NullPointerException in passing value to a class file

Question

I am making a Java program which allows a user to draw a selected geometric object.

I would like to know what particular block/s of code produces this error when I press the Draw Button.

This code snippet will basically receive the values inputted from the user and will pass it to either one of four classes which is used for drawing the shape/object.

EDIT: Here is the full actionPerforemed class

   public void actionPerformed (ActionEvent e)
    {
    if (e.getSource() == exitButton)
    {
        System.exit(0);
    }

    if (e.getSource() == clearButton)
    {
        field1.setText("");
        field2.setText("");
        field3.setText("");
        field4.setText("");
        field5.setText("");
        field6.setText("");
        field7.setText("");
        field8.setText("");


        clearButton.setEnabled(false);
        drawButton.setEnabled(false);
    }

    if (e.getSource() == drawButton)
    {
        if (combo.getSelectedIndex() == 1)
        {
            x1 = Integer.parseInt(field1.getText());
            y1 = Integer.parseInt(field4.getText());

            Dot.paintPoint(g, x1, y1);
        }

        if (combo.getSelectedIndex() == 2)
        {
            x1 = Integer.parseInt(field1.getText());
            y1 = Integer.parseInt(field4.getText());
            x2 = Integer.parseInt(field2.getText());
            y2 = Integer.parseInt(field5.getText());


            Line.paintLine(g,x1,y1,x2,y2);
        }

        if (combo.getSelectedIndex() == 3)
        {
            x1 = Integer.parseInt(field1.getText());
            y1 = Integer.parseInt(field4.getText());
            w = Integer.parseInt(field7.getText());
            h = Integer.parseInt(field8.getText());

            Oval.paintOval(g,x1,y1,w,h);
        }

        if (combo.getSelectedIndex() == 4)
        {
            x1 = Integer.parseInt(field1.getText());
            y1 = Integer.parseInt(field4.getText());
            x2 = Integer.parseInt(field2.getText());
            y2 = Integer.parseInt(field5.getText());
            x3 = Integer.parseInt(field3.getText());
            y3 = Integer.parseInt(field6.getText());

            Traingle.paintTriangle(g,x1,y1,x2,y2,x3,y3);
        }
    }
}

Here are the four classes.

For Making a Point:

import java.awt.*;

public class Dot
{
protected static int x1,y1;


public Dot()
{
    setPoint(0,0);
}

public Dot(int x1, int y1)
{
    setPoint(x1,y1);
}

public void setPoint(int x1, int y1)
{
    this.x1 = x1;
    this.y1 = y1;
}

public static int getX1()
{
    return x1;
}

public static int getY1()
{
    return y1;
}

public static void paintPoint(Graphics g, int x1, int y1)
{
    g.drawString(".", x1,y1);
}

}

For Making a Line:

import java.awt.*;

public class Line extends Dot
{
protected static int x2,y2;


public Line()
{
    setPoint(0,0,0,0);
}

public Line(int x1, int y1, int x2, int y2)
{
    setPoint(x1,y1,x2,y2);
}

public void setPoint(int x1, int y1, int x2, int y2)
{
    this.x1 = x1;
    this.y1 = y1;
    this.x2 = x2;
    this.y2 = y2;
}

public static int getX2()
{
    return x2;
}

public static int getY2()
{
    return y2;
}

public static void paintLine(Graphics g, int x1, int y1, int x2, int y2)
{
    g.drawLine(x1,y1,x2,y2);
}



}

For Making an Oval:

import java.awt.*;

public class Oval extends Dot
{
protected static int w,h;


public Oval()
{
    super(0,0);
}

public Oval(int x1, int y1)
{
    super(x1,y1);

}

public void setPoint(int x1, int y1)
{
    this.x1 = x1;
    this.y1 = y1;
    this.w = w;
    this.h = h;
}


public static int getWidth()
{
    return w;
}

public static int getHeight()
{
    return h;
}

public static void paintOval(Graphics g, int x1,int y1, int w, int h)
{
    g.drawOval(x1,y1,w,h);
}



