一旦被另一个类调用，Java图形将不适用于JPanel类

Question

I created a Calculator that is supposed to prompt a game of Pong when certain keys are pressed. My pong game was created separately and runs fine by itself. However, the graphics refuse to move once it is implemented into my Calculator program.

Below is the KeyAdapter code in the Calculator program that will prompt the Pong game:

 import java.applet.Applet;
 import java.awt.List;
 import java.awt.event.KeyAdapter;
 import java.awt.event.KeyEvent;
 import java.awt.event.KeyListener;
 import java.util.ArrayList;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 import javax.swing.JFrame;

 public class Konami extends KeyAdapter {

private ArrayList<Integer> keys  = new ArrayList<Integer>();
private ArrayList<Integer> keysMarked  = new ArrayList< >();


public ArrayList init(){

    keysMarked.add(KeyEvent.VK_UP);
    keysMarked.add(KeyEvent.VK_UP);
    keysMarked.add(KeyEvent.VK_DOWN);
    keysMarked.add(KeyEvent.VK_DOWN);
    keysMarked.add(KeyEvent.VK_LEFT);
    keysMarked.add(KeyEvent.VK_RIGHT);
    keysMarked.add(KeyEvent.VK_LEFT);
    keysMarked.add(KeyEvent.VK_RIGHT);
    keysMarked.add(KeyEvent.VK_B);
    keysMarked.add(KeyEvent.VK_A);

    return keysMarked;
}




@Override
public void keyTyped(KeyEvent event) {

}


@Override
public void keyPressed(KeyEvent event) {

    Konami pong = new Konami();

                keys.add(event.getKeyCode());

                if (keys.size() == keysMarked.size()){
                     if (keys.equals(keysMarked)){
                         System.out.println("PONG GAME");

 //Here I call the Pong game:

                         JFrame newFrame = new JFrame();
                         Pong game = new Pong();
                         game.setVisible(true);
                         newFrame.setBounds(450, 170, 400, 300);
                         newFrame.setResizable(false);
                         newFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                         newFrame.add(game);

                         newFrame.setVisible(true);

                      } 
                     else 
                         keys.clear();
                }
                else if (keys.size() > keysMarked.size())
                {
                    keys.clear();
                }
}

@Override
public void keyReleased(KeyEvent event) {
}


}

Here is the code for the Pong game:

 package cs1302.calc;
 import java.awt.BorderLayout;
 import java.awt.Color;
 import java.awt.Dimension;
 import java.util.logging.*;
 import java.awt.Graphics;
 import java.awt.event.KeyEvent;
 import static java.lang.Math.abs;
 import javax.swing.JFrame;
 import javax.swing.JPanel;
 import javax.swing.JTextArea;
 import javax.swing.JTextField;

  public class Pong extends JPanel{
int x = 0;
int y = 0;

static int xP = 0;
static int yP = 150;

static int xP2 = 390;
static int yP2 = 150;

int border = 30;
boolean ballGoingDown = true;
boolean ballGoingRight = true;

private void moveBall(){

    if (ballGoingRight == true){
        x = x + 1;
    }

    if (ballGoingRight == false){
        x = x - 1;
    }


    if (ballGoingDown == true){
        y = y + 1;
    }

    if (ballGoingDown == false){
        y = y - 1;
    }

    //detects hit bottom
    if (y== getHeight() - border){
        ballGoingDown = false;
    }

    if (y== 0){
        ballGoingDown = true;
    }


    //detects hit bat
    if (abs(x-xP) <3  &&  abs(y-yP) <30 ){
        ballGoingRight = true;
    }

    if (abs(x-xP2) <23  &&  abs(y-yP2) <30 ){
        ballGoingRight = false;
    }

    //detects ball moving past border
    if (x < 0){
        System.out.println("PLAYER 2 WINS.");
        System.exit(0);
    };

    if (x > getWidth()){
        System.out.println("PLAYER 1 WINS.");
        System.exit(0);
    };

}

private void moveBat(){
    Control c = new Control();


}


@Override
public void paint(Graphics g){
    super.paint(g);
    g.setColor(Color.ORANGE);
    g.fillOval(x, y, 30, 30);

    g.setColor(Color.BLUE);
    g.fillRect(xP, yP, 10,30);


    g.setColor(Color.BLUE);
    g.fillRect(xP2, yP2, 10,30);



}




public static void main2(String s) throws InterruptedException{
        //My window code
       JFrame myFrame = new JFrame("pong");


        myFrame.setBounds(450, 170, 400, 300);
        myFrame.setResizable(false);
       myFrame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

       //My game code
       Pong game = new Pong();
       myFrame.add(game);

       game.setFocusable(true);
       game.requestFocusInWindow();
       Control control = new Control();
       game.addKeyListener(control);


       new BorderLayout();
       JTextArea textArea = new JTextArea("Player 1: S Key (up) Z Key(down)"
               + "| Player 2: Up(up) Down (down)");
       game.add(textArea, BorderLayout.PAGE_END);

       myFrame.setVisible(true);


       while (true)
       {
           game.moveBall();
           game.repaint();

           Thread.sleep(10);
       }


}

}

Lastly is the KeyAdapter class that controls the graphics within the Pong game:

 import java.awt.Graphics;
 import java.awt.event.KeyAdapter;
 import java.awt.event.KeyEvent;
 import javax.swing.JFrame;
 import javax.swing.JPanel;
 import cs1302.calc.Pong;

  public class Control extends KeyAdapter {

@Override
public void keyTyped(KeyEvent event) {

}

@Override
 public void keyPressed(KeyEvent event) {
      if (event.getKeyCode() == KeyEvent.VK_S){  

          Pong.yP = Pong.yP - 25;
      }
       if (event.getKeyCode() == KeyEvent.VK_Z){        
          Pong.yP = Pong.yP + 25;

      }

        if (event.getKeyCode() == KeyEvent.VK_UP){  
          Pong.yP2 = Pong.yP2 - 25;
      }
       if (event.getKeyCode() == KeyEvent.VK_DOWN){        
          Pong.yP2 = Pong.yP2 + 25;

      }
}

  @Override
public void keyReleased(KeyEvent event) {
}
 }

Answer 1

When you initialize Pong from the KeyListener , the code responsible for the animation is not run at all, since it's in Pong.main2() , and you don't call that code. However, don't simply call that since there are further problems with that approach:

If Pong.main() is called from anywhere else than the event dispatch thread , like you must be doing when it appears to run correctly, the Pong class initializes its UI incorrectly outside the EDT. It also runs a game loop outside the EDT (in the main thread). That later bug makes it work.

When started from a KeyListener , if you called Pong.main() , or any other method where you implemented the game loop the same way, it would block the EDT and no drawing would happen. Instead of a loop, you should use a swing Timer to handle the drawing and updates. That does not block the event dispatch thread, and it also runs the relevant code correctly in the EDT when it's the time to run it.