Bug in java arrays?

Question

Hi, just found this in a toy program and thought it might be a bug in the way java handles arrays... I'm working on Suse 8.0 & jdk 1.4, Red Hat 7.x/8.x with jdk 1.4 and Solaris 4 jdk 1.4:
If you have a method like this:
    public static void resize(int[] arr, int size) {
        int[] tmp = arr;
        int iterate;
        arr = new int[size];  // disassociate tmp from arr
        iterate = size > tmp.length ? tmp.length : size;
        for(int x = 0; x < iterate; x++) {
            arr[x] = tmp[x];
    }and try to call it from another class like this:
        /* could this possibly be a bug in java??? */
        Arrays.resize(state, state.length + 1);  // make array bigger
        state[state.length - 1] = start;  // store current room in arrayI get an ArrayIndexOutOfBoundsException on the call to assign start to the last index of state, which means that the new array knows its new length, but can't assign to it.
The solution to my problem was to return arr in the resize() method and assign the returned value to state.
This seems to go against what its supposed to happen (that the array is rezized and the pointer just updated)
Is this a bug in java or is it te desired behaviour?
dave.

Answer 1

But when I create the 'new' array I'm assigning the
pointer to the place where the previous array pointer
was... This should be completely legal. Yes, it's completely legal, but it doesn't do what you want :)
The variable in method to which you assign a new and longer array is a different one than the pointer you have in another method.
If you just call a function to assign values to an
array like this:> public void update(int[]arr){
arr[0] = 2;
} > and then use some code to look at the array you
passed: > int[]x = {1,2,3,4};
update(x);
system.out.println(x[0]);> you would expect to get 2 in the
output. Whay should this operation be different?Because in this case you wrap the reference you change (slot 0 in the array) into another object (the array). Therefore the reference you actually change is the same as the reference you expect to change.
If you let your resize method return the new and longer array, and assign the returned value to yor old variable, you might get a better result.
(And System.arraycopy may be more efficient than your for loop.)