//懶漢式
public class Singleton {
    private Singleton() {
    }
    private static Singleton singleton = null;
//靜態工廠方法
    public static Singleton getInstance() {
        if (singleton == null) {
            singleton = new Singleton();
        }
        return singleton;
    }

}

  //餓漢式
public class Singleton {  

    private Singleton(){}
 

    private static final Singleton singleton=new Singleton();
//靜態工廠方法
    public static Singleton getInstance(){
        return singleton;
    }
}

單例模式之懶漢式和餓漢式