如何在 Java 中的 JFrame 上移动 JPanel？

Question

So I want to make a simple pong like game from scratch with java. I am currently making the movement of the two paddles. However, I've got stucked at the very beginning. I am trying to set the starting position of the 2 paddles, but I can not. I was trying by setting custom layouts, but later I want to change their positions constantly by moving them of course.

I've the following code:

package com.kristof;
import javax.swing.*;
import java.awt.*;

public class Main {

    public static void main(String[] args) {
        JFrame frame = new JFrame("gEngine");
        Player playerOne = new Player();
        Player playerTwo = new Player();

        frame.add(playerOne.getMyPanel());
        frame.add(playerTwo.getMyPanel());
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setBackground(Color.RED);
        frame.setSize(1280, 720);
        frame.setResizable(false);
        frame.setVisible(true);
    }

    public static class Player {
        private JPanel myPanel;

        public Player() {
            this.myPanel = new MyPanel();
        }

        public JPanel getMyPanel() {
            return myPanel;
        }

    }

    static class MyPanel extends JPanel {
        public MyPanel() {
            setBackground(Color.BLACK);
        }
        @Override
        public void paintComponent(Graphics g) {
            // let the component be painted "natural"
            super.paintComponent(g);
            // Do custom painting
            g.setColor(Color.WHITE);
            g.fillRect(50, getHeight() / 2, 20, 120);
        }
    }

}

I've already tried changing their positions by calling the setLocation method on their myPanel s, but that did not work.

Answer 1

So you created a Player class, but you dont have the position of a player in that class.

Since the paddles will only be moving up and down we only need methods for changing the y coordinate.

  static class Player{
    int x;
    int y;

   Player(int x){this.x=x;}

   void moveUp(){y--;}
   void moveDown(){y++;}

   void drawPlayer(Graphics2D g){
       g.fillRect(x,y,40,120);
   }

}

---

Now in the class that extends JPanel (in your case MyPanel ) we can take our newly created Player class as input (by putting it in the constructor)

We can also create a timer so the frames refresh regularly. By adding players[0].moveDown; in the clock, the first paddle will move down every frame

In the paint method we can iterate over the players and display them by using the drawPlayer method in the Player class.

 MyPanel(Player[] players) {
        this.players = players;
        setBackground(Color.BLACK);

        new Timer().scheduleAtFixedRate(new TimerTask() {
            @Override
            public void run() {
                repaint();
                players[0].moveDown;
            }
        }, 300, 1000 / 60);
    }

 @Override
    public void paint(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.WHITE);

        for(Player p : players){
            p.drawPlayer((Graphics2D) g);
        }
    }

---

Now to put it all together we just need to create the players when we start the program.

Player[] players = new Player[]{
            new Player(100),
            new Player(1000)
    };
    frame.add(new PongWindow(players));

---

Here is how the code will look like all together:

 import javax.swing.*; import java.awt.*; import java.awt.event.KeyEvent; import java.awt.event.KeyListener; import java.util.Timer; import java.util.TimerTask; public class Main { public static void main(String[] args) { JFrame frame = new JFrame("gEngine"); Player[] players = new Player[]{ new Player(100), new Player(1000) }; frame.add(new PongWindow(players)); frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); frame.setBackground(Color.RED); frame.setSize(1280, 720); frame.setResizable(false); frame.setVisible(true); } static class Player{ int x; int y; Player(int x){this.x=x;} void moveUp(){y+= -8;} void moveDown(){y+= 8;} void drawPlayer(Graphics2D g){ g.fillRect(x,y,40,120); } } static class PongWindow extends JPanel { //private JPanel panel = new JPanel(); Player[] players; PongWindow(Player[] players) { this.players = players; setBackground(Color.BLACK); new Timer().scheduleAtFixedRate(new TimerTask() { @Override public void run() { repaint(); players[0].moveDown(); } }, 300, 1000 / 60); } @Override public void paint(Graphics g) { super.paintComponent(g); g.setColor(Color.WHITE); for(Player p: players){ p.drawPlayer((Graphics2D) g); } } } }