使线程正常工作

我刚开始学习线程，并误解了它们的工作原理。使线程正常工作

这里是我的类：

public class MyThread extends Thread { 
    private static int NUM = 0; 
    private int id; 

    public MyThread() { 
     id = NUM++; 
    } 

    public static void main(String[] args) { 
     for (int i = 0; i < 10; i++) { 
      new MyThread().start(); 
     } 
    } 

    public void run() { 
     System.out.println(id + " started"); 

     try { 
      Process p = Runtime.getRuntime().exec("javac -version"); 
      p.waitFor(); 
     } catch (Exception e) { 
      System.out.println("Call a doc!"); 
     } 

     System.out.println(id + " finished"); 
    } 
} 

/* 
Just a sidenote. 
I am creating new javac process just to slow an application down. 
Simple System.out.println(…) is a way faster. 
*/

为什么我总是得到所有在第一，之后“......完成”的消息“......开始”的消息？无论我开始有多少个线程，我总会看到：

0 started 
1 started 
2 started 
3 started 
4 started 
5 started 
6 started 
7 started 
8 started 
9 started 
0 finished 
1 finished 
3 finished 
4 finished 
8 finished 
5 finished 
2 finished 
6 finished 
9 finished 
7 finished

线程的目的不是并行执行吗？
也许我需要同步一些东西？还是犯了粗心的错误？要么…？
请解释。

UPDATE：

为什么我看不到，让我们说：

0 started 
1 started 
0 finished 
2 started 
1 finished 
2 finished

谢谢大家接受治疗。

来源

2010-12-07 Mick

你的英文很好。好问题。 – sje397 2010-12-07 17:38:14

@ sje397谢谢你，先生！ – Mick 2010-12-07 17:55:03

线程是并行的。否则，在下一个“开始”之前，您会看到每个线程“已完成”。

减慢线程速度的一种简单方法是使用Thread.sleep（10 * 1000）;睡觉10秒（10,000毫秒）

编辑：一个简单的方法看到线程交错是有一个固定大小的线程池。

ExecutorService pool = Executors.newFixedThreadPool(4); 
for (int i = 0; i < 10; i++) { 
    final int id = i; 
    pool.submit(new Callable<Void>() { 
     public Void call() throws InterruptedException { 
      System.out.println(id + " started"); 
      Thread.sleep(1000); 
      System.out.println(id + " finished"); 
      return null; 
     } 
    }); 
}

打印

0 started 
1 started 
2 started 
3 started 
0 finished 
4 started 
1 finished 
5 started 
2 finished 
6 started 
3 finished 
7 started 
4 finished 
8 started 
5 finished 
6 finished 
9 started 
7 finished 
8 finished 
9 finished

来源

2010-12-07 17:33:28