單例模式好多書上都是這么寫的：
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public class SingleTon1 { private SingleTon1(){ } private static SingleTon1 instance = null; public static SingleTon1 getInstance(){ if(instance == null){ instance = new SingleTon1(); } return instance; }} |
但是實(shí)際開發(fā)中是不會(huì)這么寫的，因?yàn)橛幸粋€(gè)嚴(yán)重的問題，多線程并發(fā)訪問的時(shí)候，可能會(huì)產(chǎn)生多個(gè)實(shí)例！！
下面列舉幾個(gè)常用的方法：
1.使用synchronized 關(guān)鍵字
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package singleton; public class SingleTon1 { private SingleTon1(){ } private static SingleTon1 instance = null; //多線程問題解法一，但是效率不高！因?yàn)槊看握{(diào)用都會(huì)加鎖！ 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的時(shí)候加鎖，之后就不加啦 public static SingleTon1 getInstance2(){ if(instance == null){ synchronized (object){ instance = new SingleTon1(); } } return instance; } } |
2.加鎖
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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){ //注意這里還要判斷下！！ instance = new SingleTon2(); } lock.unlock(); } return instance; }} |
3.利用靜態(tài)變量：
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package singleton; public class SingleTon3 { public static void print(){ System.out.println("thread_id:"+Thread.currentThread().getId()); } public static Nested getNested(){ return Nested.instance; } //這個(gè)是單例創(chuàng)建的類 static class Nested{ private Nested(){ } static Nested instance = new Nested(); }} |
以上就是常用的創(chuàng)建單例的模式：
Test測(cè)試代碼：
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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){ //是同一個(gè) System.out.println("是同一個(gè)"); }else{ System.out.println("不是同一個(gè)"); } }} 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(); } } |
輸出：
是同一個(gè)
thread_id:11
thread_id:10
以上就是對(duì)Java 單例模式的資料整理，后續(xù)繼續(xù)補(bǔ)充相關(guān)資料，謝謝大家對(duì)本站的支持！
原文鏈接：http://www.cnblogs.com/jycboy/p/5892185.html
