Array resizing

[Ben Hodgson]

How do you dynamically resize an array? I'd like to declare it with an initial size, but add to its size if I go out of bounds.
So I'd start with:
String sStuff[] = new String[100];
to get the initial size - is there a way to up the size by, say, 10 elements a time if I need to?

[Art Metzer]

The short answer here, Ben, is "no". You cannot dynamically resize an array.
But why not look into <pre>java.util.Vector</pre> instead? Read all about it.
HTH
Art
[This message has been edited by Art Metzer (edited April 04, 2001).]

[Michael Waites]

You can write a method that will expand the array (by cheating) but it is clumsy and somewhat backwards when compared to Vector. But here ya go anywho:

public String[] increaseArray(String[] theArray, int increaseBy)
{
    int i = theArray.length;
    int n = ++i;
    String[] newArray = new String[n];
    for(int cnt=0;cnt<theArray.length;cnt++)>
    {
        newArray[cnt] = theArray[cnt];
    }
    return newArray;
}

Good luck!!
Michael

[Ben Hodgson]

Excellent - I liked both of those. I'm happy using Vectors, so I'll probably stick with them. Good to find out about the array thing (and the work around), so thanks for the answers, very much appreciated.

[octavyn pittman]

Remember, however, that arrays typically perform better than Vectors, if that is a consideration later on.
And, as Peter Haggar points out in his book Practical Java, there is a System class in the java.lang package with a method called
arraycopy(Obj src, int src_pos, Obj dest, int dest_pos, int length);
It takes a sorce array and a destination array, and using starting positions and a length, to quickly copy an array (nearly twice as fast as a for loop).
The code would look like this:

public void copyPlusSizeArray(int[] source, int[] destination) {
    int size = source.length;
    System.arraycopy( source, 0, destination, 0, size);
}

Apparently this is faster because the method is implemented as a native method, which can more directly and efficiently transfer the contents in memory from source to destination.
However, the arraycopy method has a number of gotchas to watch out for if you look in the API when you go beyond simple copying like above.
OP