More on Singletons – Bill Pugh Solution

On the subject of Singleton patterns I felt the need to mention Bill pugh solution or the Lazy Initialization Holder Class idiom, which is a lazy-loaded singleton. I recommend to use this when the instantiation is expensive and it is not safe to do it on time of class loading.

public class Singleton {
 private Singleton() {}
 
 private static class LazyHolder {
  private static final Something INSTANCE = new Singleton();
 }
 
 public static Singleton getInstance() {
  return LazyHolder.INSTANCE;
 }
}

It will not initialize the INSTANCE before it’s needed. But if there is a risk that the instantiation will fail you should choose another idiom.

It can be used instead of the double check lock singleton which I prefer because it’s easier to read and there is no question about when the object will be created.

public class Singleton{
 private Singleton() {}

        private static SingletonINSTANCE=null;

 
 public static Singleton getInstance() {
  if(INSTANCE==null){
   synchronize(Singleton.class){
    if(INSTANCE==null) 
     INSTANCE=new Singleton();
   }
  }
  return INSTANCE;
 }
}