.clone() or Arrays.copyOf()?

Question

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 1

Update using jmh

Using jmh, I get similar results, except that clone seems to be marginally better.

Original post

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]; }