only around owner names -- in other contexts, Informix treats both single-quoted and double-quoted strings as strings, rather than separating single-quoted strings as strings and double-quoted strings as delimited identifiers. (Of course, just for completeness, there is an environment variable, DELIMIDENT, that can be set - to any value, but Y is safest - to indicate that double quotes always surround delimited identifiers and single quotes always surround strings.)

Note that MS SQL Server manages to use [delimited identifiers] enclosed in square brackets. It looks weird to me, and is certainly not part of the SQL standard.

Best programming based games

Another good one is CEEBot. It teaches C / Java style programming in a fun, robot-programming kind of game. It is aimed at 10-15 year olds, but it is a good one.

Copy/duplicate database without using mysqldump

In PHP:

function cloneDatabase($dbName, $newDbName){
    global $admin;
    $db_check = @mysql_select_db ( $dbName );
    $getTables  =   $admin->query("SHOW TABLES");   
    $tables =   array();
    while($row = mysql_fetch_row($getTables)){
        $tables[]   =   $row[0];
    }
    $createTable    =   mysql_query("CREATE DATABASE `$newDbName` DEFAULT CHARACTER SET utf8 COLLATE utf8_general_ci;") or die(mysql_error());
    foreach($tables as $cTable){
        $db_check   =   @mysql_select_db ( $newDbName );
        $create     =   $admin->query("CREATE TABLE $cTable LIKE ".$dbName.".".$cTable);
        if(!$create) {
            $error  =   true;
        }
        $insert     =   $admin->query("INSERT INTO $cTable SELECT * FROM ".$dbName.".".$cTable);
    }
    return !isset($error);
}


// usage
$clone  = cloneDatabase('dbname','newdbname');  // first: toCopy, second: new database

Delete all but the most recent X files in bash

ls -tQ | tail -n+4 | xargs rm

List filenames by modification time, quoting each filename. Exclude first 3 (3 most recent). Remove remaining.

EDIT after helpful comment from mklement0 (thanks!): corrected -n+3 argument, and note this will not work as expected if filenames contain newlines and/or the directory contains subdirectories.

What is the best free memory leak detector for a C/C++ program and its plug-in DLLs?

Try Jochen Kalmbach's Memory Leak Detector on Code Project. The URL to the latest version was somewhere in the comments when I last checked.

Python module for converting PDF to text

The PDFMiner package has changed since codeape posted.

EDIT (again):

PDFMiner has been updated again in version 20100213

You can check the version you have installed with the following:

>>> import pdfminer
>>> pdfminer.__version__
'20100213'

Here's the updated version (with comments on what I changed/added):

def pdf_to_csv(filename):
    from cStringIO import StringIO  #<-- added so you can copy/paste this to try it
    from pdfminer.converter import LTTextItem, TextConverter
    from pdfminer.pdfparser import PDFDocument, PDFParser
    from pdfminer.pdfinterp import PDFResourceManager, PDFPageInterpreter

    class CsvConverter(TextConverter):
        def __init__(self, *args, **kwargs):
            TextConverter.__init__(self, *args, **kwargs)

        def end_page(self, i):
            from collections import defaultdict
            lines = defaultdict(lambda : {})
            for child in self.cur_item.objs:
                if isinstance(child, LTTextItem):
                    (_,_,x,y) = child.bbox                   #<-- changed
                    line = lines[int(-y)]
                    line[x] = child.text.encode(self.codec)  #<-- changed

            for y in sorted(lines.keys()):
                line = lines[y]
                self.outfp.write(";".join(line[x] for x in sorted(line.keys())))
                self.outfp.write("\n")

    # ... the following part of the code is a remix of the 
    # convert() function in the pdfminer/tools/pdf2text module
    rsrc = PDFResourceManager()
    outfp = StringIO()
    device = CsvConverter(rsrc, outfp, codec="utf-8")  #<-- changed 
        # becuase my test documents are utf-8 (note: utf-8 is the default codec)

    doc = PDFDocument()
    fp = open(filename, 'rb')
    parser = PDFParser(fp)       #<-- changed
    parser.set_document(doc)     #<-- added
    doc.set_parser(parser)       #<-- added
    doc.initialize('')

    interpreter = PDFPageInterpreter(rsrc, device)

    for i, page in enumerate(doc.get_pages()):
        outfp.write("START PAGE %d\n" % i)
        interpreter.process_page(page)
        outfp.write("END PAGE %d\n" % i)

    device.close()
    fp.close()

    return outfp.getvalue()

Edit (yet again):

Here is an update for the latest version in pypi, 20100619p1. In short I replaced LTTextItem with LTChar and passed an instance of LAParams to the CsvConverter constructor.

