Java多线程中的单例模式两种实现方式

java;">package com.ietree.multithread.sync;public class Singletion {    private static class InnerSingletion {    private static Singletion single = new Singletion();  }  public static Singletion getInstance() {    return InnerSingletion.single;  }}

package com.ietree.multithread.sync;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) { // 这个判断很重要，如果没有那将不是单例，而是多例          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();  }}