当我运行这个非常基本的2D游戏时，我不断获得NPE。它与关键事件有关，但我不知道如何解决这个问题。有人能帮我吗？它说NPE就在这一行if (_input.up.isPressed()) {
这是InputHandler类
public class InputHandler implements KeyListener {
public InputHandler(Game game) {
game.addKeyListener(this);
}
public class Key {
private boolean pressed = false;
public void toggle(boolean isPressed) {
pressed = isPressed;
}
public boolean isPressed() {
return pressed;
}
}
// public List<Key> keys = new ArrayList<Key>();
public Key up = new Key();
public Key down = new Key();
public Key left = new Key();
public Key right = new Key();
public void keyPressed(KeyEvent e) {
toggleKey(e.getKeyCode(), true);
}
public void keyReleased(KeyEvent e) {
toggleKey(e.getKeyCode(), false);
}
public void keyTyped(KeyEvent e) {
}
public void toggleKey(int keyCode, boolean isPressed) {
if (keyCode == KeyEvent.VK_W) {
up.toggle(isPressed);
} else if (keyCode == KeyEvent.VK_S) {
down.toggle(isPressed);
} else if (keyCode == KeyEvent.VK_A) {
left.toggle(isPressed);
} else if (keyCode == KeyEvent.VK_D) {
right.toggle(isPressed);
}
}
}
这是播放器类
public class Player extends Mob {
private InputHandler _input;
private int _speed;
private int _r = 10;
private int _x, _y;
public Player(int x, int y, int speed, InputHandler input) {
super("Player", x, y, 1);
_input = input;
_speed = speed;
_x = x;
_y = y;
}
public boolean hasCollided(int dx, int dy) {
return false;
}
public void update() {
int dx = 0;
int dy = 0;
if (_input.up.isPressed()) {
dy--;
} else if (_input.down.isPressed()) {
dy++;
} else if (_input.left.isPressed()) {
dx--;
} else if (_input.right.isPressed()) {
dx++;
}
if (dx != 0 || dy != 0) {
move(dx, dy);
isMoving = true;
} else {
isMoving = false;
}
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;
}
public void render(Graphics2D g) {
g.setColor(Color.BLACK);
g.fillOval(x - _r, y - _r, 2 * _r, 2 * _r);
g.setStroke(new BasicStroke(3));
g.setColor(Color.GRAY);
g.drawOval(x - _r, y - _r, 2 * _r, 2 * _r);
g.setStroke(new BasicStroke(1));
}
}
这是创建播放器的游戏类
public class Game extends Canvas implements Runnable {
private static Game _instance;
private static final String TITLE = "ProjectG";
public static final int WIDTH = 960;
public static final int HEIGHT = WIDTH * 3 / 4;
private static final int SCALE = 1;
// to make it have a higher resolution double the width and height but half
// the scale. You are doubling the width and height but keeping the same
// window size by reducing the scale
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;
public InputHandler input;
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(Game.WIDTH / 2, Game.HEIGHT / 2, 1, input);
}
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.render(g);
}
public void draw() {
Graphics g2 = this.getGraphics();
g2.drawImage(image, 0, 0, null);
g2.dispose();
}
public Game getGame() {
return this;
}
}
答案 0 :(得分：0)
您尚未初始化input，因此您传递给
player = new Player(Game.WIDTH / 2, Game.HEIGHT / 2, 1, input);
是null。你需要在
input = new InputHandler(this);