都是通过例子来介绍

1.饿汉单例（简单的说就是一上来就创建对象）

先创建一个单例的类MySingleton

package demo01;/** * Created by mycom on 2018/3/6. */public class MySingleton {    private static MySingleton instance = new MySingleton();    private MySingleton(){}    public static MySingleton getInstance() {        return instance;    }}

在编写线程类，并且测试

package demo01;/** * Created by mycom on 2018/3/6. */public class MyThread extends Thread {    @Override    public void run() {        System.out.println(MySingleton.getInstance().hashCode());    }    public static void main(String[] args) {        MyThread[] mts = new MyThread[10];        for(int i = 0 ; i < mts.length ; i++){            mts[i] = new MyThread();        }        for (int j = 0; j < mts.length; j++) {            mts[j].start();        }    }}

如果运行的结果所有的都是一样的，说明实验成功，

2.懒汉单例（用到的时候才会创建对象）

线程安全的---方法中声明synchronized关键字

package demo01;/** * Created by mycom on 2018/3/6. */public class MySingleton {    private static MySingleton instance = null;    private MySingleton(){}    public synchronized static MySingleton getInstance() {        try {            if(instance != null){
   //懒汉式            }else{                //创建实例之前可能会有一些准备性的耗时工作                Thread.sleep(300);                instance = new MySingleton();            }        } catch (InterruptedException e) {            e.printStackTrace();        }        return instance;    }}

package demo01;/** * Created by mycom on 2018/3/6. */public class MyThread extends Thread {    @Override    public void run() {        System.out.println(MySingleton.getInstance().hashCode());    }    public static void main(String[] args) {        MyThread[] mts = new MyThread[10];        for(int i = 0 ; i < mts.length ; i++){            mts[i] = new MyThread();        }        for (int j = 0; j < mts.length; j++) {            mts[j].start();        }    }}

3.使用静态内置类实现单例模式（对上面MySingleton的代码进行改动）

package demo01;/** * Created by mycom on 2018/3/6. */public class MySingleton {    //内部类    private static class MySingletonHandler{        private static MySingleton instance = new MySingleton();    }    private MySingleton(){}    public static MySingleton getInstance() {        return MySingletonHandler.instance;    }}

测试结果

。。。。。。。