Beginning Games

[Len Padson]

So, how would i make a basic game like this: a 100x100 pixel square with a black dot in the center, that can be moved left/right/up/down with the arrow keys? I think I know one way to do it but I would like to get your guys's feedback! Thanks!

[Stephan van Hulst]

Welcome to CodeRanch!

Please take a look at your private messages for an important administrative issue.

Why don't you tell us about the one way that you already know?

[Len Padson]

Well I know a very limited amount about making a class that extends JComponent, and then inserting a paint method and painting individual shapes to the JComponent, and then adding the JComponent to a JFrame, and just adding keylisteners to get user input, but I would really like to see a simple example, because I just feel like my way is more tedious than it should be. And I think the other issue is all cleared up now, thanks

[Stephan van Hulst]

Tedious as it may seem, that's the way it's done. There may be some libraries out there that make this process more smooth, but I can't think of any from the top of my head.

Here's an outline that may give you some ideas. Please keep in mind that I haven't tested this code, and I haven't added performance tricks (like selective repainting and making the panel opaque).

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

final class GamePanel extends JPanel {

  private final Timer timer;
  private long lastUpdate;

  GamePanel() {
    setFocusable(true);

    addKeyListener(new KeyAdapter() {
      @Override
      public void keyPressed(KeyEvent e) {
        switch (e.getKeyCode()) {
          case KeyEvent.VK_A: doLeft (true); break;
          case KeyEvent.VK_D: doRight(true); break;
          case KeyEvent.VK_W: doUp   (true); break;
          case KeyEvent.VK_S: doDown (true); break;
        }
      }

      @Override
      public void keyReleased(KeyEvent e) {
        switch (e.getKeyCode()) {
          case KeyEvent.VK_A: doLeft (false); break;
          case KeyEvent.VK_D: doRight(false); break;
          case KeyEvent.VK_W: doUp   (false); break;
          case KeyEvent.VK_S: doDown (false); break;
        }
      }
    });

    timer = new Timer(20, new ActionListener() {
      public void actionPerformed(ActionEvent e) {
        long now = System.currentTimeMillis();
        long time = now - lastUpdate;
        lastUpdate = now;

        updateScene(time);

        repaint();
      }
    });
  }

  void play() {
    lastUpdate = System.currentTimeMillis();
    timer.start();
  }

  void pause() {
    timer.stop();
  }

  private void doLeft(boolean left) {
    //
  }

  private void doRight(boolean right) {
    //
  }

  private void doUp(boolean up) {
    //
  }

  private void doDown(boolean down) {
    //
  }

  private void updateScene(long time) {
    // update the scene according to the amount
    // of time passed since the last update
  }

  @Override
  protected void paintComponent(Graphics g) {
    // repaint the current scene
  }
}

[Len Padson]

Wow. Thank you so much for taking the time to write all this code. I will go try it and let you know how it works.

[Jj Hill]

Stephan's answer is right.