[英]Draw a Shape within paint method
My program is a method to draw a circle on JPanel
with multi-thread. 我的程序是使用多线程在
JPanel
上画圆的方法。 The following is a part of my code. 以下是我的代码的一部分。 I can draw a
Image
in the paint method, but I can't draw a Shape
in paint method. 我可以使用绘制方法绘制
Image
,但不能使用绘制方法绘制Shape
。 What's wrong with it? 它出什么问题了?
public void paint(Graphics g) {
if (draw == true) {
super.paint(g);
Graphics2D g2d = (Graphics2D)g;
for (Star s : this.items) {
g2d.draw(s.cirle);
}
Toolkit.getDefaultToolkit().sync();
g.dispose();
}
}
// a constructor of my star class
public Star(int delay,int initialX,int initialY){
//ImageIcon ii = new ImageIcon(this.getClass().getResource("star.jpg"));
//starImage = ii.getImage();
Shape circle = new Ellipse2D.Float(initialX,initialY,100f,100f);
System.out.println(circle);
x=initialX;
y=initialY;
randomDesXY();
this.delay=delay;
}
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.awt.geom.Path2D$Float.<init>(Path2D.java:232)
at java.awt.geom.Path2D$Float.<init>(Path2D.java:207)
at sun.java2d.pipe.BufferedRenderPipe.draw(BufferedRenderPipe.java:525)
at sun.java2d.pipe.PixelToParallelogramConverter.draw(PixelToParallelogramConverter.java:148)
at sun.java2d.pipe.ValidatePipe.draw(ValidatePipe.java:154)
at sun.java2d.SunGraphics2D.draw(SunGraphics2D.java:2383)
at tma1.Board.paint(Board.java:61)
at javax.swing.JComponent.paintToOffscreen(JComponent.java:5221)
at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:295)
at javax.swing.RepaintManager.paint(RepaintManager.java:1206)
at javax.swing.JComponent._paintImmediately(JComponent.java:5169)
at javax.swing.JComponent.paintImmediately(JComponent.java:4980)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:770)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:728)
at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:677)
at javax.swing.RepaintManager.access$700(RepaintManager.java:59)
at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1621)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:675)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.awt.geom.Path2D$Float.<init>(Path2D.java:232)
at java.awt.geom.Path2D$Float.<init>(Path2D.java:207)
at sun.java2d.pipe.BufferedRenderPipe.draw(BufferedRenderPipe.java:525)
at sun.java2d.pipe.PixelToParallelogramConverter.draw(PixelToParallelogramConverter.java:148)
at sun.java2d.pipe.ValidatePipe.draw(ValidatePipe.java:154)
at sun.java2d.SunGraphics2D.draw(SunGraphics2D.java:2383)
at tma1.Board.paint(Board.java:61)
at javax.swing.JComponent.paintToOffscreen(JComponent.java:5221)
at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:295)
at javax.swing.RepaintManager.paint(RepaintManager.java:1206)
at javax.swing.JComponent._paintImmediately(JComponent.java:5169)
at javax.swing.JComponent.paintImmediately(JComponent.java:4980)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:770)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:728)
at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:677)
at javax.swing.RepaintManager.access$700(RepaintManager.java:59)
at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1621)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:675)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.awt.geom.Path2D$Float.<init>(Path2D.java:232)
at java.awt.geom.Path2D$Float.<init>(Path2D.java:207)
at sun.java2d.pipe.BufferedRenderPipe.draw(BufferedRenderPipe.java:525)
at sun.java2d.pipe.PixelToParallelogramConverter.draw(PixelToParallelogramConverter.java:148)
at sun.java2d.pipe.ValidatePipe.draw(ValidatePipe.java:154)
at sun.java2d.SunGraphics2D.draw(SunGraphics2D.java:2383)
at tma1.Board.paint(Board.java:61)
at javax.swing.JComponent.paintToOffscreen(JComponent.java:5221)
at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:295)
at javax.swing.RepaintManager.paint(RepaintManager.java:1206)
at javax.swing.JComponent._paintImmediately(JComponent.java:5169)
at javax.swing.JComponent.paintImmediately(JComponent.java:4980)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:770)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:728)
at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:677)
at javax.swing.RepaintManager.access$700(RepaintManager.java:59)
