单例设计模式

/**
 *饿汉式
 */
public class Singleton {
    private Singleton(){}
    private static Singleton instance = new Singleton();
    public static Singleton getInstance(){
        return instance;
    }
}

 /**
   *懒汉式
   */
public class Singleton {
    private Singleton(){}
    private static Singleton singleton;
    public static Singleton getInstance(){
        if (null==singleton){
            singleton=new Singleton();
        }
        return singleton;
    }
}