①.從CountDownLatch的設計來看,可以做彙總的操作,例如計算員工工資,這邊啟動多個執行緒同時計算等所有執行緒執行完畢之後,計算需要發放的總額

final ConcurrentHashMap<String, Integer> resultMap = new ConcurrentHashMap<String, Integer>();
		final CountDownLatch c = new CountDownLatch(10);
		final Random r = new Random();
		for (int i = 0; i < 10; i++) {
			
			new Thread(new Runnable() {
				@Override
				public void run() {
					try {
						
						String sub =Thread.currentThread().getName().substring(Thread.currentThread().getName().indexOf("-")+1);
						System.out.println("threadName:" + Thread.currentThread().getName());
						if(Integer.parseInt(sub) %2 == 0){
							System.out.println(Thread.currentThread().getName()+" wait 2s");
							Thread.sleep(2000);
						}else{
							System.out.println(Thread.currentThread().getName()+" wait 0.5s");
							Thread.sleep(500);
							
						}
						resultMap.put(Thread.currentThread().getName(), r.nextInt(10000));
						c.countDown();
					} catch (Exception e) {
						e.printStackTrace();
					}

				}
			}).start();
		}
		

		c.await();
		System.out.println("n***********************n");
		int sum = 0;
		for(String key :resultMap.keySet()){
			Integer num = resultMap.get(key);
			sum += num;
			System.out.println(num);
			
		}
		System.out.println("end:"+sum);
 

控制檯:
threadName:Thread-2
threadName:Thread-4
Thread-2 wait 2s
threadName:Thread-3
Thread-3 wait 0.5s
threadName:Thread-6
Thread-6 wait 2s
threadName:Thread-1
Thread-1 wait 0.5s
threadName:Thread-0
Thread-0 wait 2s
Thread-4 wait 2s
threadName:Thread-8
Thread-8 wait 2s
threadName:Thread-7
Thread-7 wait 0.5s
threadName:Thread-5
Thread-5 wait 0.5s
threadName:Thread-9
Thread-9 wait 0.5s

***********************

8881
7993
3441
8408
100
1074
6542
4448
4216
2839
end:47942
 

②.CyclicBarrier可以用來做初始化操作之後,所有的執行緒統一執行:

System.out.println("init finish.");
		System.out.println("************************");
		final CyclicBarrier cb = new CyclicBarrier(10);
		for (int i = 0; i < 10; i++) {
			new Thread(new Runnable() {

				@Override
				public void run() {
					try {
						System.out.println("ThreadName:" + Thread.currentThread().getName());
						Thread.sleep(3000);
						cb.await();
						System.out.println("ThreadName:" + Thread.currentThread().getName()
						        + ",end!");
					} catch (InterruptedException | BrokenBarrierException e) {
						e.printStackTrace();
					}
				}
			}).start();
		}
 

控制檯:
init finish.
************************
ThreadName:Thread-0
ThreadName:Thread-1
ThreadName:Thread-2
ThreadName:Thread-3
ThreadName:Thread-4
ThreadName:Thread-5
ThreadName:Thread-6
ThreadName:Thread-7
ThreadName:Thread-8
ThreadName:Thread-9
ThreadName:Thread-7,end!
ThreadName:Thread-1,end!
ThreadName:Thread-2,end!
ThreadName:Thread-8,end!
ThreadName:Thread-9,end!
ThreadName:Thread-4,end!
ThreadName:Thread-3,end!
ThreadName:Thread-0,end!
ThreadName:Thread-6,end!
ThreadName:Thread-5,end!

③.Semaphore(訊號量)

    //構造方法permits表示一次性接受幾個執行緒通過,比如有20個執行緒,permits=5,那麼則表示一次性可以有五個執行緒通過,若為1那麼作用相當於是一把鎖,

   new Semaphore(permits);

acquire相當於是用來獲取一個令牌,每獲取一個令牌則減少一個,當所有令牌用完之後,剩餘執行緒進入等待,直到有其他執行緒執行完畢並且歸還令牌,剩餘執行緒準備搶奪令牌以便執行,

	ExecutorService exec = Executors.newCachedThreadPool();

		// 只能5個執行緒同時訪問

		final Semaphore semp = new Semaphore(5);
		for (int i = 0; i < 20; i++) {

			final int NO = i;

			Runnable run = new Runnable() {

				public void run() {

					try {
						// 獲取許可
						semp.acquire();
						System.out.println("No: " + (NO+1));
						Thread.sleep(2000);
						// 訪問完後，釋放
						semp.release();
						System.out.println("------------");
						System.out.println("availability:" + semp.availablePermits());
						Thread.sleep(1000);

					} catch (InterruptedException e) {

						e.printStackTrace();

					}

				}

			};

			exec.execute(run);

		}

		// 退出執行緒池

		exec.shutdown();

從控制檯可以看出,第一次5個執行緒一起執行,後面執行緒的執行受上一次執行緒執行並且釋放令牌時間的影響 ,等所有執行緒執行完畢則顯示共有五個令牌可以使用

No: 1
No: 2
No: 4
No: 3
No: 5
------------
No: 8
No: 6
------------
availability:0
------------
availability:0
------------
------------
availability:0
availability:0
availability:0
No: 10
No: 7
No: 9
No: 12
------------
availability:0
------------
No: 11
No: 13
------------
------------
availability:0
------------
availability:0
No: 15
availability:0
No: 14
availability:1
------------
No: 16
availability:0
------------
No: 18
No: 17
------------
availability:0
------------
availability:0
availability:0
No: 19
------------
No: 20
availability:0
------------
availability:1
------------
------------
availability:3
availability:3
------------
availability:4
------------
availability:5