}

And for making a Triangle:

import java.awt.*;

public class Traingle extends Line
{
protected static int x3,y3;


public Traingle()
{
    setPoint(0,0,0,0,0,0);
}

public Traingle(int x1, int y1, int x2, int y2)
{
    setPoint(x1,y1,x2,y2,x3,y3);
}

public void setPoint(int x1, int y1, int x2, int y2,int x3, int y3)
{
    this.x1 = x1;
    this.y1 = y1;
    this.x2 = x2;
    this.y2 = y2;
    this.x3 = x3;
    this.y3 = y3;
}

public static int getX3()
{
    return x3;
}

public static int getY3()
{
    return y3;
}

public static void paintTriangle(Graphics g, int x1, int y1, int x2, int y2, int x3, int y3)
{
    g.drawLine(x1,y1,x2,y2);
    g.drawLine(x2,y2,x3,y3);
    g.drawLine(x1,y1,x3,y3);
}



}

And the error goes like this:

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
at Dot.paintPoint(Dot.java:36)
at ShapeDriver.actionPerformed(ShapeDriver.java:451)
at javax.swing.AbstractButton.fireActionPerformed(AbstractButton.java:2018)
at javax.swing.AbstractButton$Handler.actionPerformed(AbstractButton.java:2341)
at javax.swing.DefaultButtonModel.fireActionPerformed(DefaultButtonModel.java:402)
at javax.swing.DefaultButtonModel.setPressed(DefaultButtonModel.java:259)
at javax.swing.plaf.basic.BasicButtonListener.mouseReleased(BasicButtonListener.java:252)
at java.awt.Component.processMouseEvent(Component.java:6505)
at javax.swing.JComponent.processMouseEvent(JComponent.java:3321)
at java.awt.Component.processEvent(Component.java:6270)
at java.awt.Container.processEvent(Container.java:2229)
at java.awt.Component.dispatchEventImpl(Component.java:4861)
at java.awt.Container.dispatchEventImpl(Container.java:2287)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.LightweightDispatcher.retargetMouseEvent(Container.java:4832)
at java.awt.LightweightDispatcher.processMouseEvent(Container.java:4492)
at java.awt.LightweightDispatcher.dispatchEvent(Container.java:4422)
at java.awt.Container.dispatchEventImpl(Container.java:2273)
at java.awt.Window.dispatchEventImpl(Window.java:2719)
at java.awt.Component.dispatchEvent(Component.java:4687)
at java.awt.EventQueue.dispatchEventImpl(EventQueue.java:723)
at java.awt.EventQueue.access$200(EventQueue.java:103)
at java.awt.EventQueue$3.run(EventQueue.java:682)
at java.awt.EventQueue$3.run(EventQueue.java:680)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:87)
at java.awt.EventQueue$4.run(EventQueue.java:696)
at java.awt.EventQueue$4.run(EventQueue.java:694)
at java.security.AccessController.doPrivileged(Native Method)
at java.security.ProtectionDomain$1.doIntersectionPrivilege(ProtectionDomain.java:76)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:693)
at java.awt.EventDispatchThread.pumpOneEventForFilters(EventDispatchThread.java:244)
at java.awt.EventDispatchThread.pumpEventsForFilter(EventDispatchThread.java:163)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:147)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:139)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:97)

Any help would be appreciated. Thanks in advance.

Show us the `actionPerformed` method of class `ShapeDriver`. — Sotirios Delimanolis, Sep 29 '13 at 13:55
Ok so where does your `Graphics` object `g` come from in the `ShapeDriver` class? — Sotirios Delimanolis, Sep 29 '13 at 13:59
@SotiriosDelimanolis I declared it together with my object declaration of the interger variables. It goes like this: `Graphics g` — terrible-coder, Sep 29 '13 at 14:03
Yes, I haven't initialized the `Graphics` object. For now, I will try it to see the results. Thank you for your suggestion. — terrible-coder, Sep 29 '13 at 14:10
If you haven't initialized it, then it will remain `null` and give you `NullPointerExceptions` left and right. — Sotirios Delimanolis, Sep 29 '13 at 14:12
@Sotirios Delimanolis I can't seem to initialize Graphics. How can I do it? — terrible-coder, Sep 29 '13 at 20:31

score 0 · Answer 1 · edited May 23 '17 at 10:32

0

There's not enough code to say for sure, but I reckon your Graphics object is null (the g you are passing into the paint methods).

Now, more importantly, this code is bad. You are using statics for your variables. I suggest you read this Java Static vs Instance

edited May 23 '17 at 10:32

Community

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answered Sep 29 '13 at 13:57

sksamuel

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NullPointerException in passing value to a class file

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