Java单例模式实现的几种方式
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2024-03-13 14:59:39
java单例模式实现的几种方式
单例模式好多书上都是这么写的:
public class singleton1 {
private sing...
java单例模式实现的几种方式
单例模式好多书上都是这么写的:
public class singleton1 { private singleton1(){ } private static singleton1 instance = null; public static singleton1 getinstance(){ if(instance == null){ instance = new singleton1(); } return instance; } }
但是实际开发中是不会这么写的,因为有一个严重的问题,多线程并发访问的时候,可能会产生多个实例!!
下面列举几个常用的方法:
1.使用synchronized 关键字
package singleton; public class singleton1 { private singleton1(){ } private static singleton1 instance = null; //多线程问题解法一,但是效率不高!因为每次调用都会加锁! public static synchronized singleton1 getinstance(){ if(instance == null){ instance = new singleton1(); } return instance; } public void print(){ system.out.println("thread_id:"+thread.currentthread().getid()); } private static object object = new object(); //很巧妙的方法,只有在null的时候加锁,之后就不加啦 public static singleton1 getinstance2(){ if(instance == null){ synchronized (object){ instance = new singleton1(); } } return instance; } }
2.加锁
package singleton; import java.util.concurrent.locks.reentrantlock; public class singleton2 { private singleton2(){ } private static reentrantlock lock = new reentrantlock(); private static singleton2 instance = null; public void print(){ system.out.println("thread_id:"+thread.currentthread().getid()); } public static singleton2 getinstance2(){ if(instance == null){ lock.lock(); if(instance == null){ //注意这里还要判断下!! instance = new singleton2(); } lock.unlock(); } return instance; } }
3.利用静态变量:
package singleton; public class singleton3 { public static void print(){ system.out.println("thread_id:"+thread.currentthread().getid()); } public static nested getnested(){ return nested.instance; } //这个是单例创建的类 static class nested{ private nested(){ } static nested instance = new nested(); } }
以上就是常用的创建单例的模式:
test测试代码:
package singleton; import singleton.singleton3.nested; public class test2 { public static void main(string[] args) { // todo auto-generated method stub nested singleton; myrunnable mm = new myrunnable(); myrunnable m1 = new myrunnable(); myrunnable2 m2 = new myrunnable2(); new thread(m1).start(); new thread(m2).start(); if(m1.singleton == m2.singleton){ //是同一个 system.out.println("是同一个"); }else{ system.out.println("不是同一个"); } } } class myrunnable implements runnable{ nested singleton; @override public void run() { // todo auto-generated method stub singleton = singleton3.getnested(); singleton3.print(); } } class myrunnable2 implements runnable{ nested singleton; @override public void run() { // todo auto-generated method stub singleton = singleton3.getnested(); singleton3.print(); } }
输出:
是同一个
thread_id:11
thread_id:10
以上就是对java 单例模式的资料整理,后续继续补充相关资料,谢谢大家对本站的支持!