Java JPanel中getGraphics（）中的空指针
嘿，当我试图在paintComponent中使用图形对象时，我会遇到一个NullPointerException，我不知道为什么。它仍然绘制了一次我想要的内容，但在那之后，它抛出了异常。这是密码Java JPanel中getGraphics（）中的空指针,java,jpanel,Java,Jpanel,嘿，当我试图在paintComponent中使用图形对象时，我会遇到一个NullPointerException，我不知道为什么。它仍然绘制了一次我想要的内容，但在那之后，它抛出了异常。这是密码 public class RacePanel extends JPanel implements MouseListener, ActionListener { private static final int PANEL_WIDTH = 640; private static final int P
public class RacePanel extends JPanel implements MouseListener, ActionListener
{
private static final int PANEL_WIDTH = 640;
private static final int PANEL_HEIGHT = 400;
private Timer time;
boolean firstTime;
private Rabbit hare;
public RacePanel()
{
setSize(PANEL_WIDTH, PANEL_HEIGHT);
setVisible(true);
firstTime = true;
addKeyListener(new Key());
addMouseListener(this);
hare = new Rabbit();
time = new Timer(40, this);
time.start();
}
public void paintComponent(Graphics g)
{
super.paintComponent(g);
setBackground(Color.WHITE);
g.setColor(Color.RED);
g.drawLine(0, this.getHeight(), this.getWidth()/4, this.getHeight()/2);
g.drawLine(this.getWidth()/4, this.getHeight()/2, 2*this.getWidth()/4, this.getHeight());
g.drawLine(2*this.getWidth()/4, this.getHeight(), 3*this.getWidth()/4, this.getHeight()/2);
g.drawLine(3*this.getWidth()/4, this.getHeight()/2, this.getWidth(), this.getHeight());
g.setColor(Color.PINK);
g.fillOval(hare.getPosition(), this.getHeight()-10, 10, 10);
}
@Override
public void actionPerformed(ActionEvent arg0)
{
Graphics g = getGraphics();
paintComponent(g);
hare.move();
}
public static void main(String[] args)
{
RacePanel panel = new RacePanel();
panel.setVisible(true);
JFrame frame = new JFrame();
frame.getContentPane().add(panel);
frame.setMinimumSize(panel.getSize());
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
frame.addKeyListener(panel.new Key());
frame.pack();
frame.setVisible(true);
}
}
@Override
public void actionPerformed(ActionEvent arg0)
{
Graphics g = getGraphics();
paintComponent(g);
hare.move();
}
paintComponentpaintrepaintKeyListener