NullPointerException

[chop vick]

Want my paintComponent to draw rects, ovals and lines but getting a NullPointerException. debugged my code to find which variable might be causing the problem but everything seems to be right.

Obviously not do!! Any help on this would be really appreciated!!

public class DrawPanel3 extends JPanel {

    private Random randomNumbers = new Random();
    private BorderLayout layout;
    private JLabel label;
    private JLabel label2;
    private MyShape[] shapes;
    private MyLine3 linesCnt;
    private MyOval3 ovalCnt;
    private MyRect3 rectCnt;
    private MyLine3[] lines;
    private MyRect3[] rects;
    private MyOval3[] ovals;


    //create constructor
    public DrawPanel3(Integer input) {
        super();

        //set background and border layout
        setBackground(Color.WHITE);
        layout = new BorderLayout(5, 5);
        setLayout(new BorderLayout());

        //initialize array
        MyShape[] shapes = new MyShape[3];


        //loop containing random coordinates, color and boolean
        for (int i = 0; i < input; i++) {
            int x1 = randomNumbers.nextInt(300);
            int y1 = randomNumbers.nextInt(300);
            int x2 = randomNumbers.nextInt(300);
            int y2 = randomNumbers.nextInt(300);
            Color color = new Color(randomNumbers.nextInt(256), randomNumbers.nextInt(256),
                    randomNumbers.nextInt(256));
            boolean filled = randomNumbers.nextBoolean();


            //generate random number to create different shapes
            int nextType = randomNumbers.nextInt(3);
            if (nextType == 0) {
                shapes[0] = new MyLine3(x1, x2, y1, y2, color);
                for (int lineCnt = 0; lineCnt < shapes.length; lineCnt++) {
                    shapes[lineCnt] = new MyLine3(x1, y1, x2, y2, color);
                }
            } else if (nextType == 1) {
                shapes[1] = new MyRect3(x1, x2, y1, y2, color, filled);
                for (int rectCnt = 0; rectCnt < shapes.length; rectCnt++) {
                    shapes[rectCnt] = new MyRect3(x1, y1, x2, y2, color, filled);
                }

            } else if (nextType == 2) {
                shapes[2] = new MyOval3(x1, x2, y1, y2, color, filled);
                for (int ovalCnt = 0; ovalCnt < shapes.length; ovalCnt++) {
                    shapes[ovalCnt] = new MyOval3(x1, y1, x2, y2, color, filled);
                }


            }
        }
    }


    //draw shapes
    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        for (MyShape rectangle : shapes)
            rectangle.draw(g);

        for (MyShape oval : shapes)
            oval.draw(g);

        for (MyShape line : shapes)
            line.draw(g);
    }
}

[Dave Tolls]

The stack trace for the exception will show you which line the exception is occurring on.
Can you post the stack trace here?

[chop vick]

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
	at assignment3.DrawPanel3.paintComponent(DrawPanel3.java:81)
	at javax.swing.JComponent.paint(JComponent.java:1056)
	at javax.swing.JComponent.paintChildren(JComponent.java:889)
	at javax.swing.JComponent.paint(JComponent.java:1065)
	at javax.swing.JComponent.paintChildren(JComponent.java:889)
	at javax.swing.JComponent.paint(JComponent.java:1065)
	at javax.swing.JLayeredPane.paint(JLayeredPane.java:586)
	at javax.swing.JComponent.paintChildren(JComponent.java:889)
	at javax.swing.JComponent.paintToOffscreen(JComponent.java:5217)
	at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(RepaintManager.java:1579)
	at javax.swing.RepaintManager$PaintManager.paint(RepaintManager.java:1502)
	at javax.swing.RepaintManager.paint(RepaintManager.java:1272)
	at javax.swing.JComponent.paint(JComponent.java:1042)
	at java.awt.GraphicsCallback$PaintCallback.run(GraphicsCallback.java:39)
	at sun.awt.SunGraphicsCallback.runOneComponent(SunGraphicsCallback.java:79)
	at sun.awt.SunGraphicsCallback.runComponents(SunGraphicsCallback.java:116)
	at java.awt.Container.paint(Container.java:1975)
	at java.awt.Window.paint(Window.java:3904)
	at javax.swing.RepaintManager$4.run(RepaintManager.java:842)
	at javax.swing.RepaintManager$4.run(RepaintManager.java:814)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
	at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:814)
	at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:789)
	at javax.swing.RepaintManager.prePaintDirtyRegions(RepaintManager.java:738)
	at javax.swing.RepaintManager.access$1200(RepaintManager.java:64)
	at javax.swing.RepaintManager$ProcessingRunnable.run(RepaintManager.java:1732)
	at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:311)
	at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:756)
	at java.awt.EventQueue.access$500(EventQueue.java:97)
	at java.awt.EventQueue$3.run(EventQueue.java:709)
	at java.awt.EventQueue$3.run(EventQueue.java:703)
	at java.security.AccessController.doPrivileged(Native Method)
	at java.security.ProtectionDomain$JavaSecurityAccessImpl.doIntersectionPrivilege(ProtectionDomain.java:76)
	at java.awt.EventQueue.dispatchEvent(EventQueue.java:726)
	at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:201)
	at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:116)
	at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:105)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:101)
	at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:93)
	at java.awt.EventDispatchThread.run(EventDispatchThread.java:82)

[chop vick]

line 81 is for(Myshape rectangles : shapes)
                   rectangle.draw(g);

[Moderator edit] Line 69 in the first code listing provided by OP above.

