很久之前就知道Threadlocal 这个东西，但没有仔细研究过源码，也没有在项目中使用过。今天准备研究下一，先来个小例子，看看Threadlocal有什么用。
package com.example.bxh.sayhello.sometest; import android.util.Log; /** * Created by bxh on 6/8/17. */ public class ThreadlocalTest { private static final String TAG = "ThreadlocalTest"; ThreadlocalTestIner mThreadlocalTestIner; public ThreadlocalTest() { this.mThreadlocalTestIner = new ThreadlocalTestIner(); } public void test() { Log.i(TAG, "thread name is "+Thread.currentThread().getName()+" and tl is " + mThreadlocalTestIner.getIntThreadLocal()); Log.i(TAG, "thread name is "+Thread.currentThread().getName()+" and val is ="+ mThreadlocalTestIner.getIntThreadLocalVal()); MyThread m = new MyThread(mThreadlocalTestIner); m.start(); try { m.join(); }catch (InterruptedException e){ Log.i(TAG, "InterruptedException is "+e.getMessage()); } Log.i(TAG, "thread name is "+Thread.currentThread().getName()+" and val is ="+ mThreadlocalTestIner.getIntThreadLocalVal()); } class ThreadlocalTestIner { public ThreadLocal<Integer> getIntThreadLocal() { return intThreadLocal; } private ThreadLocal<Integer> intThreadLocal = new ThreadLocal<Integer>() { @Override protected Integer initialValue() { return super.initialValue(); } @Override public Integer get() { return super.get(); } @Override public void set(Integer value) { super.set(value); } @Override public void remove() { super.remove(); } }; public ThreadlocalTestIner() { setIntThreadLocal(10); } public ThreadlocalTestIner(ThreadLocal<Integer> intThreadLocal) { this.intThreadLocal = intThreadLocal; } public void setIntThreadLocal(int val) { this.intThreadLocal.set(val); } public Integer getIntThreadLocalVal() { return intThreadLocal.get(); } } class MyThread extends Thread { ThreadlocalTestIner iner; public MyThread(ThreadlocalTestIner i) { this.iner = i; } @Override public void run() { Log.i(TAG, "thread name is "+Thread.currentThread().getName()+" and tl is " + iner.getIntThreadLocal()); Log.i(TAG, "thread name is "+Thread.currentThread().getName()+" and val is ="+ mThreadlocalTestIner.getIntThreadLocalVal()); iner.setIntThreadLocal(20); Log.i(TAG, "then set val ,thread name is "+Thread.currentThread().getName()+" and val is ="+ mThreadlocalTestIner.getIntThreadLocalVal()); } } }执行test方法后，打印出的log如下所示：
06-08 13:10:48.190 9997-9997/? I/ThreadlocalTest: thread name is main and tl is com.example.bxh.sayhello.sometest.ThreadlocalTest$ThreadlocalTestIner$1@d0970fd 06-08 13:10:48.190 9997-9997/? I/ThreadlocalTest: thread name is main and val is =10 06-08 13:10:48.191 9997-10035/? I/ThreadlocalTest: thread name is Thread-167 and tl is com.example.bxh.sayhello.sometest.ThreadlocalTest$ThreadlocalTestIner$1@d0970fd 06-08 13:10:48.192 9997-10035/? I/ThreadlocalTest: thread name is Thread-167 and val is =null 06-08 13:10:48.192 9997-10035/? I/ThreadlocalTest: then set val ,thread name is Thread-167 and val is =20 06-08 13:10:48.192 9997-9997/? I/ThreadlocalTest: thread name is main and val is =10通过log得知，子线程中的Threadlocal与主线程的Threadlocal 是同一个对象，但是get到的值却不同，似乎子线程对值得修改，不影响主线程的值，有猫腻…… 事实上，Threadlocal的特性就是线程之间互不影响。每个线程有自己的数据备份，在A线程中修改仅仅影响A中数据，对B线程没有影响，B中原来是什么值，还是什么值。
……需要阅读源码了…… 详见我的笔记 https://www.evernote.com/l/AUvWQwFU8s9LZo0F_fpmCoiVHYsgOPa70KY
