swing - Java KeyEvent square movement

Question

I have a piece of code in which a KeyEvent is triggered when any of the arrow keys are pressed. This in turn causes a square to move across the screen.

Now I've noticed that when I press and hold the key, the square moves but the time after the initial movement to the subsequent movements is quite long if you understand what I mean? How would I go about diminishing this time?

Thanks!

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


public class GamePanel extends JPanel{

    private final int HEIGHT = 400;
    private final int WIDTH = 600;
    private Square square;
    private Circle circle;


    public GamePanel(){

        addKeyListener(new DirectionListener());

        setBackground (Color.white);
        setPreferredSize(new Dimension(WIDTH, HEIGHT));
        setFocusable(true);

        square = new Square();


    }

    public void paintComponent(Graphics g){
        super.paintComponent(g);
        square.display(g);

    }

    public class DirectionListener implements KeyListener{


        @Override
        public void keyReleased(KeyEvent event) {}

        @Override
        public void keyTyped(KeyEvent event) {}


        @Override
        public void keyPressed(KeyEvent event) {

            switch(event.getKeyCode()){

            case KeyEvent.VK_UP:

                square.moveUp();
                break;
            case KeyEvent.VK_DOWN:

                square.moveDown();
                break;
            case KeyEvent.VK_LEFT:

                square.moveLeft();
                break;
            case KeyEvent.VK_RIGHT:

                square.moveRight();
                break;
            }
            repaint();

        }
    }
}

Answer 1

• Use a Swing Timer for the actual movement.
• Start the Timer on key press
• Stop it on key release.
• Or better still, keep the timer always running, but only moving the sprite based on the state of a map, one that holds a Direction enum key and a Boolean value.
• Better to use key bindings rather than KeyListeners.

e.g.,

import java.awt.*;
import javax.swing.*;
//!! import squarequest.sprites.*;
import java.awt.event.*;
import java.util.EnumMap;
import java.util.HashMap;
import java.util.Map;

public class GamePanel extends JPanel {
   private static final int ANIMATION_DELAY = 15;
   private final int HEIGHT = 400;
   private final int WIDTH = 600;
   private Square square;
   private EnumMap<Direction, Boolean> dirMap = new EnumMap<>(Direction.class);
   private Map<Integer, Direction> keyToDir = new HashMap<>();
   // !! private Circle circle;
   private Timer animationTimer;

   public GamePanel() {
      for (Direction dir : Direction.values()) {
         dirMap.put(dir, Boolean.FALSE);
      }
      keyToDir.put(KeyEvent.VK_UP, Direction.UP);
      keyToDir.put(KeyEvent.VK_DOWN, Direction.DOWN);
      keyToDir.put(KeyEvent.VK_LEFT, Direction.LEFT);
      keyToDir.put(KeyEvent.VK_RIGHT, Direction.RIGHT);
      // !! addKeyListener(new DirectionListener());
      setKeyBindings();
      setBackground(Color.white);
      setPreferredSize(new Dimension(WIDTH, HEIGHT));
      setFocusable(true);
      square = new Square();
      animationTimer = new Timer(ANIMATION_DELAY, new AnimationListener());
      animationTimer.start();
   }

   private void setKeyBindings() {
      int condition = WHEN_IN_FOCUSED_WINDOW;
      final InputMap inputMap = getInputMap(condition);
      final ActionMap actionMap = getActionMap();
      boolean[] keyPressed = { true, false };
      for (Integer keyCode : keyToDir.keySet()) {
         Direction dir = keyToDir.get(keyCode);
         for (boolean onKeyPress : keyPressed) {
            boolean onKeyRelease = !onKeyPress; // to make it clear how bindings work
            KeyStroke keyStroke = KeyStroke.getKeyStroke(keyCode, 0,
                  onKeyRelease);
            Object key = keyStroke.toString();
            inputMap.put(keyStroke, key);
            actionMap.put(key, new KeyBindingsAction(dir, onKeyPress));
         }
      }
   }

   public void paintComponent(Graphics g) {
      super.paintComponent(g);
      square.display(g);
   }

   // public class DirectionListener implements KeyListener {
   // @Override
   // public void keyReleased(KeyEvent event) {
   // int keyCode = event.getKeyCode();
   // if (keyToDir.keySet().contains(keyCode)) {
   // Direction dir = keyToDir.get(keyCode);
   // dirMap.put(dir, false);
   // }
   // }
   //
   // @Override
   // public void keyTyped(KeyEvent event) {
   // }
   //
   // @Override
   // public void keyPressed(KeyEvent event) {
   // int keyCode = event.getKeyCode();
   // if (keyToDir.keySet().contains(keyCode)) {
   // Direction dir = keyToDir.get(keyCode);
   // dirMap.put(dir, true);
   // }
   // }
   // }

   private class AnimationListener implements ActionListener {
      @Override
      public void actionPerformed(ActionEvent evt) {
         boolean repaint = false;
         for (Direction dir : Direction.values()) {
            if (dirMap.get(dir)) {
               square.move(dir);
               repaint = true;
            }
         }
         if (repaint) {
            repaint();
         }
      }
   }

   private class KeyBindingsAction extends AbstractAction {
      private Direction dir;
      boolean pressed;

      public KeyBindingsAction(Direction dir, boolean pressed) {
         this.dir = dir;
         this.pressed = pressed;
      }

      @Override
      public void actionPerformed(ActionEvent evt) {
         dirMap.put(dir, pressed);
      }
   }

   private static void createAndShowGUI() {
      GamePanel gamePanel = new GamePanel();
      JFrame frame = new JFrame("GamePanel");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(gamePanel);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
      gamePanel.requestFocusInWindow();
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGUI();
         }
      });
   }
}

enum Direction {
   UP(0, -1), DOWN(0, 1), LEFT(-1, 0), RIGHT(1, 0);
   private int incrX;
   private int incrY;

   private Direction(int incrX, int incrY) {
      this.incrX = incrX;
      this.incrY = incrY;
   }

   public int getIncrX() {
      return incrX;
   }

   public int getIncrY() {
      return incrY;
   }
}

class Square {
   private int x = 0;
   private int y = 0;
   private int w = 20;
   private int h = w;
   private int step = 1;
   private Color color = Color.red;
   private Color fillColor = new Color(255, 150, 150);
   private Stroke stroke = new BasicStroke(3f, BasicStroke.CAP_ROUND,
         BasicStroke.JOIN_ROUND);

   public void display(Graphics g) {
      Graphics2D g2d = (Graphics2D) g.create();
      g2d.setColor(fillColor);
      g2d.fillRect(x, y, w, h);
      g2d.setStroke(stroke);
      g2d.setColor(color);
      g2d.drawRect(x, y, w, h);
      g2d.dispose();
   }

   public void setStep(int step) {
      this.step = step;
   }

   public void move(Direction dir) {
      x += step * dir.getIncrX();
      y += step * dir.getIncrY();
   }

//   public void moveRight() {
//      x++;
//   }
//
//   public void moveLeft() {
//      x--;
//   }
//
//   public void moveUp() {
//      y--;
//   }
//
//   public void moveDown() {
//      y++;
//   }
}