Java associative-array

Question

How can I create and fetch associative arrays in Java like I can in PHP   For example    arr 0   name      demo    arr 0   fname      fdemo    arr 1   name      test    arr 1   fname      fname

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You can accomplish this via Maps  Something like   Map lt String  String gt    arr   new HashMap lt String  String gt  2     arr 0  put  name    demo      But as you start using Java I am sure you will find that if you create a class model that represents your data will be your best options  I would do  class Person  String name  String fname    List lt Person gt  people   new ArrayList lt Person gt     Person p   new Person    p name    demo   p fname    fdemo   people add p

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Regarding the PHP comment  No  PHP wouldn t like it   Actually  PHP would keep on chugging unless you set some very restrictive  for PHP  exception error levels   and maybe not even then    What WILL happen by default is that an access to a non existing variable out of bounds array element  unsets  your value that you re assigning to  NO  that is NOT null  PHP has a Perl C lineage  from what I understand  So there are  unset and non existing variables  values which ARE set but are NULL  Boolean False values  then everything else that standard langauges have  You have to test for those separately  OR choose the RIGHT evaluation built in function syntax

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Java equivalent of Perl  39 s hash  HashMap lt Integer  HashMap lt String  String gt  gt  hash

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Java doesn t have associative arrays  the closest thing you can get is the Map interface  Here s a sample from that page   import java util     public class Freq       public static void main String   args            Map lt String  Integer gt  m   new HashMap lt String  Integer gt                 Initialize frequency table from command line         for  String a   args                Integer freq   m get a               m put a   freq    null    1   freq   1                      System out println m size       distinct words             System out println m             If run with    java Freq if it is to be it is up to me to delegate   You ll get   8 distinct words   to 3  delegate 1  be 1  it 2  up 1  if 1  me 1  is 2

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Java doesn t support associative arrays  however this could easily be achieved using a Map  E g     Map lt String  String gt  map   new HashMap lt String  String gt     map put  name    demo    map put  fname    fdemo       etc  map get  name       returns  demo    Even more accurate to your example  since you can replace String with any object that meet your needs  would be to declare    List lt Map lt String  String gt  gt  data   new ArrayList lt  gt     data add 0  map   data get 0  get  name       See the official documentation for more information

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Object     data       mykey1    myval1      mykey2    myval2     new Date    new Integer 1         Yes  this require iteration for searchting value by key  but if you need all of them  this will be the best choice

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Actually Java does support associative arrays they are called dictionaries

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Look at the Map interface  and at the concrete class HashMap   To create a Map   Map lt String  String gt  assoc   new HashMap lt String  String gt       To add a key-value pair   assoc put  name    demo      To retrieve the value associated with a key   assoc get  name     And sure  you may create an array of Maps  as it seems to be what you want   Map lt String  String gt    assoc

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Java doesn t have associative arrays like PHP does   There are various solutions for what you are doing  such as using a Map  but it depends on how you want to look up the information  You can easily write a class that holds all your information and store instances of them in an ArrayList   public class Foo      public String name  fname       public Foo String name  String fname           this name   name          this fname   fname            And then     List lt Foo gt  foos   new ArrayList lt Foo gt     foos add new Foo  demo   fdemo     foos add new Foo  test   fname       So you can access them like     foos get 0  name    gt   demo

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Associative arrays in Java like in PHP     SlotMap hmap   new SlotHashMap    String key    k01   String value    123456      Add key value hmap put  key  value        check if key exists key value if   hmap containsKey key                               loop over hmap Set mapkeys    hmap keySet    for   Iterator iterator   mapkeys iterator    iterator hasNext         String key    String  iterator next      String value   hmap get key       More info  see Class SoftHashMap   https   shiro apache org static 1 2 2 apidocs org apache shiro util SoftHashMap html

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Well i also was in search of Associative array and found the List of maps as the best solution   import java util ArrayList  import java util HashMap  import java util List  import java util Map    public class testHashes    public static void main String args         Map lt String String gt  myMap1   new HashMap lt String  String gt          List lt Map lt String   String gt  gt  myMap    new ArrayList lt Map lt String String gt  gt          myMap1 put  URL    Val0        myMap1 put  CRC    Vla1        myMap1 put  SIZE    Vla2        myMap1 put  PROGRESS    Vla2         myMap add 0 myMap1       myMap add 1 myMap1        for  Map lt String  String gt  map   myMap            System out println map get  URL                  System out println myMap

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There is no such thing as associative array in Java  Its closest relative is a Map  which is strongly typed  however has less elegant syntax API   This is the closest you can get based on your example   Map lt Integer  Map lt String  String gt  gt  arr        org apache commons collections map LazyMap decorate           new HashMap    new InstantiateFactory HashMap class        arr 0   name      demo   arr get 0  put  name    demo     System out println arr get 0  get  name     System out println arr get 1  get  name          yields null

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Use ArrayList  lt  Map  lt   String  String      Here a code sample    ArrayList lt Map lt String  String gt  gt  products   new ArrayList lt Map lt String  String gt  gt     while  iterator hasNext               Map lt String  String gt  product   new HashMap lt String  String gt              Element currentProduct   iterator next             product put  id  currentProduct get  id              product put  name    currentProduct get  name               products add product      System out println  products       products     Output    products     id 0001  name prod1    id 0002  name prod2

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Thinking more about it  I would like to throw out tuples as a more general-purpose way of dealing with this problem   While tuples are not native to Java  I use Javatuples to provide me the same functionality which would exist in other languages   An example of how to deal with the question asked is  Map lt Pair lt Integer  String gt   String gt  arr   new HashMap lt Pair lt Integer  String gt   String gt     Pair p1   new Pair 0   name    arr put p1   demo      I like this approach because it can be extended to triples and other higher ordered groupings with api provided classes and methods

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In JDK 1 5  http   tinyurl com 3m2lxju  there is even a note   NOTE  This class is obsolete  New implementations should implement the Map interface  rather than extending this class   Regards  N

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