如何在jpanel上绘制不同类别​​的图形

Question

So I'm trying to make a pong game and i'm trying to draw a rectangle in the paddle class but I can't figure what I'm doing wrong. Can someone please try to help me fix the issue I have attached the entire part of my program here so it is easier for you to help me. I am also copying this so I can get this through.

Main class:

package eoypongv4;

import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.util.logging.Level;
import java.util.logging.Logger;
import javax.swing.JPanel;
import javax.swing.JFrame;

/**
 *
 * 
 */
public class EOYPongV4 extends JPanel {

    int x = 0;
    int y = 0;
    boolean isballdown = true;
    boolean isballright = true;
    HumanPaddle player1;

    private void ballMovement() {

        if (isballright == true) {
            x++;
        }
        if (isballright == false) {
            x--;
        }

        if (isballdown == true) {
            y++;
        }

        if (isballdown == false) {
            y--;
        }

        if (y == getHeight() - 20) {

            isballdown = false;

        }
        if (y == 0) {

            isballdown = true;

        }
        if (x == getWidth() - 20) {

            isballright = false;
        }

        if (x == 0) {

            isballright = true;
        }

    }

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

        g.fillOval(x, y, 20, 20);

    }

    public static void main(String[] args) {

        JFrame Frame = new JFrame("EoyPongV4");

        Frame.setVisible(true);

        Frame.setSize(1068, 720);

        EOYPongV4 pong = new EOYPongV4();
        Frame.add(pong);
        for (int i = 0; i < 1;) {
            pong.ballMovement();
            pong.repaint();

            try {
                Thread.sleep(10);
            } catch (InterruptedException ex) {
                Logger.getLogger(EOYPongV4.class.getName()).log(Level.SEVERE, null, ex);
            }
        }

    }

}

Paddle class:

    package eoypongv4;

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JPanel;
import javax.swing.JFrame;
/**
 *
 * 
 */
public class HumanPaddle extends JPanel {
     double y;
     double yVel;
    boolean upAccel;
    boolean downAccel;
    int player, x;


    public void draw(Graphics g) {
        g.setColor(Color.red);
        g.drawRect(800, 300, 20, 80);
    }

}

Answer 1

Your problem is that you're making the Paddle class extend JPanel when you shouldn't be doing that.

Only one component class should do the actual rendering, a single class that extends JPanel and that has a protected void paintComponent(Graphics g) method override. Much better is to make your Paddle class a logical class, sure one that has a public void draw(Graphics g) method that allows it to draw itself, but again all real rendering should be done within a single display JPanel's paintComponent method. Within this single JPanel call your paddle's draw method and any other drawing method of sprites that you wish to draw.

eg,

// main drawing JPanel where *true* rendering is done
public class MainPanel extends JPanel {
    private Paddle paddle1 = new Paddle( /* x and y init positions */ );
    private Paddle paddle2 = new Paddle( /* x and y init positions */ );
    private Ball ball = new Ball();

    public MainPanel() {
        // Swing Timer to drive the animation
        new Timer(TIMER_DELAY, new TimerListener()).start();
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        paddle1.draw(g);
        paddle2.draw(g);
        ball.draw(g);
        // .....
    }

    private class TimerListener implements ActionListneer {
        @Override
        public void actionPerformed(ActionEvent e) {
            // move all components here
            // check for collisions
            // do program logic

            repaint();
        }
    }
}

public interface Drawable {
    public void draw(Graphics g);
}

public class Paddle implements Drawable {
    private int x;
    private int y;

    @Override
    public void draw(Graphics g) {
        // use x and y to draw rectangle
    }

    public void moveY(....) {
        // ....
    }

}

Actually, you'd give it two Paddle variables so that both paddles can be drawn...