Question

I have hit another wall. After getting my key input working, I have been racking my brains for hours, i want to create a pause function, so that if the same key is pressed again the timertask stops running (i.e the game is paused)

JPanel component = (JPanel)frame.getContentPane();
    component.getInputMap().put(KeyStroke.getKeyStroke("SPACE"), "space");
    component.getActionMap().put("space", (new AbstractAction(){
        public void actionPerformed(ActionEvent e){

            Timer timer = new Timer();

            timer.scheduleAtFixedRate(new TimerTask(){
            public void run(){
                    grid.stepGame();
                }
            },250, 250);



        }}));


        }

The problem is i cant use a global boolean isRunning var and switch it each time the key is pressed because the timerTask method in a nested class (so the boolean isRunning would have to be declared final to be accessed…). Any ideas on how to detect if the key is pressed again or if the game is already running so i can pause/cancel my timerTask.

Many Thanks Sam

Answer 1

Since this is a Swing game, you should be using a javax.swing.Timer or Swing Timer and not a java.util.Timer. By using a Swing Timer, you guarantee that the code being called intermittently is called on the EDT, a key issue for Swing apps, and it also has a stop method that pauses the Timer. You can also give your anonymous AbstractAction class a private boolean field to check if the key is being pressed for the first time or not.

Also, kudos and 1+ for using Key Bindings instead of a KeyListener.

e.g.,

  JPanel component = (JPanel) frame.getContentPane();
  component.getInputMap().put(KeyStroke.getKeyStroke("SPACE"), "space");
  component.getActionMap().put("space", (new AbstractAction() {
     private boolean firstPress = true;
     private int timerDelay = 250;
     private javax.swing.Timer keyTimer = new javax.swing.Timer(timerDelay , new ActionListener() {

        // Swing Timer's actionPerformed
        public void actionPerformed(ActionEvent e) {
           grid.stepGame();
        }
     });

     // key binding AbstractAction's actionPerformed
     public void actionPerformed(ActionEvent e) {
        if (firstPress) {
           keyTimer.start();
        } else {
           keyTimer.stop();
        }

        firstPress = !firstPress;
     }
  }));

Another useful option is to perform a repeating task on key press and stop it on key release, and this can be done easily by getting the keystrokes for on press and on release:

KeyStroke.getKeyStroke(KeyEvent.VK_SPACE, 0, true) // for key release
KeyStroke.getKeyStroke(KeyEvent.VK_SPACE, 0, false) // for key press

For example:

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

public class SwingTimerEg2 {
   private JFrame frame;
   private Grid2 grid = new Grid2(this);
   private JTextArea textarea = new JTextArea(20, 20);
   private int stepCount = 0;

   public SwingTimerEg2() {
      frame = new JFrame();

      textarea.setEditable(false);
      frame.add(new JScrollPane(textarea, JScrollPane.VERTICAL_SCROLLBAR_ALWAYS, 
            JScrollPane.HORIZONTAL_SCROLLBAR_NEVER));

      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
      setUpKeyBinding();
   }

   void setUpKeyBinding() {
      final int timerDelay = 250;
      final Timer keyTimer = new Timer(timerDelay, new ActionListener() {

         @Override
         public void actionPerformed(ActionEvent e) {
            grid.stepGame();
         }
      });
      JPanel component = (JPanel) frame.getContentPane();
      final int condition = JComponent.WHEN_IN_FOCUSED_WINDOW;
      final String spaceDown = "space down";
      final String spaceUp = "space up";
      component.getInputMap(condition).put(KeyStroke.getKeyStroke(KeyEvent.VK_SPACE, 0, false), spaceDown);
      component.getActionMap().put(spaceDown, (new AbstractAction() {
         public void actionPerformed(ActionEvent e) {
            keyTimer.start();
         }
      }));
      component.getInputMap(condition).put(KeyStroke.getKeyStroke(KeyEvent.VK_SPACE, 0, true), spaceUp);
      component.getActionMap().put(spaceUp, (new AbstractAction() {
         public void actionPerformed(ActionEvent e) {
            keyTimer.stop();
         }
      }));

   }

   public void doSomething() {
      textarea.append(String.format("Zap %d!!!%n", stepCount));
      stepCount ++;
   }

   private static void createAndShowGui() {
      new SwingTimerEg2();
   }

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

}

class Grid2 {
   private SwingTimerEg2 stEg;

   public Grid2(SwingTimerEg2 stEg) {
      this.stEg = stEg;
   }

   void stepGame() {
      stEg.doSomething();
   }
}