GenericShuffle.java

import java.util.Arrays;
import java.util.Random;

/*
    There is normally no need to write shuffle.  There is a static method

    void Collections.shuffle (List<?> list, Random rng)

    in the java.util.Collections class, but not one in java.util.Arrays.
    In the case of an array one can use: List<T> Arrays.asList(T... a)
 */

public final class GenericShuffle {

   private static final Random RNG =
      new Random (Long.getLong ("seed", System.nanoTime()));

   // Randomly permute the elements of the array 'x'
   public static <T> void shuffle (final T[] x) {
      final int n = x.length; 
      for (int i = 0; i<n-1; i++) {
         // Randomly select a position in the range i..n-1
         final int j = i + RNG.nextInt (n-i);
         // Swap elements at position i and j
         final T t = x[j]; x[j] = x[i]; x[i] = t; 
      } 
   }

   public static void main (final String[] args) {
      System.out.println (Arrays.toString (args));
      shuffle (args);
      System.out.println (Arrays.toString (args));
   }

}