java.lang.IllegalThreadStateException

public class Threads4 {

    public static void main (String[] args) {

        new Threads4().go();

    }

    

    public void go() {

        Runnable r = new Runnable() {

            public void run() {

                System.out.print("foo");

            }

        };

        Thread t = new Thread(r);

        t.start();

        t.start();

    }

}

运行结果：

Exception in thread "main" java.lang.IllegalThreadStateException

    at java.lang.Thread.start(Unknown Source)

foo    at module_01.q021.utils.Threads4.go(Threads4.java:17)

    at module_01.q021.utils.Threads4.main(Threads4.java:6)

---------------------------------------------------------------------------

Thrown   to   indicate   that   a   thread   is   not   in   an   appropriate   state   for   the   requested   operation.   See,   for   example,   the   suspend   and   resume   methods   in  class   Thread.

-------------------------------------------

对于一个已经死亡的线程调用start，sleep之类的操作等。

因此，上面代码中，应该去掉一个 t.start() ,就 OKAY 啦

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请对比下面这一题：

Given:

1. public class Threads3 implements Runnable {

2. public void run() {

3. System.out.print("running");

4. }

5. public static void main(String[] args) {

6. Thread t = new Thread(new Threads3());

7. t.run();

8. t.run();

9. t.start(); //注意：此处只调用了一次start()，故不会出现上面一题的异常

10. }

11. }

What is the result?

A. Compilation fails.

B. An exception is thrown at runtime.

C. The code executes and prints "running".

D. The code executes and prints "runningrunning".

E. The code executes and prints "runningrunningrunning".

Answer: E