JAVA 设计模式之单例模式

时间：2015-03-01 15:46:10 阅读：172 评论：0 收藏：0 [点我收藏+]

标签：java 设计模式单列 singleton

概念：
　　java中单例模式是一种常见的设计模式，单例模式常见的有懒汉式、饿汉式。
　　单例模式有一下特点：
　　1、单例类只能有一个实例。
　　2、单例类必须自己自己创建自己的唯一实例。
　　3、单例类必须给所有其他对象提供这一实例。

　　单例模式确保某个类只有一个实例，而且自行实例化并向整个系统提供这个实例。

单列模式主要解决了一个类中只存在唯一一个对象。

要想保证对象唯一：

1、为了避免其他程序过多建立该对象，先禁止其他程序建立该对象。
　　2、为了其它程序访问该类对象，只能在本类中自定义一个对象。
　　3、为了方便其他程序方便对自定义对象的访问，可以对外提供一些访问方式。

如何实现：

1、将构造函数私有化。
　　2、在类中创建一个本类对象。
　　3、提供一个方法获取到该对象。

饿汉式：（类初始化对象就进行实例化）（线程安全，开发推荐使用）

    //饿汉式单例类.在<span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span>Singleton1 这个类初始化时，已经自行实例化   
    public class Singleton1 {  
        //私有的默认构造子  
        private Singleton1() {}  
        //已经自行实例化   
        private static final Singleton1 single = new Singleton1();  
        //静态工厂方法   
        public static Singleton1 getInstance() {  
            return single;  
        }  
    }  <span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"></span></span></span>

懒汉式：（调用方法才会进行实例化）(不推荐使用)

<font color="#000000">//1.懒汉式单例类.在<span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></font></span></font></span></span></span></span></font></span></span></span>Singleton2这个类的 <span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"></span></span></span></span></span></span></span></span></span></span></span></font></span></span></span>getInstance()方法被调用的时候实
<span style="font-family:宋体;">//   </span>例化（延时加载） （线程不安全，不推荐使用）  
public class Singleton2 {  
    //私有的默认构造子  
    private Singleton2() {}  
    //注意，这里没有final      
    private static Singleton2 single=null;  
    //静态工厂方法   
    public static Singleton2 getInstance() {  
         if (single == null) {    
             single = new Singleton2();  
         }    
        return single;  
    }  
} 

//<font color="#006600">2.加<span><span></span><span class="keyword">synchronized</span><span>  </span></span><span style="font-family:宋体;">锁</span>可解决线程不安全问题（加<span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="#FF0000"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></span></font></span></font></span></span></span></span></font></span></span></span></font></font><span style="color:#000000;"><span style="color:#006600;"><span><span class="keyword">synchronized</span><span></span></span></span></span><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span><font color="#000000"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="#FF0000"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></span></font></span></font></span></span></span></span></font></span></span></span></font><span style="color:#009900;"></span><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"></span><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"></span><font color="#000000"><font color="#006600"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="#FF0000"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></span></font></span></font></span></span></span></span></font></span></span></span>锁，效率会降低）</font>
<span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="#FF0000"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></span></font></span></font></span></span></span></span></font></span></span></span></font><pre name="code" class="java"><font color="#000000">public class Singleton2 {  
    //私有的默认构造子  
    private Singleton2() {}  
    //注意，这里没有final      
    private static Singleton2 single=null;  
    //静态工厂方法   
    public static <span><span style="color:#FF0000;"><span></span><span class="keyword">synchronized</span><span>  </span></span><span class="keyword"></span></span>Singleton2 getInstance() {  
         if (single == null) {    
             single = new Singleton2();  
         }    
        return single;  
    }  
} 

