1 public class Singleton {
   2   private static Singleton INSTANCE = null;
   3 
   4   // Private constructor suppresses
   5   private Singleton() {
   6     initialize();
   7   }
   8 
   9   protected void initialize() {
  10     // Your code here
  11   }
  12 
  13   //synchronized creator to defend against multi-threading issues
  14   //another if check here to avoid multiple instantiation
  15   private synchronized static void createInstance() {
  16     if (INSTANCE == null) {
  17       INSTANCE = new Singleton();
  18     }
  19   }
  20 
  21   /**
  22    * @return The unique instance of this class.
  23    */
  24   public static Singleton getInstance() {
  25     if (INSTANCE == null) {
  26       createInstance();
  27     }
  28     return INSTANCE;
  29   }
  30 }

   1 class Singleton {
   2   private Vector v;
   3   private boolean inUse;
   4   private static Singleton instance = new Singleton();
   5 
   6   private Singleton() {
   7     v = new Vector();
   8     inUse = true;
   9     //...
  10   }
  11 
  12   public static Singleton getInstance() {
  13     return instance;
  14   }
  15 }