java - 程序抛出 IllegalThreadStateException

Question

在我的乒乓球游戏中，每个对象(球和两个 Racket )都在独立线程中运行。

static Ball b = new Ball(195, 145);

Thread ball = new Thread(b);
Thread paddle1 = new Thread(b.paddle1);
Thread paddle2 = new Thread(b.paddle2);
public void startGame(){
    gameStarted = true;
    ball.start();
    paddle1.start();
    paddle2.start();
}

我想在按下 ESC 时将游戏设置为暂停，并在再次按下 ESC 时设置游戏 - 继续游戏。所以在 keyPressed 事件中我这样做了

 if (e.getKeyCode() == KeyEvent.VK_ESCAPE){
            if (gameStarted) {
                gameStarted = false;
                ballCurrentX = b.x; //save all states
                ballCurrentY = b.y;
                ballXDirection = b.xDirection;
                ballYDirection = b.yDirection;
                p1Score = b.p1Score;
                p2Score = b.p2Score;
                p1CurrentY = b.paddle1.y;
                p2CurrentY = b.paddle2.y;
                try {
                    ball.interrupt();
                    ball.join();
                    paddle1.interrupt();
                    paddle1.join();
                    paddle2.interrupt();
                    paddle2.join();
                } catch (InterruptedException e1) {
                    e1.printStackTrace();
                }   
            }
            else {
                gameStarted = true;
                continueGame();
            }
        } 

要继续游戏 - 我重新启动所有线程，但为之前游戏状态的对象设置参数

public void continueGame(){
    gameStarted = true;
    b = new Ball(ballCurrentX, ballCurrentY);
    b.xDirection = ballXDirection;
    b.yDirection = ballYDirection;
    b.p1Score = p1Score;
    b.p2Score = p2Score;
    b.paddle1.y = p1CurrentY;
    b.paddle2.y = p2CurrentY;
    ball.start();
    paddle1.start();
    paddle2.start();
}

但是程序抛出IllegalThreadStateException并且游戏无法继续。有什么问题？它不会停止线程？

Answer 1

To continue game - I restart all threads ...

您无法重新启动 Java 线程。 Thread.start() 的 javadoc声明如下:

" It is never legal to start a thread more than once. In particular, a thread may not be restarted once it has completed execution."

"Throws: IllegalThreadStateException - if the thread was already started."

您需要创建新的线程对象并启动它们，或者找出某种方法来告诉现有线程在中断时进入应用程序定义的“暂停”状态，并在那里等待，直到被告知“恢复” ”。