Adding an image to a null layout jpanel

Question

I am looking to add a JPEG image of Pacman to a null layout JPanel so that I can use a key listener to move the image. Here's the code I have so far:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.imageio.*;
import java.awt.image.*;
import java.io.*;

public class PacmanCharacterMovement2{
  static BufferedImage pacman;
  static int xCoor;
  static int yCoor;
  public static class PacmanPanel extends JPanel implements KeyListener {
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(pacman, xCoor, yCoor, null);
    }
    public void keyTyped(KeyEvent e) {
    }
    public void keyPressed(KeyEvent e) {
      if (e.getKeyCode() == KeyEvent.VK_UP) {
        xCoor = xCoor--;
        yCoor = yCoor;
      }
      else if (e.getKeyCode() == KeyEvent.VK_DOWN) {
        xCoor = xCoor++;
        yCoor = yCoor;        
      }
      else if (e.getKeyCode() == KeyEvent.VK_LEFT) {
        xCoor = xCoor;
        yCoor = yCoor--;      
      }
      else if (e.getKeyCode() == KeyEvent.VK_RIGHT) {
        xCoor = xCoor;
        yCoor = yCoor++;        
      }
      else{}
      repaint();
    }
    public void keyReleased(KeyEvent e) {
    }
  }
  public static void main(String[] agrs){
    try {
      pacman = ImageIO.read(new File("PacmanCharacter2.jpg"));
    } catch (IOException e) {}
    xCoor = 30;
    yCoor = 30;
    JFrame window = new JFrame ("Pacman Movement");
    JPanel pacmanPanel = new JPanel ();
    pacmanPanel.setLayout(null);

    PacmanPanel mainPanel = new PacmanPanel();

    window.setContentPane(mainPanel);
    window.setSize(600,450);
    window.setLocation(350,150);
    window.setVisible(true); 
  }                                                           
}

The image appears on the screen but it does not move.

Answer 1

you need to use key blind instead awt keyevents because awt keyevent required focus to listen to event .and also xCoor = xCoor--; not work like u expected you should use xCoor--; or xCoor = xCoor-1; . this is example for up key you can write for all arrow keys ...

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.imageio.*;
import java.awt.image.*;
import java.io.*;

public class PacmanCharacterMovement2 {

    static BufferedImage pacman;
    static int xCoor=30;
    static int yCoor;

    public static class PacmanPanel extends JPanel {

        public PacmanPanel() {
            this.getInputMap().put(KeyStroke.getKeyStroke("UP"), "doup");
            this.getActionMap().put("doup", new AbstractAction("doup") {
                public void actionPerformed(ActionEvent evt) {
                    xCoor--;
                    yCoor = yCoor;
                    repaint();
                }
            }
            );
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.drawImage(pacman, xCoor, yCoor, null);
        }


    }

    public static void main(String[] agrs) {
        try {
            pacman = ImageIO.read(new File("PacmanCharacter2.jpg"));
        } catch (IOException e) {
        }
        xCoor = 30;
        yCoor = 30;
        JFrame window = new JFrame("Pacman Movement");

        PacmanPanel mainPanel = new PacmanPanel();

        window.setContentPane(mainPanel);
        window.setSize(600, 450);
        window.setLocation(350, 150);
        window.setVisible(true);
    }
} 

Answer 2

Key events are only dispatched to the component with focus. A JPanel is not focusable by default so it will never receive key events.

The better approach is to use KeyBinding which can respond to events even when they don't have focus. See Motion Using the Keyboard for more information and working examples.