简单播放器不会在Java 2D游戏中显示

Question

I have having issues making my player show up. I created the Player class and implemented its draw() method in the render function of the game loop but there is no player. No errors either. Can someone help me find out why the player is not showing?

Also there is a border on the left and bottom of the window and I cannot get rid of it. Does someone know how?

here is the game class

@SuppressWarnings("serial")
public class Game extends Canvas implements Runnable {

    private static Game _instance;
    private static final String TITLE = "ProjectG";
    public static final int WIDTH = 240;
    public static final int HEIGHT = WIDTH * 3 / 4;
    private static final int SCALE = 4;
    public static final Dimension SIZE = new Dimension(WIDTH * SCALE, HEIGHT * SCALE);

    private static final int UPDATE_RATE = 60;
    private static final int RENDER_RATE = 60;

    private JFrame _frame;
    private Thread _thread;
    private boolean _running = false;

    private int _tps = 0;
    private int _fps = 0;
    private int _totalTicks = 0;

    private BufferedImage image;
    private Graphics2D g;

    private Player player;

    public Game() {
        _instance = this;

        setPreferredSize(SIZE);
        setMinimumSize(SIZE);
        setMaximumSize(SIZE);

        _frame = new JFrame(TITLE);
        _frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        _frame.setLayout(new BorderLayout());
        _frame.add(_instance, BorderLayout.CENTER);
        _frame.pack();

        _frame.setResizable(false);
        _frame.setLocationRelativeTo(null);
        _frame.setVisible(true);

        player = new Player();
    }

    public synchronized void start() {
        _running = true;
        _thread = new Thread(this, TITLE + "_main");
        _thread.start();
    }

    public synchronized void stop() {
        _running = false;

        if (_thread != null) {
            try {
                _thread.join();
            } catch (InterruptedException e) {
                e.printStackTrace();
            }
        }
    }

    public void run() {
        double lastUpdateTime = System.nanoTime();
        double lastRenderTime = System.nanoTime();

        final int ns = 1000000000;
        final double nsPerUpdate = (double) ns / UPDATE_RATE;
        final double nsPerRender = (double) ns / RENDER_RATE;
        final int maxUpdatesBeforeRender = 1;

        int lastSecond = (int) lastUpdateTime / ns;
        int tickCount = 0;
        int renderCount = 0;

        image = new BufferedImage(WIDTH * SCALE, HEIGHT * SCALE, BufferedImage.TYPE_INT_RGB);
        g = (Graphics2D) image.getGraphics();

        while (_running) {
            long currTime = System.nanoTime();
            int tps = 0;

            while ((currTime - lastUpdateTime) > nsPerUpdate && tps < maxUpdatesBeforeRender) {
                update();
                tickCount++;
                _totalTicks++;
                tps++;
                lastUpdateTime += nsPerUpdate;
            }

            if (currTime - lastUpdateTime > nsPerUpdate) {
                lastUpdateTime = currTime - nsPerUpdate;
            }

            float interpolation = Math.min(1.0F, (float) ((currTime - lastUpdateTime) / nsPerUpdate));
            render(interpolation);
            draw();
            renderCount++;
            lastRenderTime = currTime;

            int currSecond = (int) (lastUpdateTime / ns);
            if (currSecond > lastSecond) {
                _tps = tickCount;
                _fps = renderCount;
                tickCount = 0;
                renderCount = 0;
                lastSecond = currSecond;
                System.out.println(_tps + " TPS " + _fps + " FPS");
            }

            while (currTime - lastRenderTime < nsPerRender && currTime - lastUpdateTime < nsPerUpdate) {
                Thread.yield();
                try {
                    Thread.sleep(1);
                } catch (InterruptedException e) {
                    e.printStackTrace();
                }
                currTime = System.nanoTime();
            }
        }
    }

    public void update() {
        player.update();
    }

    public void render(float interpolation) {
        BufferStrategy bs = getBufferStrategy();
        if (bs == null) {
            createBufferStrategy(3);
        }

        g.setColor(Color.WHITE);
        g.fillRect(0, 0, WIDTH * SCALE, HEIGHT * SCALE);
        g.setColor(Color.BLACK);
        g.drawString("TPS: " + _fps + " FPS: " + _fps, 10, 20);

        player.draw(g);
    }

    public void draw() {
        Graphics g2 = this.getGraphics();
        g2.drawImage(image, 0, 0, null);
        g2.dispose();
    }
}

and here is the player class

public class Player {

    private int x;
    private int y;
    private int r;

    private int dx;
    private int dy;
    private int speed;

    private boolean left;
    private boolean right;
    private boolean up;
    private boolean down;

    private int lives;

    public Player() {
        x = Game.WIDTH / 2;
        y = Game.HEIGHT / 2;

        dx = 0;
        dy = 0;
        speed = 5;
        lives = 3;
    }

    public void update() {
        if (left) {
            dx = -speed;
        } else if (right) {
            dx = speed;
        } else if (up) {
            dy = -speed;
        } else if (down) {
            dy = speed;
        }

        x += dx;
        y += dy;

        if (x < r)
            x = r;
        if (y < r)
            y = r;
        if (x > Game.WIDTH - r)
            x = Game.WIDTH - r;
        if (y > Game.HEIGHT - r)
            y = Game.HEIGHT - r;

        dx = 0;
        dy = 0;
    }

    public void draw(Graphics2D g) {

        g.setColor(Color.BLACK);
        g.fillOval(x - r, y - r, 2 * r, 2 * r);

        g.setStroke(new BasicStroke(3));
        g.setColor(Color.BLACK.brighter());
        g.drawOval(x - r, y - r, 2 * r, 2 * r);
        g.setStroke(new BasicStroke(1));
    }

    public int getLives() {
        return lives;
    }
}

and here is the Main class if needed

public class Main {

    private static Game _game;

    public static void main(String[] args) {
        _game = new Game();
        _game.start();
    }
}

Answer 1

If you never initialize r it will default to 0 , and lines like the following.

g.drawOval(x - r, y - r, 2 * r, 2 * r);

won't actually draw anything.