一、双检锁(Double Check Locking)

  1. package org.mlinge.s05;
  3. public class MySingleton {
  5.     //使用volatile关键字保其可见性
  6.     volatile private static MySingleton instance = null;
  8.     private MySingleton(){}
  10.     public static MySingleton getInstance() {
  11.         try {  
  12.             if(instance != null){//懒汉式 
  13.                 synchronized (MySingleton.class) {
  14.                     if(instance != null){//二次检查
  15.                         //执行操作
  16.                     }
  17.                 }
  18.             }else{
  19.                 //创建实例之前可能会有一些准备性的耗时工作 
  20.                 Thread.sleep(300);
  21.                 synchronized (MySingleton.class) {
  22.                     if(instance == null){//二次检查
  23.                         instance = new MySingleton();
  24.                     }
  25.                 }
  26.             } 
  27.         } catch (InterruptedException e) { 
  28.             e.printStackTrace();
  29.         }
  30.         return instance;
  31.     }
  32. }

二、使用静态内置类实现单例模式

  1. package org.mlinge.s06;
  3. public class MySingleton {
  5.     //内部类
  6.     private static class MySingletonHandler{
  7.         private static MySingleton instance = new MySingleton();
  8.     } 
  10.     private MySingleton(){}
  12.     public static MySingleton getInstance() { 
  13.         return MySingletonHandler.instance;
  14.     }
  15. }