thread.join()的用法

原文：http://www.j2medev.com/bbs/dispbbs.asp?boardid=3&Id=34846

 

 thread.join()應該是讓當前線程block住，等thread執行完之後，再繼續執行

。比如有3個線程在執行計算任務，必須等三個線程都執行完才能匯總，那麼這時候在主線程裡面讓三個線程join，最後計算結果既可。代碼顯示如下。

import
java.util.Random;

public class ThreadTest {

    public static void
main(String[] args) {
        System.out.println("in " +
Thread.currentThread().getName());
        long start =
System.currentTimeMillis();
        CounterThread[] ct = new
CounterThread[3];
        for (int i = 0; i < ct.length; i++) {
       
    ct[i] = new CounterThread();
            ct[i].start();
           
try {
                ct[i].join();
            } catch
(InterruptedException e) {
                e.printStackTrace();
       
    }
        }
        long end = System.currentTimeMillis();
       
System.out.println("join total time = " + (end - start));
        int result
= 0;
        for (int j = 0; j < ct.length; j++) {
            result
+= ct[j].getResult();
        }
        System.out.println("the result is
" + result);

    }

}

class CounterThread extends Thread
{

    public CounterThread() {
    }

    private int
result;

    public int getResult() {
        return result;
   
}

    public void run() {
        try {
            int time = (new
Random().nextInt() >>> 1) % 5000;
           
Thread.sleep(time);
           
System.out.println(Thread.currentThread().getName()
                    + "
is blocked for " + time + "ms");
        } catch (InterruptedException ex)
{

        }
        result = 5;
    }
}

輸出結果：

in
main
Thread-0 is blocked for 205ms
Thread-1 is blocked for
4226ms
Thread-2 is blocked for 4469ms
join total time = 8906
the result
is 15