java - 在 paint 方法中绘制形状

标签 java swing java-2d

我的程序是一个在JPanel上用多线程画圆的方法。以下是我的代码的一部分。我可以在 paint 方法中绘制一个 Image，但我不能在 paint 方法中绘制一个 Shape。有什么问题吗？

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;
}

错误信息:

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.

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

最佳答案

删除 Shape来自这段代码。

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

编辑:

如果声明Shape circle在构造函数中，然后是单词 circle在构造函数中表示一个名为 circle 的局部变量 (不是属性 circle)。如果您使用NetBeans 或Eclipse，您可以通过颜色来判断一个变量是局部变量还是属性。 IDE 以不同方式突出显示属性和局部变量的颜色。

关于java - 在 paint 方法中绘制形状，我们在Stack Overflow上找到一个类似的问题： https://stackoverflow.com/questions/8117251/

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