10.并发编程--单例模式(饥饿模式-懒汉模式)

并发编程--单例模式(饥饿模式-懒汉模式)

1. 单例模式：

- 最常见的单例模式：饥饿模式-懒汉模式；

• 1. 饥饿模式：直接实例化对象；
• 2. 懒汉模式：调用方法时进行实例化对象。

- 还有一种经典做法：在多线程模式中，一般选择如下几种单例模式：

• 1. dubble check instance:
• 2. static inner class:

示例：Singletion.java --> static inner class:

public class Singletion {

    private static class InnerSingletion {
      private static Singletion single = new Singletion();
    }

    public static Singletion getInstance(){
      return InnerSingletion.single;
    }
}

示例：  dubble check instance:

public class DubbleSingleton {

private static DubbleSingleton ds;

    public  static DubbleSingleton getDs(){
      if(ds == null){
        try {
          //模拟初始化对象的准备时间...
          Thread.sleep(3000);
        } catch (InterruptedException e) {
          e.printStackTrace();
        }
        synchronized (DubbleSingleton.class) {
          if(ds == null){
            ds = new DubbleSingleton();
          }
        }
      }
      return ds;
    }

    public static void main(String[] args) {
      Thread t1 = new Thread(new Runnable() {
        @Override
        public void run() {
          System.out.println(DubbleSingleton.getDs().hashCode());
        }
      },"t1");
      Thread t2 = new Thread(new Runnable() {
        @Override
        public void run() {
          System.out.println(DubbleSingleton.getDs().hashCode());
        }
      },"t2");
      Thread t3 = new Thread(new Runnable() {
        @Override
        public void run() {
          System.out.println(DubbleSingleton.getDs().hashCode());
        }
      },"t3");

      t1.start();
      t2.start();
      t3.start();
    }
}