code in blog.sheimi.me: 2012-06-20-software-architecture-review-5 (1)

Singleton.java

import java.util.*;
public class Limiton {
  private static int limit = 3;
  private static Limiton[] instances = new Limiton[3];
  private static Random r = new Random();
  static {
    for (int i = 0; i < limit; i++) {
      instances[i] = new Limiton();
    }
  }
  private Limiton(){}
  public static Limiton getInstance() {
    int i = r.nextInt(limit);
    return instances[i];
  }
}

// Thread safe version

import java.util.*;
public class Limiton {
  private static int limit = 3;
  private static class LimitonHolder {
    private static Limiton[] instances = new Limiton[3];
    static {
      for (int i = 0; i < limit; i++) {
        instances[i] = new Limiton();
      }
    }
  }
  private static Random r = new Random();
  private Limiton(){}
  public static Limiton getInstance() {
    int i = r.nextInt(limit);
    return LimitonHolder.instances[i];
  }
}