Java多线程--让主线程等待所有子线程执行完毕

public static void main(String[] args) throws InterruptedException {
		int threadNumber = 10;
		final long start = System.currentTimeMillis();
		CyclicBarrier barrier = new CyclicBarrier(threadNumber,new Runnable(){
			@Override
			public void run() {
				long end = System.currentTimeMillis();
				System.out.println("total time : "+(end-start)+"ms");
			}
		});
		
		 for (int i = 0; i < threadNumber; i++) {   
	            new ImportThread(barrier,i).start();   
	        }  
           
        System.out.println("main thread finished!!");   
    }  
	
	private static class ImportThread extends Thread{
		private final CyclicBarrier barrier;
		private final int threadID;
		public ImportThread(CyclicBarrier barrier,int threadID){
			this.barrier = barrier;	
			this.threadID = threadID;
		}
		
		public void run() { 
            try {
                Thread.sleep((long) (Math.random() * 10000));   
            } catch (InterruptedException e) {   
                e.printStackTrace();   
            }   
            System.out.println(String.format("threadID:[%s] finished!!", threadID));   
            try {
				barrier.await();
			} catch (InterruptedException e1) {
				e1.printStackTrace();
			} catch (BrokenBarrierException e1) {
				e1.printStackTrace();
			}
        }   
	}