Bruno Grieder Bruno Grieder - 3 months ago 21
Java Question

.clone() or Arrays.copyOf()?

In an effort to reduce mutability, should we rather use

public void setValues(String[] newVals) {

this.vals = ( newVals == null ? null : newVals.clone() );
}


or

public void setValues(String[] newVals) {

this.vals = ( newVals == null ? null : Arrays.copyOf(newVals, newVals.length) );
}

Answer

I ran a quick test for performance: clone, System.arrayCopy and Arrays.copyOf have very similar performance (jdk 1.7.06, server vm).

For details (in ms), after JIT:

clone: 68
arrayCopy: 68
Arrays.copyOf: 68

Test code:

public static void main(String[] args) throws InterruptedException,
        IOException {
    int sum = 0;
    int[] warmup = new int[1];
    warmup[0] = 1;
    for (int i = 0; i < 15000; i++) { // triggers JIT
        sum += copyClone(warmup);
        sum += copyArrayCopy(warmup);
        sum += copyCopyOf(warmup);
    }

    int count = 10_000_000;
    int[] array = new int[count];
    for (int i = 0; i < count; i++) {
        array[i] = i;
    }

    // additional warmup for main
    for (int i = 0; i < 10; i++) {
        sum += copyArrayCopy(array);
    }
    System.gc();
    // copyClone
    long start = System.nanoTime();
    for (int i = 0; i < 10; i++) {
        sum += copyClone(array);
    }
    long end = System.nanoTime();
    System.out.println("clone: " + (end - start) / 1000000);
    System.gc();
    // copyArrayCopy
    start = System.nanoTime();
    for (int i = 0; i < 10; i++) {
        sum += copyArrayCopy(array);
    }
    end = System.nanoTime();
    System.out.println("arrayCopy: " + (end - start) / 1000000);
    System.gc();
    // copyCopyOf
    start = System.nanoTime();
    for (int i = 0; i < 10; i++) {
        sum += copyCopyOf(array);
    }
    end = System.nanoTime();
    System.out.println("Arrays.copyOf: " + (end - start) / 1000000);
    // sum
    System.out.println(sum);
}

private static int copyClone(int[] array) {
    int[] copy = array.clone();
    return copy[copy.length - 1];
}

private static int copyArrayCopy(int[] array) {
    int[] copy = new int[array.length];
    System.arraycopy(array, 0, copy, 0, array.length);
    return copy[copy.length - 1];
}

private static int copyCopyOf(int[] array) {
    int[] copy = Arrays.copyOf(array, array.length);
    return copy[copy.length - 1];
}