Java并发编程之ThreadLocal类

import java.util.Collections;
import java.util.HashMap;
import java.util.Map;
 
public class SimpleThreadLocal<T> {
	private Map<Thread, T> valueMap = Collections
			.synchronizedMap(new HashMap<Thread, T>());
 
	public void set(T newValue) {
		valueMap.put(Thread.currentThread(), newValue); // ①键为线程对象，值为本线程的变量副本
	}
 
	public T get() {
		Thread currentThread = Thread.currentThread();
		T o = valueMap.get(currentThread); // ②返回本线程对应的变量
		if (o == null && !valueMap.containsKey(currentThread)) { // ③如果在Map中不存在，放到Map中保存起来。
			o = initialValue();
			valueMap.put(currentThread, o);
		}
		return o;
	}
 
	public void remove() {
		valueMap.remove(Thread.currentThread());
	}
 
	protected T initialValue() {
		return null;
	}
}

class Count {
	private SimpleThreadLocal<Integer> count = new SimpleThreadLocal<Integer>() {
		@Override
		protected Integer initialValue() {
			return 0;
		}
	};
 
	public Integer increase() {
		count.set(count.get() + 1);
		return count.get();
	}
 
}
 
class TestThread implements Runnable {
	private Count count;
 
	public TestThread(Count count) {
		this.count = count;
	}
 
	@Override
	public void run() {
		// TODO Auto-generated method stub
		for (int i = 1; i <= 3; i++) {
			System.out.println(Thread.currentThread().getName() + "\t" + i
					+ "th\t" + count.increase());
		}
	}
}
 
public class TestThreadLocal {
	public static void main(String[] args) {
		Count count = new Count();
		Thread t1 = new Thread(new TestThread(count));
		Thread t2 = new Thread(new TestThread(count));
		Thread t3 = new Thread(new TestThread(count));
		Thread t4 = new Thread(new TestThread(count));
		t1.start();
		t2.start();
		t3.start();
		t4.start();
	}
}