ThreadLocal变量

/**
 * ThreadLocal和线程同步机制都是为了解决多线程中相同变量的访问冲突问题。 
 * ThreadLocal为每一个线程提供一个独立的变量副本，从而隔离了多个线程对访问数据的冲突。
 */
public class SequenceNumber {
    
    //①通过匿名内部类覆盖ThreadLocal的initialValue()方法，指定初始值
	private static ThreadLocal<Integer> seqNum = new ThreadLocal<Integer>(){
		public Integer initialValue(){
			return 0;
		}
	};
 
    //②获取下一个序列值
	public int getNextNum(){
		seqNum.set(seqNum.get()+1);
		return seqNum.get();
	}

	public static void main(String[ ] args) {
	     SequenceNumber sn = new SequenceNumber();
	     //③ 3个线程共享sn，各自产生序列号
	     TestClient t1 = new TestClient(sn);  
	     TestClient t2 = new TestClient(sn);
	     TestClient t3 = new TestClient(sn);
	     t1.start();
	     t2.start();
	     t3.start();
	}	
	private static class TestClient extends Thread{
		private SequenceNumber sn;
		public TestClient(SequenceNumber sn) {
			this.sn = sn;
		}
		public void run(){
	        //④每个线程打出3个序列值
			for (int i = 0; i < 3; i++) {
				System.out.println("thread["+Thread.currentThread().getName()+"] sn["+sn.getNextNum()+"]");
			}
		}
	}
}