为什么android studio不能识别“package net.simplifiedcoding.spacefighter;”码？

Question

首先，我是Android游戏编程的新手。这是GameView java类。我没有编写代码并找到其他文件，您可以访问https://www.simplifiedcoding.net/android-game-development-tutorial-1/。当我编译一切时，android studio给了我错误。那是为什么？

 package net.simplifiedcoding.spacefighter;

 import android.graphics.Paint;

 import android.content.Context;
 import android.graphics.Canvas;
 import android.graphics.Color;
 import android.view.SurfaceHolder;
 import android.view.SurfaceView;

 public class GameView extends SurfaceView implements Runnable {

volatile boolean playing;
private Thread gameThread = null;

//adding the player to this class
private net.simplifiedcoding.spacefighter.Player player;

//These objects will be used for drawing
private Paint paint;
private Canvas canvas;
private SurfaceHolder surfaceHolder;

public GameView(Context context) {
    super(context);

    //initializing player object
    player = new net.simplifiedcoding.spacefighter.Player(context);

    //initializing drawing objects
    surfaceHolder = getHolder();
    paint = new Paint();
}

@Override
public void run() {
    while (playing) {
        update();
        draw();
        control();
    }
}

private void update() {
    //updating player position
    player.update();
}

private void draw() {
    //checking if surface is valid
    if (surfaceHolder.getSurface().isValid()) {
        //locking the canvas
        canvas = surfaceHolder.lockCanvas();
        //drawing a background color for canvas
        canvas.drawColor(Color.BLACK);
        //Drawing the player
        canvas.drawBitmap(
                player.getBitmap(),
                player.getX(),
                player.getY(),
                paint);
        //Unlocking the canvas
        surfaceHolder.unlockCanvasAndPost(canvas);
    }
}

private void control() {
    try {
        gameThread.sleep(17);
    } catch (InterruptedException e) {
        e.printStackTrace();
    }
}

public void pause() {
    playing = false;
    try {
        gameThread.join();
    } catch (InterruptedException e) {
    }
}

public void resume() {
    playing = true;
    gameThread = new Thread(this);
    gameThread.start();
}

}