Java 在“绘制”方法中绘制形状

我的程序是一种用多线程在

JPanel

上画圆的方法。以下是我代码的一部分。我可以在paint方法中绘制

图像

，但在paint方法中无法绘制

形状

。怎么了

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;
}

错误消息： 线程“AWT-EventQueue-0”java.lang.NullPointerException中的异常 位于java.awt.geom.Path2D$Float.（Path2D.java:232） 位于java.awt.geom.Path2D$Float。（Path2D.java:207） 位于sun.java2d.pipe.BufferedRenderPipe.draw（BufferedRenderPipe.java:525） 位于sun.java2d.pipe.PixelToParallelogramConverter.draw（PixelToParallelogramConverter.java:148） 位于sun.java2d.pipe.validatePie.draw（validatePie.java:154） 位于sun.java2d.SunGraphics2D.draw（SunGraphics2D.java:2383） at tma1.Board.paint（Board.java:61） 位于javax.swing.JComponent.paintooffscreen（JComponent.java:5221） 位于javax.swing.BufferStrategyPaintManager.paint（BufferStrategyPaintManager.java:295） 位于javax.swing.RepaintManager.paint（RepaintManager.java:1206） javax.swing.JComponent.\u（JComponent.java:5169） 位于javax.swing.JComponent.paintInstance（JComponent.java:4980） 位于javax.swing.repainmanager.paintDirtyRegions（repainmanager.java:770） 位于javax.swing.repainmanager.paintDirtyRegions（repainmanager.java:728） 位于javax.swing.RepaintManager.prePaintDirtyRegions（RepaintManager.java:677） 在javax.swing.repaitmanager.access$700（repaitmanager.java:59） 在javax.swing.repaitmanager$ProcessingRunnable.run（repaitmanager.java:1621） 在java.awt.event.InvocationEvent.dispatch（InvocationEvent.java:251）中 位于java.awt.EventQueue.dispatchEventImpl（EventQueue.java:705） 在java.awt.EventQueue.access$000（EventQueue.java:101） 在java.awt.EventQueue$3.run（EventQueue.java:666） 在java.awt.EventQueue$3.run（EventQueue.java:664） 位于java.security.AccessController.doPrivileged（本机方法） 位于java.security.ProtectionDomain$1.doIntersectionPrivilege（ProtectionDomain.java:76） 位于java.awt.EventQueue.dispatchEvent（EventQueue.java:675） 位于java.awt.EventDispatchThread.pumpOneEventForFilters（EventDispatchThread.java:211） 位于java.awt.EventDispatchThread.PumpeEventsforFilter（EventDispatchThread.java:128） 位于java.awt.EventDispatchThread.PumpeEventsforHierarchy（EventDispatchThread.java:117） 位于java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:113） 位于java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:105） 在java.awt.EventDispatchThread.run（EventDispatchThread.java:90） 线程“AWT-EventQueue-0”java.lang.NullPointerException中出现异常 位于java.awt.geom.Path2D$Float.（Path2D.java:232） 位于java.awt.geom.Path2D$Float。（Path2D.java:207） 位于sun.java2d.pipe.BufferedRenderPipe.draw（BufferedRenderPipe.java:525） 位于sun.java2d.pipe.PixelToParallelogramConverter.draw（PixelToParallelogramConverter.java:148） 位于sun.java2d.pipe.validatePie.draw（validatePie.java:154） 位于sun.java2d.SunGraphics2D.draw（SunGraphics2D.java:2383） at tma1.Board.paint（Board.java:61） 位于javax.swing.JComponent.paintooffscreen（JComponent.java:5221） 位于javax.swing.BufferStrategyPaintManager.paint（BufferStrategyPaintManager.java:295） 位于javax.swing.RepaintManager.paint（RepaintManager.java:1206） javax.swing.JComponent.\u（JComponent.java:5169） 位于javax.swing.JComponent.paintInstance（JComponent.java:4980） 位于javax.swing.repainmanager.paintDirtyRegions（repainmanager.java:770） 位于javax.swing.repainmanager.paintDirtyRegions（repainmanager.java:728） 位于javax.swing.RepaintManager.prePaintDirtyRegions（RepaintManager.java:677） 在javax.swing.repaitmanager.access$700（repaitmanager.java:59） 在javax.swing.repaitmanager$ProcessingRunnable.run（repaitmanager.java:1621） 在java.awt.event.InvocationEvent.dispatch（InvocationEvent.java:251）中 位于java.awt.EventQueue.dispatchEventImpl（EventQueue.java:705） 在java.awt.EventQueue.access$000（EventQueue.java:101） 在java.awt.EventQueue$3.run（EventQueue.java:666） 在java.awt.EventQueue$3.run（EventQueue.java:664） 位于java.security.AccessController.doPrivileged（本机方法） 位于java.security.ProtectionDomain$1.doIntersectionPrivilege（ProtectionDomain.java:76） 位于java.awt.EventQueue.dispatchEvent（EventQueue.java:675） 位于java.awt.EventDispatchThread.pumpOneEventForFilters（EventDispatchThread.java:211） 位于java.awt.EventDispatchThread.PumpeEventsforFilter（EventDispatchThread.java:128） 位于java.awt.EventDispatchThread.PumpeEventsforHierarchy（EventDispatchThread.java:117） 位于java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:113） 位于java.awt.EventDispatchThread.pumpEvents（EventDispatchThread.java:105） 在java.awt.EventDispatchThread.run（EventDispatchThread.java:90） 线程“AWT-EventQueue-0”java.lang.NullPointerException中出现异常 位于java.awt.geom.Path2D$Float.（Path2D.java:232） 位于java.awt.geom.Path2D$Float。（Path2D.java:207） 位于sun.java2d.pipe.BufferedRenderPipe.draw（BufferedRenderPipe.java:525） 位于sun.java2d.pipe.PixelToParallelogramConverter.draw（PixelToParallelogramConverter.java:148） 位于sun.java2d.pipe.validatePie.draw（validatePie.java:154） 位于sun.java2d.SunGraphics2D.draw（SunGraphics2D.java:2383） at tma1.Board.paint（Board.java:61） 位于javax.swing.JComponent.paintooffscreen（JComponent.java:5221） 位于javax.swing.BufferStrategyPaintManager.paint（BufferStrategyPaintManager.java:295） 在javax.swing.RepaintManager.paint（repaitmanager.java:1206） javax.swing.JComponent.\u（JComponent.java:5169） 位于javax.swing.JComponent.paintInstance（JComponent.java:4980） 位于javax.swing.repainmanager.paintDirtyRegions（repainmanager.java:770） 位于javax.swing.repainmanager.paintDirtyRegions（repainmanager.java:728） 位于javax.swing.RepaintManager.prePaintDirtyRegions（RepaintManager.java:677） 在javax.swing.repainmanager。

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.

................

public Star(int delay,int initialX,int initialY){
    Shape circle = new Ellipse2D.Float(initialX,initialY,100f,100f);