How do I do a deep copy of a 2d array in Java?

Question

I just got bit by using .clone() on my 2d boolean array, thinking that this was a deep copy.

How can I perform a deep copy of my boolean[][] array?

Should I loop through it and do a series of System.arraycopy's?

Answer 1

Yes, you should iterate over 2D boolean array in order to deep copy it. Also look at java.util.Arrays#copyOf methods if you are on Java 6.

I would suggest the next code for Java 6:

public static boolean[][] deepCopy(boolean[][] original) {
    if (original == null) {
        return null;
    }

    final boolean[][] result = new boolean[original.length][];
    for (int i = 0; i < original.length; i++) {
        result[i] = Arrays.copyOf(original[i], original[i].length);
        // For Java versions prior to Java 6 use the next:
        // System.arraycopy(original[i], 0, result[i], 0, original[i].length);
    }
    return result;
}

Answer 2

Yes, that's the only way to do it. Neither java.util.Arrays not commons-lang offer deep copy for arrays.

Answer 3

I'm a fan of the Arrays utility. It has a copyOf method that will do a deep copy of a 1-D array for you, so you'd want something like this:

//say you have boolean[][] foo;
boolean[][] nv = new boolean[foo.length][foo[0].length];
for (int i = 0; i < nv.length; i++)
     nv[i] = Arrays.copyOf(foo[i], foo[i].length);