并发控制(3） 使用double check方式的单例，来确保并发下的线程安全的单例模式

这是实现并发下懒汉模式，是线程安全的，叫做double check，另外一种是内部静态类，它们都可以实现多线程下的安全单例

package com.bjsxt.base.conn011; 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(1000); } 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(); } }