章10——面向对象编程（高级部分）——两种单例模式

代码如下：

//单例模式
//instance--实例
//该篇中记录了饿汉模式和懒汉模式
public class HungryMan {
    public static void main(String[] args) {
        Single01.say();
        Single02.say();
    }
}

class Single01{
    //只能有instance这一个实例。
    private Single01(){
        System.out.println("01created");
    };
    //private static Single01(){};
    private static Single01 instance = new Single01();

    public static Single01 getInstance(){
        return instance;
    }
    public static void say(){
        System.out.println("hello!");
    }

}

class Single02{
    private Single02(){
        System.out.println("02created");
    }
    private static Single02 instance = null;
    public static Single02 getInstance(){
        if(instance==null){
            instance = new Single02();
        }
        return instance;
    }
    public static void say(){
        System.out.println("HELLO!");
    }
}

两者区别如下：