Why does Collections.shuffle() fail for my array?

Question

Why does my code not work?

package generatingInitialPopulation;

import java.util.Arrays;
import java.util.Collections;

public class TestShuffle {
    publi         


        

Answer 1

Try adding this line of code to your test:

List l=Arrays.asList(arr);
System.out.println(l);

You will see you are printing out a single element List.

Using Arrays.asList on a primitive array cause asList to treat the int[] as a single object rather than an array. It returns a List instead of a List. So, you are basically shuffling a single element List and so nothing really gets shuffled.

Notice that some of the answers already given are wrong because asList returns a List backed by the original array, nothing gets copied - all changes are reflected in the orginal array.