Question

Can someone explain why getStartScreen() is the only method in the interface Game that gets added as an unimplemented method in MrNomGame class?

public class MrNomGame extends AndroidGame 
{
     public Screen getStartScreen() 
     {
        return new LoadingScreen(this); // Instantiate class
     }
}

public abstract class AndroidGame extends Activity implements Game 
{
     AndroidFastRenderView renderView;
     Graphics graphics;
     Audio audio;
     Input input;
     FileIO fileIO;
     Screen screen;
     WakeLock wakeLock;

@Override
    public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    requestWindowFeature(Window.FEATURE_NO_TITLE);
    getWindow().setFlags(WindowManager.LayoutParams.FLAG_FULLSCREEN,
            WindowManager.LayoutParams.FLAG_FULLSCREEN);

    boolean isLandscape = getResources().getConfiguration().orientation == Configuration.ORIENTATION_LANDSCAPE;
    int frameBufferWidth = isLandscape ? 480 : 320;
    int frameBufferHeight = isLandscape ? 320 : 480;
    Bitmap frameBuffer = Bitmap.createBitmap(frameBufferWidth,
            frameBufferHeight, Config.RGB_565);

    float scaleX = (float) frameBufferWidth
            / getWindowManager().getDefaultDisplay().getWidth();
    float scaleY = (float) frameBufferHeight
            / getWindowManager().getDefaultDisplay().getHeight();

    renderView = new AndroidFastRenderView(this, frameBuffer);
    graphics = new AndroidGraphics(getAssets(), frameBuffer);
    fileIO = new AndroidFileIO(this);
    audio = new AndroidAudio(this);
    input = new AndroidInput(this, renderView, scaleX, scaleY);
    screen = getStartScreen();  //unimplemented method from MrNomGame
    setContentView(renderView);

    PowerManager powerManager = (PowerManager) getSystemService(Context.POWER_SERVICE);
    wakeLock = powerManager.newWakeLock(PowerManager.FULL_WAKE_LOCK, "GLGame");
}

@Override
public void onResume() {
    super.onResume();
    wakeLock.acquire();
    screen.resume();
    renderView.resume();
}

@Override
public void onPause() {
    super.onPause();
    wakeLock.release();
    renderView.pause();
    screen.pause();

    if (isFinishing())
        screen.dispose();
}

public Input getInput() {
    return input;
}

public FileIO getFileIO() {
    return fileIO;
}

public Graphics getGraphics() {
    return graphics;
}

public Audio getAudio() {
    return audio;
}

public void setScreen(Screen screen) {
    if (screen == null)
        throw new IllegalArgumentException("Screen must not be null");

    this.screen.pause();
    this.screen.dispose();
    screen.resume();
    screen.update(0);
    this.screen = screen;
}

public Screen getCurrentScreen() {
    return screen;
}

}

public interface Game 
{
    public Input getInput();
    public FileIO getFileIO();
    public Graphics getGraphics();
    public Audio getAudio();
    public void setScreen(Screen screen);
    public Screen getCurrentScreen();
    public Screen getStartScreen();
}

Answer 1

MrNomGame class extends an abstract class AndroidGame. As MrNomGame is a concrete class, it must implement all abstract methods of its parent. Abstract class AndroidGame has no implementation of getStartScreen() method and because of this, it gets added as an unimplemented method in MrNomGame class.