Java绘图类不显示矩形数组

时间:2015-04-22 23:25:06

标签: java swing

我试图打印一个矩形数组并在运行时遇到错误。

我从我的主类中发送一个数字,只是一个普通的int,例如5,在我的paint类中的getdatafordisplay(the number I send)函数。这在if语句中进行了一些检查,因此我们知道在哪里显示矩形。到目前为止,这在我的程序中运行良好。

现在它将它保存在矩形类中,然后应该在运行时显示所有矩形?

另外值得一提的是,我从这个网站上了解到用户在这里发布的主动方法:https://tips4java.wordpress.com/2009/05/08/custom-painting-approaches/

我的涂料类是:

class mainPanel extends JPanel
{
    int processes, storedProcesses;

    //for inital values of rectangles
    int xCoor = 0;
    int yCoor = 0;
    int width = 10;
    int height = 50;

    static int x = 100;
    int [] y = {100,150,200,250,300,350,400,450,500,550};

    private ArrayList<ColoredRectangle> coloredRectangles = new ArrayList<ColoredRectangle>();

    class ColoredRectangle
    {
          private Rectangle rectangle;

          public ColoredRectangle()
          {
                 System.out.println("REC");
          }

        public Rectangle getRectangle()
        {
              return rectangle;
        }
    }

    public void addRectangle(ColoredRectangle rectangle)
    {
          coloredRectangles.add( rectangle );
          repaint();
    }

    public mainPanel(int processFROMmain)
    {
        //just some jpanel looks here
    }

    public Dimension getPreferredSize() {
        return new Dimension (1000, 1000);
    }

    public void getDataForDisplay (int proc)
    {
    //the method checks the value from "proc" to see where to display a rectangle on screen. proc comes from user i.e 5
    int loop = 0;

    while (loop < storedProcesses)
    {
        int breakloop = 0;

        if (proc == loop)
        {
            xCoor =  x;
            yCoor = y[loop];
            x = x + 10;
            breakloop = 1;
            Rectangle r = new Rectangle(xCoor, yCoor, width, height);
            ColoredRectangle cr = new ColoredRectangle();
            addRectangle( cr );
        }

        if (breakloop == 1)
        {
            break;
        }

        loop++;
    }
 }

  public void paintComponent(Graphics g) {
       super.paintComponent(g);   

    for (mainPanel.ColoredRectangle cr : coloredRectangles)
        {
        g.setColor(Color.RED );
        Rectangle r = cr.getRectangle();
        g.drawRect(r.x, r.y, r.width, r.height);
        }
    }  
}

我得到的错误是:

  

线程中的异常&#34; AWT-EventQueue-0&#34;显示java.lang.NullPointerException
  在mainPanel.paintComponent(main.java:275)
  在javax.swing.JComponent.paint(JComponent.java:1045)
          在javax.swing.JComponent.paintChildren(JComponent.java:878)           在javax.swing.JComponent.paint(JComponent.java:1054)           在javax.swing.JComponent.paintChildren(JComponent.java:878)           在javax.swing.JComponent.paint(JComponent.java:1054)           在javax.swing.JLayeredPane.paint(JLayeredPane.java:585)           在javax.swing.JComponent.paintChildren(JComponent.java:878)           在javax.swing.JComponent.paintToOffscreen(JComponent.java:5217)           在javax.swing.BufferStrategyPaintManager.paint(BufferStrategyPaintManager.java:295)           在javax.swing.RepaintManager.paint(RepaintManager.java:1249)           在javax.swing.JComponent.paint(JComponent.java:1031)           在java.awt.GraphicsCallback $ PaintCallback.run(GraphicsCallback.java:39)           at sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:78)           at sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:115)           在java.awt.Container.paint(Container.java:1967)           在java.awt.Window.paint(Window.java:3877)           在javax.swing.RepaintManager $ 3.run(RepaintManager.java:819)           在javax.swing.RepaintManager $ 3.run(RepaintManager.java:796)           at java.security.AccessController.doPrivileged(Native Method)           at java.security.ProtectionDomain $ 1.doIntersectionPrivilege(ProtectionDomain.java:76)           在javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:796)           在javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:769)           在javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:718)           在javax.swing.RepaintManager.access $ 1100(RepaintManager.java:62)           在javax.swing.RepaintManager $ ProcessingRunnable.run(RepaintManager.java:1677)           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)

2 个答案:

答案 0 :(得分:4)

您永远不会在Rectangle个对象中存储ColoredRectangle个对象。您正在初始化变量private Rectangle rectangle;,但这就是它。你应该编辑你的代码。

private Rectangle rectangle;

    public ColoredRectangle(Rectangle rectangle) {
        this.rectangle = rectangle;
        System.out.println("REC");
}

getDataForDisplay方法中;

Rectangle r = new Rectangle(xCoor, yCoor, width, height);
ColoredRectangle cr = new ColoredRectangle(r);

答案 1 :(得分:1)

当您尝试访问矩形属性之一时,忘记将RectangleColoredRectange连接为NPE。

(快速和肮脏)修复将是:

Rectangle r = new Rectangle(xCoor, yCoor, width, height);
ColoredRectangle cr = new ColoredRectangle();
cr.rectangle = r; //<-- adding this line
addRectangle( cr );