不要通过在诸如JPanel之类的组件上调用getGraphics来获取Graphics对象，因为获得的Graphics对象将不会在下一次重绘时持续存在（这很可能是问题的根源）。
相反，可以考虑在BufferedImage中进行所有绘制， 然后
可以对自己的内心使用getGraphics（）。如果执行此操作，请在完成绘制后不要忘记处理Graphics对象。
例如，
import java.awt.*;import java.awt.event.*;import java.awt.image.BufferedImage;import javax.swing.JPanel;@SuppressWarnings("serial")public class MyPaint extends JPanel { public static final int IMG_WIDTH = 400; public static final int IMG_HEIGHT = IMG_WIDTH; private BufferedImage image = new BufferedImage(IMG_WIDTH, IMG_HEIGHT, BufferedImage.TYPE_INT_ARGB); public MyPaint() { MyMouseAdapter myMouseAdapter = new MyMouseAdapter(); addMouseListener(myMouseAdapter); addMouseMotionListener(myMouseAdapter); } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); if (image != null) { g.drawImage(image, 0, 0, null); } } @Override public Dimension getPreferredSize() { return new Dimension(IMG_WIDTH, IMG_HEIGHT); } public void clearScreen() { Graphics g = image.getGraphics(); g.setColor(Color.black); g.fillRect(0, 0, image.getWidth(), image.getHeight()); g.dispose(); repaint(); } private class MyMouseAdapter extends MouseAdapter { // pre to draw on the buffered image. // Don't forget to call repaint() on the "this" JPanel }}
