懒汉模式线程不安全：
package com.ddy.singleton;
public class Singleton {
private static Singleton instance;
private Singleton(){
}
public static Singleton getInstance(){
if(instance == null){
instance = new Singleton();
}
return instance;
}
}
package com.ddy.singleton;
public class Service1 implements Runnable {
private Singleton singleton = null;
//public Set<Singleton> singles = new HashSet<>();
@Override
public void run() {
// TODO Auto-generated method stub
singleton = Singleton.getInstance();
System.out.println(singleton+","+Thread.currentThread().getName());
}
}
package com.ddy.singleton;
public class Test {
public static void main(String[] args) throws InterruptedException {
Service1 t1 = new Service1();
Service1 t2 = new Service1();
new Thread(t1).start();
new Thread(t2).start();
}
}
输出结果不一致 ，说明线程不安全
修改如下：
package com.ddy.singleton;
public class Singleton {
private static Singleton instance;
private Singleton(){
}
public static Singleton getInstance(){
if(instance == null){
synchronized (Singleton.class){
if (instance == null) { //Double Checked
instance = new Singleton();
}
}
}
return instance;
}
}
这样就做到线程安全了
单例模式 懒汉模式
原文：http://www.cnblogs.com/vincent4code/p/5935295.html