at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1621)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:675)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.awt.geom.Path2D$Float.<init>(Path2D.java:232)
at java.awt.geom.Path2D$Float.<init>(Path2D.java:207)
at sun.java2d.pipe.BufferedRenderPipe.draw(BufferedRenderPipe.java:525)
at sun.java2d.pipe.PixelToParallelogramConverter.draw(PixelToParallelogramConverter.java:148)
at sun.java2d.pipe.ValidatePipe.draw(ValidatePipe.java:154)
at sun.java2d.SunGraphics2D.draw(SunGraphics2D.java:2383)
at tma1.Board.paint(Board.java:61)
at javax.swing.JComponent.paintToOffscreen(JComponent.java:5221)
at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:295)
at javax.swing.RepaintManager.paint(RepaintManager.java:1206)
at javax.swing.JComponent._paintImmediately(JComponent.java:5169)
at javax.swing.JComponent.paintImmediately(JComponent.java:4980)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:770)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:728)
at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:677)
at javax.swing.RepaintManager.access$700(RepaintManager.java:59)
at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1621)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:675)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:113)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:105)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:90)
Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at java.awt.geom.Path2D$Float.<init>(Path2D.java:232)
at java.awt.geom.Path2D$Float.<init>(Path2D.java:207)
at sun.java2d.pipe.BufferedRenderPipe.draw(BufferedRenderPipe.java:525)
at sun.java2d.pipe.PixelToParallelogramConverter.draw(PixelToParallelogramConverter.java:148)
at sun.java2d.pipe.ValidatePipe.draw(ValidatePipe.java:154)
at sun.java2d.SunGraphics2D.draw(SunGraphics2D.java:2383)
at tma1.Board.paint(Board.java:61)
at javax.swing.JComponent.paintToOffscreen(JComponent.java:5221)
at javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:295)
at javax.swing.RepaintManager.paint(RepaintManager.java:1206)
at javax.swing.JComponent._paintImmediately(JComponent.java:5169)
at javax.swing.JComponent.paintImmediately(JComponent.java:4980)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:770)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:728)
at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:677)
at javax.swing.RepaintManager.access$700(RepaintManager.java:59)
at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1621)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:251)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:705)
at java.awt.EventQueue.access$000(EventQueue.java:101)
at java.awt.EventQueue$3.run(EventQueue.java:666)
at java.awt.EventQueue$3.run(EventQueue.java:664)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:675)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:211)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:128)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:117)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.
................
paintComponent()
method, not the paint()
method. paintComponent()
方法中完成,而不是在paint()
方法中完成。 dispose()
method on the Graphics
object. Graphics
对象上使用dispose()
方法。 The only time you use dispose()
is when you create your own Graphics
object. dispose()
是在创建自己的Graphics
对象时。 sync()
method. sync()
方法。 I've never seen that in painting code before. Remove Shape
from this code. 从此代码中删除
Shape
。
public Star(int delay,int initialX,int initialY){
Shape circle = new Ellipse2D.Float(initialX,initialY,100f,100f);
Edit: 编辑:
If you declare Shape circle
in the constructor, then the word circle
in the constructor means a local variable named circle
(not an attribute circle
). 如果在构造函数中声明
Shape circle
,则构造函数中的单词circle
表示一个名为circle
的局部变量 (不是attribute circle
)。 If you use NetBeans or Eclipse, you can check whether a variable is a local variable or an attribute by its color. 如果使用NetBeans或Eclipse,则可以按颜色检查变量是局部变量还是属性。 The IDE highlights the color of attributes and local variables differently.
IDE突出显示属性和局部变量的颜色。
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