Java array passing reference instead of value

Question

So I have a one-dimensional boolean array representing a two-dimensional shape. It's numbered from 0-8, representing a 3x3 square with this index:

012
345
678

I wrote a function to rotate the shape clockwise using the following code:

newShape[2]=oldShape[0];
newShape[5]=oldShape[1];
newShape[8]=oldShape[2];
newShape[1]=oldShape[3];
newShape[4]=oldShape[4];
newShape[7]=oldShape[5];
newShape[0]=oldShape[6];
newShape[3]=oldShape[7];
newShape[6]=oldShape[8];

Now, when the input of the function is:

false-true-false
true--true-false
false-false-false

The expected output would be:

false-true-false
false-true--true
false-false-false

However, I instead get:

false-true-false
true--true--true
false-true-false

This is not only the result of newShape, but also the result of oldShape, even though I never change oldShape. It would seem that the assignments are changing around references to variables, but not their actual values. How can I fix this?

Answer 1

It seems that you're using the same reference to both newShape and oldShape. You should use different arrays of course. I was able to repoduce your results. Just clone the array

public class Class {
    public static void main(String[] args) {
        boolean[] oldShape = new boolean[]{
                false, true, false,
                true, true, false,
                false, false, false
        };

        // THIS DOENS TWORK
        boolean[] newShape = oldShape;

        //THIS WILL WORK
//        boolean[] newShape = new boolean[9];

        output(oldShape);

        newShape[2] = oldShape[0];
        newShape[5] = oldShape[1];
        newShape[8] = oldShape[2];
        newShape[1] = oldShape[3];
        newShape[4] = oldShape[4];
        newShape[7] = oldShape[5];
        newShape[0] = oldShape[6];
        newShape[3] = oldShape[7];
        newShape[6] = oldShape[8];

        output(newShape);
    }

    private static void output(boolean[] s) {
        for (int i = 0; i < 3; ++i) {
            for (int j = 0; j < 3; ++j) {
                System.out.print(s[i*3+j] + " ");
            }
            System.out.println();
        }
        System.out.println();
    }
}