wait()方法表示，放棄當前對資源的佔有權，等啊等啊，一直等到有人通知我，我才會執行後面的程式碼。

notify()方法表示，當前的執行緒已經放棄對資源的佔有， 通知等待的執行緒來獲得對資源的佔有權，但是隻有一個執行緒能夠從wait狀態中恢復，
然後繼續執行wait()後面的語句；

notifyAll()方法表示，當前的執行緒已經放棄對資源的佔有， 通知所有的等待執行緒從wait()方法後的語句開始執行。 讀出什麼區別沒有？
wait，notify，notifyAll方法必須執行在synchronized程式碼塊內

demo

import java.util.concurrent.BrokenBarrierException;
import java.util.concurrent.CountDownLatch;
import java.util.concurrent.CyclicBarrier;
public class WaitNotifyDemo {
	static final CountDownLatch lath = new CountDownLatch(2);
	static final CyclicBarrier lathb = new CyclicBarrier(2);
	
	private static final Object syncObj = new Object();

	static class WaitThread extends Thread {
		@Override
		public void run() {
			System.out.println("wait begin enter synchronized");
			synchronized (syncObj) {
				try {
					System.out.println("wait start");
					// 執行緒等待
					syncObj.wait();
					System.out.println("wait end");
				} catch (InterruptedException e) {
					e.printStackTrace();
				}

			}
			try {
				lathb.await();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (BrokenBarrierException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			lath.countDown();
		}
	}

	static class NotifyThread extends Thread {
		@Override
		public void run() {
			try {
				Thread.sleep(10);
			} catch (InterruptedException e) {
				e.printStackTrace();
			}
			System.out.println("notify begin enter synchronized");
			synchronized (syncObj) {
				System.out.println("notify start");
				// 當前執行緒執行完畢後 喚醒wait執行緒
				syncObj.notify();

				System.out.println("notify end");

			}
			try {
				lathb.await();
			} catch (InterruptedException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			} catch (BrokenBarrierException e) {
				// TODO Auto-generated catch block
				e.printStackTrace();
			}
			lath.countDown();
		}
	}

	public static void main(String[] args) throws InterruptedException, BrokenBarrierException {

		WaitThread wd = new WaitThread();
		NotifyThread nd = new NotifyThread();
		wd.start();
		nd.start();
		
		//TODO主執行緒等待子執行緒的三種法法
		//呼叫join
		// nd.join();
		// wd.join();
		
		//呼叫CountDownLatch
		lath.await();
		
		//呼叫CyclicBarrier
		// lathb.await();
		System.out.println("=============");

	}
}