def pdf_to_csv(filename):
    from cStringIO import StringIO  
    from pdfminer.converter import LTChar, TextConverter    #<-- changed
    from pdfminer.layout import LAParams
    from pdfminer.pdfparser import PDFDocument, PDFParser
    from pdfminer.pdfinterp import PDFResourceManager, PDFPageInterpreter

    class CsvConverter(TextConverter):
        def __init__(self, *args, **kwargs):
            TextConverter.__init__(self, *args, **kwargs)

        def end_page(self, i):
            from collections import defaultdict
            lines = defaultdict(lambda : {})
            for child in self.cur_item.objs:
                if isinstance(child, LTChar):               #<-- changed
                    (_,_,x,y) = child.bbox                   
                    line = lines[int(-y)]
                    line[x] = child.text.encode(self.codec)

            for y in sorted(lines.keys()):
                line = lines[y]
                self.outfp.write(";".join(line[x] for x in sorted(line.keys())))
                self.outfp.write("\n")

    # ... the following part of the code is a remix of the 
    # convert() function in the pdfminer/tools/pdf2text module
    rsrc = PDFResourceManager()
    outfp = StringIO()
    device = CsvConverter(rsrc, outfp, codec="utf-8", laparams=LAParams())  #<-- changed
        # becuase my test documents are utf-8 (note: utf-8 is the default codec)

    doc = PDFDocument()
    fp = open(filename, 'rb')
    parser = PDFParser(fp)       
    parser.set_document(doc)     
    doc.set_parser(parser)       
    doc.initialize('')

    interpreter = PDFPageInterpreter(rsrc, device)

    for i, page in enumerate(doc.get_pages()):
        outfp.write("START PAGE %d\n" % i)
        if page is not None:
            interpreter.process_page(page)
        outfp.write("END PAGE %d\n" % i)

    device.close()
    fp.close()

    return outfp.getvalue()

EDIT (one more time):

Updated for version 20110515 (thanks to Oeufcoque Penteano!):

def pdf_to_csv(filename):
    from cStringIO import StringIO  
    from pdfminer.converter import LTChar, TextConverter
    from pdfminer.layout import LAParams
    from pdfminer.pdfparser import PDFDocument, PDFParser
    from pdfminer.pdfinterp import PDFResourceManager, PDFPageInterpreter

    class CsvConverter(TextConverter):
        def __init__(self, *args, **kwargs):
            TextConverter.__init__(self, *args, **kwargs)

        def end_page(self, i):
            from collections import defaultdict
            lines = defaultdict(lambda : {})
            for child in self.cur_item._objs:                #<-- changed
                if isinstance(child, LTChar):
                    (_,_,x,y) = child.bbox                   
                    line = lines[int(-y)]
                    line[x] = child._text.encode(self.codec) #<-- changed

            for y in sorted(lines.keys()):
                line = lines[y]
                self.outfp.write(";".join(line[x] for x in sorted(line.keys())))
                self.outfp.write("\n")

    # ... the following part of the code is a remix of the 
    # convert() function in the pdfminer/tools/pdf2text module
    rsrc = PDFResourceManager()
    outfp = StringIO()
    device = CsvConverter(rsrc, outfp, codec="utf-8", laparams=LAParams())
        # becuase my test documents are utf-8 (note: utf-8 is the default codec)

    doc = PDFDocument()
    fp = open(filename, 'rb')
    parser = PDFParser(fp)       
    parser.set_document(doc)     
    doc.set_parser(parser)       
    doc.initialize('')

    interpreter = PDFPageInterpreter(rsrc, device)

    for i, page in enumerate(doc.get_pages()):
        outfp.write("START PAGE %d\n" % i)
        if page is not None:
            interpreter.process_page(page)
        outfp.write("END PAGE %d\n" % i)

    device.close()
    fp.close()

    return outfp.getvalue()

Get OS-level system information

Hey you can do this with java/com integration. By accessing WMI features you can get all the information.

How do I get the full url of the page I am on in C#

Better to use Request.Url.OriginalString than Request.Url.ToString() (according to MSDN)

Is Java "pass-by-reference" or "pass-by-value"?

A reference is always a value when represented, no matter what language you use.

Getting an outside of the box view, let's look at Assembly or some low level memory management. At the CPU level a reference to anything immediately becomes a value if it gets written to memory or to one of the CPU registers. (That is why pointer is a good definition. It is a value, which has a purpose at the same time).

Data in memory has a Location and at that location there is a value (byte,word, whatever). In Assembly we have a convenient solution to give a Name to certain Location (aka variable), but when compiling the code, the assembler simply replaces Name with the designated location just like your browser replaces domain names with IP addresses.

Down to the core it is technically impossible to pass a reference to anything in any language without representing it (when it immediately becomes a value).

