Using Game Controllers with Java

In the past, I've covered using mice as input devices, and covered the general input mechanism of Listeners. I've also discussed keyboard input for console applications, and I'll soon be covering Key Bindings as a way of using the keyboard in GUI applications.

But there's no facility in Java itself that deals with game pads easily. To date, it's been necessary to create your own ActionListeners from scratch. But not any more. Thanks to the JInput project, there's an easier way to hook up game controllers to your software.

JInput attempts to do discovery on your game controller, to figure out what its setting are, what buttons and controls it has, what the center positions are of analog sticks, and so on. All that messy stuff that makes rolling your own so darn painful. It's not 100% universal, but for most controllers and most games, it will do the job admirably. If you want better for a specific controller of your own, you can extend the classes to handle your stick (and maybe feed that information back to the JInput team so that they can decide whether to include it in future releases.

It's multi-platform, Windows, Mac OS X, and Linux. So it doesn't have the limitations of a lot of the other gamepad code implementations that use native code, thus limiting themselves to one platform (usually Windows.)

If you want to see an implementation using JInput, check out Greenfoot with Gamepads. It's a good, clear example of using JInput in a general fashion.

Repetition in Java: the Timer Class

One of the things computers are best at is doing the same thing over and over again. They can do things over again so fast that it looks like they're doing it all the time. For example, in animating a video game they are reading controls and redrawing the screen so often that it looks like they're doing it constantly.

One tool for making Java do something over and over again is the Timer class.

A Timer can make your program do something on a regular basis, like redraw the screen thirty times a second, or sound a klaxon every two seconds until you go mad.

Here's a simple example of using Timer to print a message to the console once every second:

import java.util.*;

public class TimerTest {
    public static void main(String[] arg){
        Timer tickTock = new Timer();  // Create a Timer object
        TimerTask tickTockTask = new TimerTask(){
           // This is what we want the Timer to do once a second.
            public void run(){
             System.out.println("Tick");
             System.out.println("Tock");
            }
        };

        tickTock.schedule(tickTockTask, 1000, 1000);
    }
}

I've used a shortcut here to override the run() method of the TimerTask. In TimerTask the run() method is abstract, so you create a definition for it for your instance of a TimerTask. Or for a class that extends TimerTask.

In the schedule() method, we set an initial delay time of 1000 milliseconds (one second) and a repeat time of 1000 milliseconds. When run, the program will do what we told it to do in the TimerTask's run() method once every second.

If you use timer in a simple video game, replace the System.out.println() statements in run() with your game loop commands. Then set the schedule() method's repeat rate to whatever you want, for example, use a repeat rate of 33 for about 30 frames per second.

The Timer is not necessarily the best way to do this for all applications, but it's adequate if your demands aren't too great. The Timer makes use of "threads", which is a way of letting a program do more than one thing at a time. For more intensive applications that need an ability to run in a loop, the Thread class and Runnable interface can do more than a simple Timer and TimerTask.

Listeners: Can Java Hear You?

In the program given in Simple Mouse Interaction in Java we used a Listener to connect our program to the mouse. We were able to use the Listener to find out when and where the mouse had been clicked within our program's window. We used this information to draw lines in the window, in a similar fashion to our earlier programs but controlled by the mouse, rather than from specific drawing instructions in the program that do the same thing every time you run the program.

By implementing the MouseListener interface, we were able to talk to the mouse very easily. However, a MouseListener is just one of the many types of Listener available in Java.

What Sort of Listener Are You?

If we tried to implement a full graphical interface in a program by using MouseListener, we'd have a lot of work to do. We'd have to draw all the buttons using drawing instructions in our program, then wait for mouse clicks. Once we got a click on something we'd have to figure out what had been clicked on by the location of the click in our window. Then we'd have to redraw the button (or slider, or whatever) to show that it had been clicked. Then we'd have to continue responding to the mouse by figuring out what the user is doing (clicking and releasing, clicking and dragging, or what) and make our program and the picture on the screen respond appropriately.

Whew! What a lot of work that would be! If we had to do that it'd almost be enough to drive you back to the command line. (Once upon a time you did have to do all that, believe it or not. Thank goodness those days are gone.)

Fortunately, Java has a number of different types of Listener suited for different tasks that take care of the complexity for you, and let your program do what you want it to do without you having to spell out every little detail. There are listeners for buttons, sliders and other controls such as trees, lists, focus changes, and so on. You can also write your own Listeners, so that you can create a new type of control and only ever have to deal with the inner complexities of how it works once.

What is a Listener?

A Listener is a connection between your program and something that creates an Event. An Event is a communication from a device on the computer or a program to something outside itself on the computer, like another program or device (through a program associated with that device, like its device driver.) In the case of our mouse program, the Listener is the connection between the mouse's button and our program. Whenever the left button is clicked, an Event is generated that contains what happened (a left-click) and the location in our window where it happened.

If the click happens outside our program's window, an Event is generated, but our program isn't included in the recipients of the message. If our program doesn't have a Listener, the mouse click Event gets passed to our program but is ignored.

If we have a Listener appropriate to an Event that's passed to our program, then something happens with it. So we have to create a Listener, tell our program to add it to its list of Listeners (which also tells the program what kind of events it's listening for.) Then our program will tell that Listener whenever one of those events happens, and pass along the details.

A MouseListener is a very generalized sort of Listener. An ActionListener, however, can be set up to listen for a specific event, like a click on a specific button. Take a look in the Java API at ActionListener. By associating an ActionListener with a specific button, you can hear only about when that button is clicked, and know that that's precisely what happened. That ActionListener won't hear about clicks elsewhere, you don't need to check the location of the click, and it won't tell you about anything else you don't want to hear about.

That saves you all the trouble that I talked about above. You can set up your ActionListener to just exeecute the part of your code you want it to run when someone clicks the button. Or slides the slider, or whatever. No fuss, no muss.

I'll be posting a sample program soon, until then have a look at the Sun Java Tutorials on using buttons and other controls from Swing (Java's best set of graphical user interface objects.)