<span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="#FF0000"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:black;"><span style="font-size:14px;"><span style="color:#FF0000;"></span></span></span></span></font></span></span></font></span></span></span></font></font></span></font></span></span></span></span></font></span></span></span></font><pre name="code" class="java"><font color="#000000">//<font color="#006600"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="font-family:宋体;color:#FF0000;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></font></font><span style="color:#000000;"><span style="color:#006600;"><span><span class="keyword"><span style="font-family:宋体;">3.</span>synchronized</span><span></span></span></span></span><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span><font color="#000000"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="font-family:宋体;color:#FF0000;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></span></span></span></font></span></span></span></span></font></span></span></span></font><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"></span><font color="#000000"><font color="#006600"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="font-family:宋体;color:#FF0000;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></span></span></span></font></span></span></span></span></font></span></span></span>锁<span style="font-family:宋体;">判断次数比写法2要少，效率比写法而高，线程安全</span></font>
<span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="font-family:宋体;color:#FF0000;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></span></span></span></font></span></span></span></span></font></span></span></span></font><pre name="code" class="java"><span style="color:#000000;">public class Singleton2 {  
    //私有的默认构造子  
    private Singleton2() {}  
    //注意，这里没有final      
    private static Singleton2 single=null;  
    //静态工厂方法   
    public static <span><span class="keyword"></span></span>Singleton2 getInstance() {  
         if (single == null) { <span style="font-family:宋体;">                </span>   <span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="#FF0000"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:black;"></span></span></span></span></span></span></span></span></span></font></font></span></font></span></span></span></span></font></span></span></span></span><pre name="code" class="java"><span style="color:#000000;"></span><pre name="code" class="java"><pre name="code" class="java"><span style="color:#000000;"><span><font color="#FF0000"><span class="keyword">              synchronized</span><span>（Singleton2.class）{
<font face="宋体"> <font color="#000000">                 if(single == null){                       <span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></font></span></font></span></span></span></span></font></span></span></span></font></font></span></font></span></span><pre name="code" class="java"><pre name="code" class="java"><pre name="code" class="java"><pre name="code" class="java"><pre name="code" class="java"><span style="color:#000000;">                   single = new Singleton2(); </span>

}
} } return single; } }

以上两种方式的区别：

<span style="color:#000000;">    饿汉式单例类.在<span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span>Singleton1 这个类初始化时，对象已经自行实例化。</span>
<span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="#FF0000"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:black;"><span style="font-size:14px;"><span style="color:#FF0000;"></span></span></span></span></font></span></span></font></span></span></span></font></font></span></font></span></span></span></span></font></span></span></span><pre name="code" class="java"><font color="#000000">    懒汉式单例类.在<span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span></font></span></span></span>Singleton2这个类初始化时<span style="font-family:宋体;">对象不存在</span>，<span style="font-family:宋体;">调用</span><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding: 0px; line-height: 1.8; margin: 0px;"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"></span></span></span></span></span></span></span></span></span></span></span></span></span></span></span><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="#FF0000"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></span></font></span></font></span></span></span></span></font></span></span></span></font><span style="color:#000000;">Singleton2这个
    类</span><font color="#000000"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="font-family:宋体;color:#FF0000;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"></span></span></span></span></span></span></span></span></span></font></span></span></span></span></font></span></span></span></font><font color="#000000"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="black"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><font style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" face="宋体" color="#FF0000"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; font-family:宋体; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; color:rgb(0,128,0); padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px" lang="EN-US"><span style="font-family:宋体;color:black;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span size="3" style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="color:#009900;"><span style="font-family:宋体;padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"><span style="padding-bottom:0px; line-height:1.8; margin:0px; padding-left:0px; padding-right:0px; padding-top:0px"></span></span></span></span></span></span></span></span></span></font></span></font></span></span></span></span></font></span></span></span>getInstance()方法被调用的时候对象才实例化<span style="font-family:宋体;">。

     <span style="font-size:18px;color:#FF0000;">建议：开发使用饿汉式
    
</span></span></font>

JAVA 设计模式之单例模式

标签：java 设计模式单列 singleton

原文地址：http://blog.csdn.net/joakim_zhou/article/details/44002689

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