Lets say we have a variable Foo, its Location is at the 47th byte in memory and its Value is 5. We have another variable Ref2Foo which is at 223rd byte in memory, and its value will be 47. This Ref2Foo might be a technical variable, not explicitly created by the program. If you just look at 5 and 47 without any other information, you will see just two Values. If you use them as references then to reach to 5 we have to travel:

(Name)[Location] -> [Value at the Location]
---------------------
(Ref2Foo)[223]  -> 47
(Foo)[47]       -> 5

This is how jump-tables work.

If we want to call a method/function/procedure with Foo's value, there are a few possible way to pass the variable to the method, depending on the language and its several method invocation modes:

  1. 5 gets copied to one of the CPU registers (ie. EAX).
  2. 5 gets PUSHd to the stack.
  3. 47 gets copied to one of the CPU registers
  4. 47 PUSHd to the stack.
  5. 223 gets copied to one of the CPU registers.
  6. 223 gets PUSHd to the stack.

In every cases above a value - a copy of an existing value - has been created, it is now upto the receiving method to handle it. When you write "Foo" inside the method, it is either read out from EAX, or automatically dereferenced, or double dereferenced, the process depends on how the language works and/or what the type of Foo dictates. This is hidden from the developer until she circumvents the dereferencing process. So a reference is a value when represented, because a reference is a value that has to be processed (at language level).

Now we have passed Foo to the method:

  • in case 1. and 2. if you change Foo (Foo = 9) it only affects local scope as you have a copy of the Value. From inside the method we cannot even determine where in memory the original Foo was located.
  • in case 3. and 4. if you use default language constructs and change Foo (Foo = 11), it could change Foo globally (depends on the language, ie. Java or like Pascal's procedure findMin(x, y, z: integer;var m: integer);). However if the language allows you to circumvent the dereference process, you can change 47, say to 49. At that point Foo seems to have been changed if you read it, because you have changed the local pointer to it. And if you were to modify this Foo inside the method (Foo = 12) you will probably FUBAR the execution of the program (aka. segfault) because you will write to a different memory than expected, you can even modify an area that is destined to hold executable program and writing to it will modify running code (Foo is now not at 47). BUT Foo's value of 47 did not change globally, only the one inside the method, because 47 was also a copy to the method.
  • in case 5. and 6. if you modify 223 inside the method it creates the same mayhem as in 3. or 4. (a pointer, pointing to a now bad value, that is again used as a pointer) but this is still a local problem, as 223 was copied. However if you are able to dereference Ref2Foo (that is 223), reach to and modify the pointed value 47, say, to 49, it will affect Foo globally, because in this case the methods got a copy of 223 but the referenced 47 exists only once, and changing that to 49 will lead every Ref2Foo double-dereferencing to a wrong value.

Nitpicking on insignificant details, even languages that do pass-by-reference will pass values to functions, but those functions know that they have to use it for dereferencing purposes. This pass-the-reference-as-value is just hidden from the programmer because it is practically useless and the terminology is only pass-by-reference.

Strict pass-by-value is also useless, it would mean that a 100 Mbyte array should have to be copied every time we call a method with the array as argument, therefore Java cannot be stricly pass-by-value. Every language would pass a reference to this huge array (as a value) and either employs copy-on-write mechanism if that array can be changed locally inside the method or allows the method (as Java does) to modify the array globally (from the caller's view) and a few languages allows to modify the Value of the reference itself.

So in short and in Java's own terminology, Java is pass-by-value where value can be: either a real value or a value that is a representation of a reference.

What are the differences between a HashMap and a Hashtable in Java?

HashMap is emulated and therefore usable in GWT client code whereas Hashtable is not.

What is the command to truncate a SQL Server log file?

if I remember well... in query analyzer or equivalent:

BACKUP LOG  databasename  WITH TRUNCATE_ONLY

DBCC SHRINKFILE (  databasename_Log, 1)

How to tell which disk Windows Used to Boot

There is no boot.ini on a machine with just Vista installed.

How do you want to identify the drive/partition: by the windows drive letter it is mapped to (eg. c:\, d:) or by how its hardware signature (which bus, etc).

For the simple case check out GetSystemDirectory

Force unmount of NFS-mounted directory

You might try a lazy unmount:

umount -l

How do you beta test an iphone app?

Note that there is a distinction between traditional "beta testing" which is done by professional QA engineers, and "public beta testing" which is releasing your product to the public before it's ready : )

You can do "beta testing" -- loading to specific iPhones/iPods your testers will be using. You can't do "public beta testing" -- pre-releasing to the public.

How to find a Java Memory Leak

Checkout this screen cast about finding memory leaks with JProfiler. It's visual explanation of @Dima Malenko Answer.

Note: Though JProfiler is not freeware, But Trial version can deal with current situation.