public class Singleton{ private Singleton(){ } //保证可见性，防止指令重排 private volatile static Singleton singleton = null; public static Singleton getSingleton(){ //提升效率，对象已经存在就不再加锁判断 if(singleton == null){ //加同步锁 synchronized (Singleton.class){ //检查对象是否存在，不存在创建对象 if(singleton == null){ singleton = new Singleton(); } } } return singleton; } }