一个例子理解threadLocal用法

/**
 * 一个例子理解threadLocal
 * 
 * 一个单例模式的类
 */
public class SingleThreadLocalTest {
    private static SingleThreadLocalTest single = new SingleThreadLocalTest();

    private ThreadLocal<String> threadLocal = new ThreadLocal<String>();
    private String str;// 用于threadLocal对比

    /**
     * 单例，保证对象只会被创建一次
     */
    private SingleThreadLocalTest() {

    }

    public static SingleThreadLocalTest getInstance() {
        return single;
    }

    public void setStr(String str) {
        this.threadLocal.set(str);// 设置threadLocal的变量
        this.str = str;// 设置全局变量
    }

    public void printStr() {
        System.out.println("threadLocal:str = " + this.threadLocal.get());
        System.out.println("str = " + str);
    }
}

public class Test {
    public static void main(String[] args) {
        SingleThreadLocalTest.getInstance().setStr("a");
        SingleThreadLocalTest.getInstance().printStr();
        new MyThread().run();
        new MyThread().start();
    }
}

class MyThread extends Thread {
    public void run() {
        SingleThreadLocalTest.getInstance().printStr();
    }
}