Synchronized和ThreadLocal的区别

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关于理论知识，以下这两个文章讲的很好：

Spring单例与线程安全小结

ThreadLocal的原理和在框架中的应用

不多说，上代码，自己运行一下就知道区别了

package com.spri.test;public class SequenceNumber {public Object obj = new Object();// ①通过匿名内部类覆盖ThreadLocal的initialValue()方法，指定初始值private static ThreadLocal<Integer> seqNum = new ThreadLocal<Integer>() {public Integer initialValue() {return 0;}};public int getCount(){synchronized(obj){return count++;}}public int getAno(){ano++;return ano;}public int ano = 0;public int count =0;//②获取下一个序列值public int getNextNum() {seqNum.set(seqNum.get() + 1);return seqNum.get();}public static void main(String[] args) {SequenceNumber sn = new SequenceNumber();//③3个线程共享sn，各自产生序列号TestClient t1 = new TestClient(sn);TestClient t2 = new TestClient(sn);TestClient t3 = new TestClient(sn);t1.start();t2.start();t3.start();}private static class TestClient extends Thread {private int num = 0;private SequenceNumber sn;public TestClient(SequenceNumber sn) {this.sn = sn;}public void run() {for (int i = 0; i < 3; i++) {// ④每个线程打出3个序列值System.out.println("thread[" + Thread.currentThread().getName() + "] sn[" + sn.getNextNum() + "]");System.out.println(sn.getCount());System.out.println(sn.getAno());}}}}

结果：

thread[Thread-0] sn[1]
thread[Thread-2] sn[1]
1
1
thread[Thread-1] sn[1]
2
2
thread[Thread-2] sn[2]
3
3
0
4
thread[Thread-2] sn[3]
4
5
thread[Thread-1] sn[2]
5
6
thread[Thread-0] sn[2]
6
7
thread[Thread-1] sn[3]
7
8
thread[Thread-0] sn[3]
8
9

readLocal不是为了解决并发同步用的，是为了隔离变量用的。同步是为了让多个线程共同操作一个对象而不乱掉，而ThreadLocal直接就把某个对象在各自线程中重新实例化一个了，各个线程都有自己的该对象，所以就不用管同步不同步了

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