一、单例模式-singleton

        

1、饿汉式(线程安全，调用效率高，但是不能延时加载)         简单实用

public class Singleton{

       private static final Singleton singleton = new Singleton();

       private Singleton(){}

       public static Singleton getInstance(){

           return singleton;

       }
}

2.懒汉式(线程不安全，调用效率不高，但是能延时加载)

public class Singleton{

    private static Singleton singleton;//未初始化
	 
    private Singleton(){}
	 
    public static Singleton getInstance(){
        if(singleton == null){
            singleton = new Singleton();
        }
        return singleton;  
    }
}