编辑（更新代码+问题）：
我正在创建一个 2D 自上而下的 RPG，但在绘制 32x32 的小图像（总共 256 个）时遇到了很多麻烦。不过，我已经成功地绘制了许多分级颜色的正方形。所以我可以确认嵌套的for循环映射正确。根据我附上的代码，谁能帮我理解我哪里出错了？
public class TestClass extends JPanel {
public JPanel floor;
public Point[] imgPoints;
public Image[] tileImgs;
private Dimension d = new Dimension(512, 512);
private Graphics g;
private int size;
/*
* This is the Floor class which is supposed to print level tiles
* tilesize is specified by 'int size'.
* Constructor instantiates a JPanel which is
* used inside a graphical interface (JFrame)
*/
public TestClass() throws IOException {
floor = new JPanel();
floor.setSize(new Dimension(512, 512));
floor.setMinimumSize(new Dimension(512, 512));
tileImgs = new Image[256];
int k = 0;
int xImg = 1;
for (Image x : tileImgs) {
if (xImg < 10){
tileImgs[k] = ImageIO.read(this.getClass().getResource("/hyp/hyptosis" + "00" + xImg + ".png"));
}
else if (xImg < 100 && xImg >= 10){
tileImgs[k] = ImageIO.read(this.getClass().getResource("/hyp/hyptosis" + "0" + xImg + ".png"));
}
else{
tileImgs[k] = ImageIO.read(this.getClass().getResource("/hyp/hyptosis" + xImg + ".png"));
}
k++;
}
}
public void paint(Graphics g) {
super.paint(g);
setDoubleBuffered(true);
int c = 0;
int pointCount = 0;
size = 32;
for (int i = 0; i < d.getWidth(); i += size) {
for (int j = 0; j < d.getHeight(); j += size) {
pointCount++;
}
}
c = 0;
Point[] imgPoints = new Point[pointCount];
for (int i = 0; i < d.getWidth(); i += size) {
for (int j = 0; j < d.getHeight(); j += size) {
imgPoints[c] = (new Point(i, j));
c++;
}
}
paintComponent();
}
// Paint level-tiles.
private void paintComponent() {
int k = 0;
for (Point q : imgPoints) {
q = imgPoints[k];
ImageObserver imgObs = null;
int xx = (int) q.getX();
int yy = (int) q.getY();
g.drawImage(tileImgs[k], xx, yy, imgObs);
this.imageUpdate(tileImgs[k], FRAMEBITS, xx, yy, size, size);
repaint();
k++;
}
}
}
来自控制台的错误日志：
> Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.JComponent.paintComponent(Unknown Source)
at gameObjects.TestClass.paintComponent(TestClass.java:82)
at gameObjects.TestClass.paint(TestClass.java:76)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JLayeredPane.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paintToOffscreen(Unknown Source)
at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
at javax.swing.RepaintManager.paint(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at java.awt.GraphicsCallback$PaintCallback.run(Unknown Source)
at sun.awt.SunGraphicsCallback.runOneComponent(Unknown Source)
at sun.awt.SunGraphicsCallback.runComponents(Unknown Source)
at java.awt.Container.paint(Unknown Source)
at java.awt.Window.paint(Unknown Source)
at javax.swing.RepaintManager$4.run(Unknown Source)
at javax.swing.RepaintManager$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.access$1200(Unknown Source)
at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at javax.swing.JComponent.paintComponent(Unknown Source)
at gameObjects.TestClass.paintComponent(TestClass.java:82)
at gameObjects.TestClass.paint(TestClass.java:76)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at javax.swing.JLayeredPane.paint(Unknown Source)
at javax.swing.JComponent.paintChildren(Unknown Source)
at javax.swing.JComponent.paintToOffscreen(Unknown Source)
at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
at javax.swing.RepaintManager.paint(Unknown Source)
at javax.swing.JComponent.paint(Unknown Source)
at java.awt.GraphicsCallback$PaintCallback.run(Unknown Source)
at sun.awt.SunGraphicsCallback.runOneComponent(Unknown Source)
at sun.awt.SunGraphicsCallback.runComponents(Unknown Source)
at java.awt.Container.paint(Unknown Source)
at java.awt.Window.paint(Unknown Source)
at javax.swing.RepaintManager$4.run(Unknown Source)
at javax.swing.RepaintManager$4.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
at javax.swing.RepaintManager.access$1200(Unknown Source)
at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
at java.awt.event.InvocationEvent.dispatch(Unknown Source)
at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
at java.awt.EventQueue.access$500(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.awt.EventQueue$3.run(Unknown Source)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(Unknown Source)
at java.awt.EventQueue.dispatchEvent(Unknown Source)
at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
at java.awt.EventDispatchThread.run(Unknown Source)