java - 从接口(interface)的方法列表中调用单个方法

Question

有人可以解释一下为什么getStartScreen()是接口(interface) Game 中唯一的方法被添加为 MrNomGame 中的未实现方法类？

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 类扩展了抽象类 AndroidGame。由于 MrNomGame 是一个具体类，因此它必须实现其父类的所有抽象方法。抽象类 AndroidGame 没有 getStartScreen() 方法的实现，因此，它被添加为 MrNomGame 类中未实现的方法。