变量值得共享可以使用public static变量的形式，所有的线程都使用同一个public static变量。如果想实现每一个线程都有自己的共享变量该如何解决呢？JDK中提供的ThreadLocal正是解决这样的问题。
ThreadLocal主要解决的就是每个线程绑定自己的值，可以将ThreadLocal类比喻成全局存放数据的盒子，盒子中可以存储每个线程的私有数据。ThreadLocal解决的是变量在不同线程键的隔离性，也就是不同 线程拥有自己的值，不同线程中的值是可以放入ThreadLocal类中进行保存的。
package org.github.lujiango;
public class Test03 {
public static ThreadLocal<Object> tl = new ThreadLocal<Object>();
static class ThreadA extends Thread {
@Override
public void run() {
try {
tl.set("ThreadA");
Thread.sleep(200);
System.out.println("ThreadA get value = " + tl.get());
} catch (Exception e) {
e.printStackTrace();
}
}
}
static class ThreadB extends Thread {
@Override
public void run() {
try {
tl.set("ThreadB");
Thread.sleep(200);
System.out.println("ThreadB get value = " + tl.get());
} catch (Exception e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
try {
ThreadA a = new ThreadA();
ThreadB b = new ThreadB();
a.start();
b.start();
} catch (Exception e) {
e.printStackTrace();
}
}
}
第一次调用ThreadLocal类的get()方法返回值是null，可以自定义protected T initialValue()方法，设置默认值。
package org.github.lujiango;
class ThreadLocalExt extends ThreadLocal<String> {
@Override
protected String initialValue() {
return "defalut";
}
}
public class Test03 {
public static ThreadLocalExt tl = new ThreadLocalExt();
static class ThreadA extends Thread {
@Override
public void run() {
try {
System.out.println("ThreadA get value = " + tl.get());
tl.set("ThreadA");
Thread.sleep(200);
System.out.println("ThreadA get value = " + tl.get());
} catch (Exception e) {
e.printStackTrace();
}
}
}
static class ThreadB extends Thread {
@Override
public void run() {
try {
System.out.println("ThreadB get value = " + tl.get());
tl.set("ThreadB");
Thread.sleep(200);
System.out.println("ThreadB get value = " + tl.get());
} catch (Exception e) {
e.printStackTrace();
}
}
}
public static void main(String[] args) {
try {
ThreadA a = new ThreadA();
ThreadB b = new ThreadB();
a.start();
b.start();
} catch (Exception e) {
e.printStackTrace();
}
}
}
原文：http://www.cnblogs.com/lujiango/p/7580790.html