我遇到了一个异常，它不会停止我的程序，并且似乎似乎导致任何问题，但我想知道导致它的原因。
在此，我将SText.Text分配给"" + R; R是一个不断添加到getWheelState()下面的int：
SText ST = new SText("",Mainfont,Color.orange,10,300);
Window.addEntity(ST);//Adds ST to a list of things to draw.
int R = 0;
while(true)
{
int C = SIn.getWheelState(); //static method that calls (Some MouseWheelEvent).getWheelRotation()
ST.Text = ""+R; //Changing Text here
if(R+C != R)
{
R += C;
}
}
R的值，我假设应该是无关紧要的，如果有用的话，是鼠标滚轮的总滚动滴答。对你不利，对你不利：
public class SInput extends MouseAdapter implements MouseListener, MouseWheelListener, KeyListener
{
protected int MouseScrolled = 0;
public void mouseWheelMoved(MouseWheelEvent e)
{
MouseScrolled += e.getWheelRotation();
}
public int HandleWheel()
{
int temp = MouseScrolled;
MouseScrolled = 0;
return temp;
}
}
无论如何，这是我到目前为止所追踪的方法：
public class SText extends SEntity
{
public String Text; public Color Col; public Font Fnt;
public SText(String text,Font f,Color cl,int a,int b)
{
Fnt = f;
Text = text;
Col = cl;
x = a;
y = b;
}
public void draw(Graphics g)
{
try
{
g.drawString(Text,x,y); // Line in question
}
catch(NullPointerException e)
{
if(Text != null && g != null)
throw e; //Exception gets thrown anyways
}
}
}
这是堆栈跟踪：
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.lang.String.length(String.java:623)
at sun.font.GlyphList.setFromString(GlyphList.java:241)
at sun.java2d.pipe.GlyphListPipe.drawString(GlyphListPipe.java:71)
at sun.java2d.SunGraphics2D.drawString(SunGraphics2D.java:2829)
at SebsGameEngine.SText.draw(SText.java:29)
at SebsGameEngine.SPanel.paintComponent(SPanel.java:37)
at javax.swing.JComponent.paint(JComponent.java:1054)
at javax.swing.JComponent.paintChildren(JComponent.java:887)
at javax.swing.JComponent.paint(JComponent.java:1063)
at javax.swing.JComponent.paintChildren(JComponent.java:887)
at javax.swing.JComponent.paint(JComponent.java:1063)
at javax.swing.JLayeredPane.paint(JLayeredPane.java:585)
at javax.swing.JComponent.paintChildren(JComponent.java:887)
at javax.swing.JComponent.paintToOffscreen(JComponent.java:5228)
at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:295)
at javax.swing.RepaintManager.paint(RepaintManager.java:1236)
at javax.swing.JComponent.paint(JComponent.java:1040)
at java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:39)
at sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:78)
at sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:115)
at java.awt.Container.paint(Container.java:1967)
at java.awt.Window.paint(Window.java:3877)
at javax.swing.RepaintManager$3.run(RepaintManager.java:807)
at javax.swing.RepaintManager$3.run(RepaintManager.java:784)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:784)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:757)
at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:706)
at javax.swing.RepaintManager.access$1000(RepaintManager.java:62)
at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1647)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:733)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:694)
at java.awt.EventQueue$3.run(EventQueue.java:692)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:703)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:242)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:161)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:150)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:146)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:138)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:91)
如果它有所帮助，那么只有当我处理鼠标滚轮输入时才会发生这种情况。
但它仍然让我感到困惑。如果不是null或g， 可以<{1}}还有什么？
答案 0 :(得分：0)
要发现Text为null的原因，您应该向我们展示实例化SText类的代码段，因为您使用在SText类中创建对象的代码段中设置的文本和文本值来初始化SText。请把你的代码放在这里。当然Text或g是null，因为我们在SebsGameEngine.SText.draw（SText.java:29）并且它在draw方法中显示空指针存在。