Porting PHP array data structure into Java

Question

I'm working with this data structure in PHP

Array
(
 [leigh@bla] => Array
 (
 [chat1] => Array
 (
 [0] => Array
 (
 [0] => 0
 [1] => hi
 [2] => 123213312
 )
 )
 [chat2] => Array
 (
 [0] => Array
 (
 [0] => 0
 [1] => whatever?
 [2] => 123213312
 )
 [1] => Array
 (
 [0] => 1
 [1] => ok
 [2] => 23123213
 )
 )
 )
 [nelson@bla] => Array
 (
 [chat1] => Array
 (
 [0] => Array
 (
 [0] => 1
 [1] => hello
 [2] => 1232132123
 )
 )
 )
)

Here is the PHP code:

<?php
$arrTemp['leigh@bla']['chat1'][] = array(0, 'hi', '123213312');
$arrTemp['leigh@bla']['chat2'][] = array(0, 'whatever?', '123213312');
$arrTemp['leigh@bla']['chat2'][] = array(1, 'ok', '23123213');
$arrTemp['nelson@bla'] = array('chat1'=>array(array(1, 'hello', '1232132123')));
echo '<pre>';
print_r($arrTemp);

I'm trying to store this structure in Java. But struggling to find a suitable type, i've tried ArrayList> etc. What would be the best way of storing this structure in Java?

• Luiggi Mendoza: Is this for a kind of experiment or real code?
• JB Nizet: Think in terms of objects. Not in terms of data structures. What does this PHP data structure represent?
• Andy Davies: I'm looking at porting some PHP code into Java, the PHP code in this question just mocks up what is actually created for simplicity. It represents chat data for Microsoft OCS server
• f1sh: The array directly underneath of the "leigh" part starts with the index 1 instead of 0 - ist that important?
• Andy Davies: I've updated the PHP and debug output to make it more obvious about the 2nd key. Leigh could contain many chats which contain the inner structure of flag, message, timestamp

Answer 1

The outer structure seems to be an associative array (the key is "leigh"), so for that level you need a (Hash)Map (there are no associative arrays in java, a Map is the equivalent).

Inside of that seems to be a list of lists and inside of that some structure that holds 3 atomic values (let's call them a, b and c) that look like Integer, String, Integer.

A simple container for those 3 values would look like this:

class InnerStructure {
 Integer a, c;
 String b;
}

and to represent your structure:

Map<String, List<List<InnerStructure>>> wholeStructure;

Note that Map and List are only interfaces, implementations for those are HashMap and LinkedList or ArrayList.

Imitating your php code to fill this structure:

Map<String, List<List<InnerStructure>>> wholeStructure = new HashMap<String, List<List<InnerStructure>>>();
List<List<InnerStructure>> outerList = new ArrayList<List<InnerStructure>>();
List<InnerStructure> innerList = new ArrayList<InnerStructure>();
InnerStructure innerData = new InnerStructure();
innerData.a = 1;
innerData.b = "hello";
innerData.c = 1232132123;
innerList.add(innerData);
outerList.add(innerList);
wholeStructure.put("leigh", outerList);

Of course i strongly recommend that you don't simply work with nameless lists, but instead find names or terms that describe the acutal use for this hierarchy. Then you create classes for those and aggregate the lists into these classes, which makes it way more readable, typesafe and less painful to inspect.

• Andy Davies: Thanks there is another key [leigh] => Array ([1] the value 1 is a numeric key other than that they are just lists. Leigh => numeric key => List <InnerStructure> I think
• f1sh: There is another entry in the php's top level array with the key of "leigh"? That doesn't work, not even in php.