Knuth Shuffle (aka the Fisher-Yates shuffle)

Create a random permutation of an array.

import java.util.Random;
 
public static final Random gen = new Random();
 
// version for array of ints
public static void shuffle (int[] array) {
    int n = array.length;
    while (n > 1) {
        //decrements after using the value
        int k = gen.nextInt(n--);
        int temp = array[n];
        array[n] = array[k];
        array[k] = temp;
    }
}

// version for array of references
public static void shuffle (Object[] array) {
    int n = array.length;
    while (n > 1) {
        //decrements after using the value
        int k = gen.nextInt(n--); 
        Object temp = array[n];
        array[n] = array[k];
        array[k] = temp;
    }
}