Variable length (Dynamic) Arrays in Java

Question

I was wondering how to initialise an integer array such that it's size and values change through out the execution of my program, any suggestions?

Answer 1

Yes: use ArrayList.

In Java, "normal" arrays are fixed-size. You have to give them a size and can't expand them or contract them; to change the size, you have to make a new array and copy the data you want, which is inefficient and a pain for you.

Fortunately, there are all kinds of built-in classes that implement common data structures, and other useful tools too. You'll want to check the Java 6 API for a full list of them.

One caveat: ArrayList can only hold objects (e.g. Integers), not primitives (e.g. ints). In MOST cases, autoboxing/autounboxing will take care of this for you silently, but you could get some weird behavior depending on what you're doing.

Answer 2

You can't change the size of an array. You can, however, create a new array with the right size and copy the data from the old array to the new.

But your best option is to use IntList from jacarta commons. (http://commons.apache.org/primitives/api-release/org/apache/commons/collections/primitives/IntList.html)

It works just like a List but takes less space and is more efficient than that, because it stores int's instead of storing wrapper objects over int's (that's what the Integer class is).

Answer 3

How about using a List instead? For example, ArrayList<integer>

Answer 4

Arrays are fixed size once instantiated. You can use a List instead.

Autoboxing make a List usable similar to an array, you can put simply int-values into it:

List<Integer> list = new ArrayList<Integer>();
list.add(1);
list.add(2);
list.add(3);

Answer 5

Arrays in Java are of fixed size. What you'd need is an ArrayList, one of a number of extremely valuable Collections available in Java.

Instead of

Integer[] ints = new Integer[x]

you use

List<Integer> ints = new ArrayList<Integer>

Then to change the list you use ints.add(y) and ints.remove(z) amongst many other handy methods you can find in the appropriate Javadocs.

I strongly recommend studying the Collections classes available in Java as they are very powerful and give you a lot of builtin functionality that Java-newbies tend to try to rewrite themselves unnecessarily.