當函數定義爲空時，SurfaceView類的函數如何工作？

我是android新手。我是與Android帆布工作，我不知道，當它們的功能界定及在Android源代碼空SurfaceView類的功能如何做的工作。這裏是Android面視圖類的源代碼當函數定義爲空時，SurfaceView類的函數如何工作？

package android.view; 

import com.android.layoutlib.bridge.MockView; 

import android.content.Context; 
import android.graphics.Canvas; 
import android.graphics.Rect; 
import android.util.AttributeSet; 


public class SurfaceView extends MockView { 

public SurfaceView(Context context) { 
    this(context, null); 
} 

public SurfaceView(Context context, AttributeSet attrs) { 
    this(context, attrs , 0); 
} 

public SurfaceView(Context context, AttributeSet attrs, int defStyle) { 
    super(context, attrs, defStyle); 
} 

public SurfaceHolder getHolder() { 
    return mSurfaceHolder; 
} 

private SurfaceHolder mSurfaceHolder = new SurfaceHolder() { 

    @Override 
    public boolean isCreating() { 
     return false; 
    } 

    @Override 
    public void addCallback(Callback callback) { 
    } 

    @Override 
    public void removeCallback(Callback callback) { 
    } 

    @Override 
    public void setFixedSize(int width, int height) { 
    } 

    @Override 
    public void setSizeFromLayout() { 
    } 

    @Override 
    public void setFormat(int format) { 
    } 

    @Override 
    public void setType(int type) { 
    } 

    @Override 
    public void setKeepScreenOn(boolean screenOn) { 
    } 

    @Override 
    public Canvas lockCanvas() { 
     return null; 
    } 

    @Override 
    public Canvas lockCanvas(Rect dirty) { 
     return null; 
    } 

    @Override 
    public void unlockCanvasAndPost(Canvas canvas) { 
    } 

    @Override 
    public Surface getSurface() { 
     return null; 
    } 

    @Override 
    public Rect getSurfaceFrame() { 
     return null; 
    } 
}; 
}

所以如何做這項工作時，我們寫