[Henry Wong]

Hint: Check your shapes instance variable. Did you ever initialize it?

[chop vick]

Ok so initialized variables and no more NullPointerException!!

But now I'm getting a blank panel.....

what should be done now?

public class DrawPanel3 extends JPanel {
    private Random randomNumbers = new Random();
    private BorderLayout layout;
    private JLabel label;
    private JLabel label2;
    private MyShape[] shapes;
    private int linesCnt = 0;
    private int ovalCnt = 0;
    private int rectCnt = 0;
    private MyLine3[] lines;
    private MyRect3[] rects;
    private MyOval3[] ovals;


    //create constructor
    public DrawPanel3(Integer input) {
        super();


        //set background and border layout
        setBackground(Color.WHITE);
        layout = new BorderLayout(5, 5);
        setLayout(new BorderLayout());

        //initialize array
        MyShape[] shapes = new MyShape[3];


        //loop containing random coordinates, color and boolean
        for (int i = 0; i < input; i++) {
            int x1 = randomNumbers.nextInt(300);
            int y1 = randomNumbers.nextInt(300);
            int x2 = randomNumbers.nextInt(300);
            int y2 = randomNumbers.nextInt(300);
            Color color = new Color(randomNumbers.nextInt(256), randomNumbers.nextInt(256),
                    randomNumbers.nextInt(256));
            boolean filled = randomNumbers.nextBoolean();


            //generate random number to create different shapes
            int nextType = randomNumbers.nextInt(3);
            if (nextType == 0) {
                shapes[0] = new MyLine3(x1, x2, y1, y2, color);
                linesCnt++;

            } else if (nextType == 1) {
                shapes[1] = new MyRect3(x1, x2, y1, y2, color, filled);
                rectCnt = 0;


            } else if (nextType == 2) {
                shapes[2] = new MyOval3(x1, x2, y1, y2, color, filled);
                ovalCnt++;

                }


            }
        }

    @Override
    //draw shapes
    public void paintComponent(Graphics g) {
        super.paintComponent(g);

        for (MyShape line : shapes)
            line.draw(g);
        for (MyShape rect : shapes)
            rect.draw(g);
        for (MyShape oval : shapes)
            oval.draw(g);


    }
}

[Norman Radder]

Also posted at: http://www.dreamincode.net/forums/topic/400540-problems-with-joptionpane/

[Tony Docherty]

Please BeForthrightWhenCrossPostingToOtherSites (← click).

We don't mind if you cross post but do tell us as we all give up our time here for free and would rather not waste it answering a question that has already been answered elsewhere.

[chop vick]

Apologies everybody, was unaware and won't be doing this again. I appreciate that everyone is helping out of there own good will and time and won't be cross posting again. Thanks for your help and time code ranchers 👍🏻

[Paul Clapham]

Well... from what you've posted it's kinda hard to tell how big your panel is when it's displayed. Perhaps its size is zero, in which case you won't see anything. (Which is your problem statement.) You can fix that by making the panel have a border and making the border be red, so you can see how big the bordered area appears.

And then there's your paintComponent method. We know it's being called because your original post mentioned an exception thrown by it. But I'd still recommend using the @Override annotation to ensure it's actually overriding JPanel's method.

And I'm not sure what that method is supposed to be doing. It looks like it's going through the shapes array and re-drawing them three times. Why the repetition?

You should also note that although you have three entries in the shapes array, there's no guarantee that all three of them will have shapes in them. Actually I'm not clear on what the purpose of the "input" parameter is when you aren't going to display more than three shapes.

[Carey Brown]

Perhaps if you had written it like this it would have been more obvious why you're getting three repetitions.

        for (MyShape shape : shapes)
            shape.draw(g);
 
        for (MyShape shape : shapes)
            shape.draw(g);
 
        for (MyShape shape : shapes)
            shape.draw(g);

[Carey Brown]

These are not being used.

    private MyLine3 linesCnt;
    private MyOval3 ovalCnt;
    private MyRect3 rectCnt;
    private MyLine3[] lines;
    private MyRect3[] rects;
    private MyOval3[] ovals;

Do you know about Lists? Seems like a better approach than your use of arrays, and with "shapes" having a fixed length of 3.

[Tony Docherty]

chop vick wrote:
But now I'm getting a blank panel.....

what should be done now?

Please can you show the code that creates and displays your panel

[Carey Brown]

            } else if (nextType == 1) {
                shapes[1] = new MyRect3(x1, x2, y1, y2, color, filled);
                for (int rectCnt = 0; rectCnt < shapes.length; rectCnt++) {
                    shapes[rectCnt] = new MyRect3(x1, y1, x2, y2, color, filled);
                }

Here you are setting shapes[1] to a new MyRect3. However, in the following loop you set shapes[0], shapes[1], and shapes[2], each to yet another new MyRect3 and each of these MyRect3 instances have exactly the same parameters.

[Edit] Sorry, seems that I missed your more recent post that does not have a loop.