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我遇到了一個異常，不會暫停我的程序，真的不似乎導致任何問題，但我想知道是什麼原因導致它。從內部字符串NullPointerException異常令人困惑
在這裏，我分配SText.Text到"" + R; R是不斷地被加入到低於getWheelState()一個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;
}
}
的r值，這是我假定應該是無關緊要，如果有幫助的，爲總的鼠標滾輪滾動蜱。正向着你，負離你而去：
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;
}
}
不管怎麼說，這裏是我到目前爲止追查的方法：
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
}
}
}
這裏的堆棧跟蹤：
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)
如果它有幫助，它似乎只在我處理鼠標滾輪輸入時發生。
但它仍然讓我困惑。還有什麼可能是null如果不是g或Text？
g裏面的東西？ –
您正在捕捉異常並拋出一個新的異常，從而丟失了原始堆棧跟蹤。更好地將其改爲'拋出e;' – leonbloy
你不應該捕獲'NullPointerException'，這是一個不好的做法，在你的情況沒有理由。 – LaurentG