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2008-11-03T10:43:37Z

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== When to use Arrays and Lists ==

Someone has suggested using arrays to represent the Transactions and suggested the following code.
private Transaction[] transactionHistory;
private int numberOfTransactions;

transactionHistory[ numberOfTransactions++ ] = new Transaction( ... );

There is one (''big'') problem with that - arrays are of fixed size. Once you initialize an array (giving its size or putting items into it) you '''cannot change the size of that array object'''. You can fake a dynamically expanding array using
System.arrayCopy(...)
method. But its very tedious and not a very efficient way of doing it. (e.g. you'll have to keep checking that the array is not yet full each time you are adding a Transaction object)

<code>List</code> (and any java.utils.Collection class) already takes care of this for you - so why try to re-invent the wheel?

Remember these two simple guidelines when deciding what data structure to use to represent a group of objects:
:* Use arrays (fixed size) if your collection's size is not going to change
:* Use a List (e.g. ArrayList, Vector etc) if your collection will change in size (or you don't know its size when you are initializing the instance).

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