Java get simultaneos input from key listener

Question

I am creating a simple game in which a keypressed event moves a JLabel a certain number of pixels in a JPanel.

It works without any errors and when i hit the right arrow it moves right, and so on. However, as soon as i press a second key it interrupts the original movement.

For example if i was holding down the left key (and the object was moving left) and then i hit the up arrow the object stops moving left. This is (of course) because i am using only one key event for all my key.

This obviously is not an acceptable situation because as soon as i add a second object (for another player) each player will be constantly stopping the other players movement.

So my question is this: How best can i incorporate multiple simultaneous key actions? (preferably without writing dozens of KeyAdapter's and KeyEvent's)

INFO: currently i have a second class which extends a KeyAdapter. This second class includes a KeyPressed function which then uses .getKeyCode(); to find out which key is pressed and act.

EDIT: any suggestions are welcome!

score 0 · Accepted Answer · answered Feb 19 '19 at 08:17

The solution is actually quite simple. When a key pressed event is registered store a variable that records the movement. When a key released event is registered un-store that variable.

This then means that until you release you keys the movement will continue to be registered. The solution also requires a timer in order to loop repeatedly and check if your event is running or not. You could use a delay but a separate thread is the most effective for this type of task.

First you need a global variable that can store your action:

String action = "";

Then you need a key listener to record your input and when you stop inputting:

// create key listener
addKeyListener(new KeyListener()
    {
          @Override 
          public void keyPressed(KeyEvent e)
          {         
              int keyCode = e.getKeyCode();
              String event = KeyEvent.getKeyText(keyCode);


              if (event.equals("A")) {
                  // DO YOUR EVENT IF THE KEY HAS BEEN PRESSED
                  action = "A";
              }
          }

        @Override
        public void keyTyped(KeyEvent e) {}

        @Override
        public void keyReleased(KeyEvent e) {
              int keyCode = e.getKeyCode();
              String event = KeyEvent.getKeyText(keyCode);


              if (event.equals("A")) {
                  // STOP DOING YOUR EVENT
                  action = "";
              }

         }

    });

Lastly you will need a timer thread to loop and do your action:

    // CREATE A TIMER THREAD
       Timer timer = new Timer();
       timer.schedule(new TimerTask() {

           // this is what happens every time the timer runs
           @Override
           public void run() { 
             // check if your action should be preformed
             if (action.equals("A")) {
                 // ... do something
             }

           }

       }, 0, 1000);   // 1000 MILLESECONDS = 1 SECOND

       // note: you will need to run 'timer.cancel();' at some point to end your timer

Also it is worth looking at these other topics, including this about keylistener is games. And about timer tasks.

Java get simultaneos input from key listener

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