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public
class Singleton { private
static volatile Singleton singleton = null;//volatile阻止JVM对指令执行顺序的优化，防止乱序执行导致导致返回的实例为半成品 private
void Singleton() {} public
static Singleton getInstance() { if
(singleton == null) { synchronized
(Singleton.class) { if
(singleton == null) {//双重检查，如果第二个线程进入不做检查会产生不同的实例 singleton = new
Singleton(); } } } return
singleton; } public
static void main(String[] args) { System.out.println(Singleton.getInstance() == Singleton.getInstance()); }} |
原文：http://www.cnblogs.com/easylifesh/p/3614152.html