singleton_java

public final class  
{ 
    private static EagerSingleton singObj = new EagerSingleton(); 
    private (){ 
    } 
 
    public static EagerSingleton getSingleInstance(){ 
       return singObj;
    } 
}

public final class DoubleCheckedSingleton 
{ 
    private static DoubleCheckedSingleton singObj = null; 
 
    private DoubleCheckedSingleton(){ 
    } 
 
    public static DoubleCheckedSingleton getSingleInstance(){ 
          if(null == singObj ) {
             synchronized(DoubleCheckedSingleton.class){
                    if(null == singObj)
                        singObj = new DoubleCheckedSingleton();
             }
       }
    return singObj;
    } 
}

public class Singleton   
{   
    private static class SingletonHolder   
    {   
        public final static Singleton instance = new Singleton();   
    }   
  
    public static Singleton getInstance()   
    {   
        return SingletonHolder.instance;   
    }   
}