ThreadLocal
线程局部变量  线程本地变量
每一个线程都有一份变量的副本 互相不影响 空间换时间 



public class ThreadLocalDemo {

	static ThreadLocal<Integer> threadLocalSeq = new ThreadLocal<Integer>() {
		@Override
		protected Integer initialValue() {
			return 0;
		}
	};

	public static void main(String[] args) throws Exception {

		for (int i = 0; i < 3; i++) {
			MyThread t = new MyThread();
			t.setName("mythread" + i);
			t.start();
		}
	}

	private static class MyThread extends Thread {
		public void run() {
			for (int i = 0; i < 3; i++) {
				try {
					Thread.sleep(1000);
				} catch (Exception e) {
					System.out.println("sleep error," + e);
				}
				int seq = threadLocalSeq.get();
				System.out.println(Thread.currentThread().getName() + ":" + seq);
				threadLocalSeq.set(seq + 1);
			}
			System.out.println(Thread.currentThread().getName()+" done!");
		}
	}
}




ThreadLocal实现原理


public void set(T value) {
    Thread t = Thread.currentThread();
    // 获取线程的ThreadLocalMap 
    ThreadLocalMap map = getMap(t);
    if (map != null)
        map.set(this, value);
    else
        // map为空，创建
        createMap(t, value);
}
ThreadLocalMap getMap(Thread t) {
    return t.threadLocals;
}
void createMap(Thread t, T firstValue) {
    t.threadLocals = new ThreadLocalMap(this, firstValue);
}


完整例子代码
https://gitee.com/dyyx/hellocode/blob/master/src/dyyx/conc/ThreadLocalDemo.java