Java启动线程问题

Question

Here's just part of my code, if you guys would need whole code, let me know.So my issue is, that this part if(shoot) thread.start(); actually doesn't work as I'd like it to work.Using KeyListener boolean variable shoot becomes true after pressing space key.If I use just thread.start() everything works fine, but I don't want to start thread on program launch, but after pressing space button(after variable shoot becomes true).Thank you for suggenstions!

public void paintComponent(Graphics g){
super.paintComponent(g);

i=new ImageIcon("C:\\Users\\Jakub\\Desktop\\pm.gif");
pacman=i.getImage();

g.drawImage(pacman,x,y,this);

if(shoot){
g.drawOval(newX+20,y+10,10,10);
}

if(repaint)
    repaint();
 }

public static void main(String args[]){
Buffer z= new Buffer();
z.setBackground(Color.cyan);

frame=new JFrame();
frame.setSize(500,500);
frame.add(z);
frame.addKeyListener(z);
frame.setVisible(true);

thread=new Thread(){
    public void run(){
        try{
        for (int i=0;i<=20;i++){
            newX=newX+i;
            repaint=true;
            Thread.sleep(100);                
            }
    }catch(InterruptedException v){System.out.println(v);}
    }
};
if(shoot)
    thread.start();
}
    if(e.getKeyCode()==KeyEvent.VK_SPACE){
    shoot=true;
}

Answer 1

    if(shoot)
        thread.start();
=>  }

After you start your application, it creates a new JFrame, sets its size etc., creates a Thread instance, checks if shoot is true, it is false thus does not start the thread. Afterwards it waits at the point provided above for JFrame to be closed. When you click shoot , your application is still waiting at that point so it never checks if shoot is true or false.

What you can do instead would be moving the code above into your key listening method. Don't forget to move shoot into appropriate place too.

Answer 2

您可以执行在keyPressed（）方法本身中启动线程的任务，而不是在按下键时使变量为true。