My Programing project will not work

Question

This is the Die class, its supposed to draw a die based on the users specifications as shown in the main.

import java.awt.Color;
import java.awt.Graphics;
import javax.swing.JPanel;

public class Die extends JPanel
{
    /**
     * 
     */
    private static final long serialVersionUID = 1L;
    int xCoordinate;
    int yCoordinate;
    int num;


    Graphics pen, g;

    private static final int DIE_LENGTH = 60;        //Set's the size
    private static final int DIE_WIDTH = 60;        //of the die
    private static final int DIE_HEIGHT = 60;
    private static final int DOT_LENGTH = 10;
    private static final int DOT_WIDTH = 10;
    private static final Color LINE_COLOR = Color.black;
    private static final Color DIE_COLOR = Color.white;
    private static final Color DOT_COLOR = Color.black;
    private static final int DIE_VERT = 10;
    private static final int DIE_HORI = 10;


    public Die(int dieNum, int x, int y)
    {
        xCoordinate = x;
        yCoordinate = y;

        num = dieNum;
    }

    @Override protected void paintComponent(Graphics g)
    {
        super.paintComponent(g);
        //Creates the square
        g.drawRect(getX(), getY(), DIE_WIDTH, DIE_HEIGHT);
        g.setColor(LINE_COLOR);
        g.fillRect(xCoordinate, yCoordinate, DIE_LENGTH, DIE_WIDTH);
        if (num <= 0)
            drawBlank();
        else if (num == 1)
            drawOne();
        else if (num == 2)
            drawTwo();
        else if (num == 3)
            drawThree();
        else if (num == 4)
            drawFour();
        else if (num == 5)
            drawFive();
        else if (num == 6)
            drawSix();



    }

    private void drawBlank ()
    {
        pen.fillRect(xCoordinate, yCoordinate, DIE_LENGTH, DIE_WIDTH);
        pen.setColor(DIE_COLOR);
    }

    private void drawDot ( int x, int y)
    {
        super.paintComponent(g);
        g.setColor(DOT_COLOR);
        g.fillOval(x, y, DOT_LENGTH, DOT_WIDTH);

    }
    private void drawOne ()
    {
        super.paintComponent(g);
        drawBlank();
        drawDot(xCoordinate, yCoordinate);

    }
    private void drawTwo ()
    {
        super.paintComponent(g);
        drawBlank();
        pen.fillOval((xCoordinate - DIE_HORI), (yCoordinate + DIE_VERT), DOT_LENGTH, DOT_WIDTH);
        pen.fillOval((xCoordinate + DIE_HORI), (yCoordinate - DIE_VERT), DOT_LENGTH, DOT_WIDTH);

    }
    private void drawThree ()
    {

        drawBlank();
        drawOne();
        drawTwo();

    }

    private void drawFour ()
    {
        super.paintComponent(g);
        drawBlank();
        drawDot((xCoordinate - DIE_HORI),(yCoordinate + DIE_VERT));
        drawDot((xCoordinate + DIE_HORI),(yCoordinate + DIE_VERT));
        drawDot((xCoordinate - DIE_HORI),(yCoordinate - DIE_VERT));
        drawDot((xCoordinate + DIE_HORI),(yCoordinate - DIE_VERT));

    }

    private void drawFive ()
    {
        drawBlank();
        drawFour();
        drawOne();


    }


    private void drawSix()
    {
        drawBlank();
        drawFour();
        drawDot((xCoordinate - DIE_HORI), yCoordinate);
        drawDot((xCoordinate + DIE_HORI) , yCoordinate);

    }

}

This is the main.

import javax.swing.JFrame;
import java.awt.Color;
import java.util.Scanner;

public class RollTheDie
{

    public static void main(String[] args)
    {

        final int WINDOW_HEIGHT = 350;
        final int WINDOW_WIDTH = 300;

        System.out.println("Hi! Let's play dice!\n");

        Scanner kb = new Scanner( System.in );

        System.out.print("Enter the number on the face of the die:");
        int num = kb.nextInt();

        System.out.print("Enter the location of the die:");
        int x = kb.nextInt();
        int y = kb.nextInt();

        System.out.println("I hope you had fun! Bye!");

        JFrame dieWindow = new JFrame();
        dieWindow.setBackground(Color.gray);
        dieWindow.setSize(WINDOW_HEIGHT, WINDOW_WIDTH);
        dieWindow.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        dieWindow.setTitle("Roll the Die");

        Die newDie = new Die(num,x,y);
        dieWindow.add(newDie);
        dieWindow.setVisible(true);

        kb.close();
    }
}

When I run the code I get this null exception error which I cant seem to fix, any tips?, The errors point to the first line in my draw methods depending on what the user inputs (number of dots on the die), the Window opens but nothing is drawn and the background is white. Below is what appears in my console when I run the code

Hi! Let's play dice!

Enter the number on the face of the die:5

Enter the location of the die:50

50

I hope you had fun! Bye!

Exception in thread "AWT-EventQueue-0" java.lang.NullPointerException
    at Die.drawBlank(Die.java:67)--(This Points to the drawBlank() method first line.)
    at Die.drawFive(Die.java:115)--(This points to the drawBlank() in the method drawFive().)
    at Die.paintComponent(Die.java:57)--(This points to my paintComponent(Graphics g) method, the line that has drawFive().)
    at javax.swing.JComponent.paint(Unknown Source)
    at javax.swing.JComponent.paintChildren(Unknown Source)
    at javax.swing.JComponent.paint(Unknown Source)
    at javax.swing.JComponent.paintChildren(Unknown Source)
    at javax.swing.JComponent.paint(Unknown Source)
    at javax.swing.JLayeredPane.paint(Unknown Source)
    at javax.swing.JComponent.paintChildren(Unknown Source)
    at javax.swing.JComponent.paintToOffscreen(Unknown Source)
    at javax.swing.RepaintManager$PaintManager.paintDoubleBuffered(Unknown Source)
    at javax.swing.RepaintManager$PaintManager.paint(Unknown Source)
    at javax.swing.RepaintManager.paint(Unknown Source)
    at javax.swing.JComponent.paint(Unknown Source)
    at java.awt.GraphicsCallback$PaintCallback.run(Unknown Source)
    at sun.awt.SunGraphicsCallback.runOneComponent(Unknown Source)
    at sun.awt.SunGraphicsCallback.runComponents(Unknown Source)
    at java.awt.Container.paint(Unknown Source)
    at java.awt.Window.paint(Unknown Source)
    at javax.swing.RepaintManager$3.run(Unknown Source)
    at javax.swing.RepaintManager$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.paintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.prePaintDirtyRegions(Unknown Source)
    at javax.swing.RepaintManager.access$1100(Unknown Source)
    at javax.swing.RepaintManager$ProcessingRunnable.run(Unknown Source)
    at java.awt.event.InvocationEvent.dispatch(Unknown Source)
    at java.awt.EventQueue.dispatchEventImpl(Unknown Source)
    at java.awt.EventQueue.access$200(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.awt.EventQueue$3.run(Unknown Source)
    at java.security.AccessController.doPrivileged(Native Method)
    at java.security.ProtectionDomain$1.doIntersectionPrivilege(Unknown Source)
    at java.awt.EventQueue.dispatchEvent(Unknown Source)
    at java.awt.EventDispatchThread.pumpOneEventForFilters(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForFilter(Unknown Source)
    at java.awt.EventDispatchThread.pumpEventsForHierarchy(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.pumpEvents(Unknown Source)
    at java.awt.EventDispatchThread.run(Unknown Source)

Could you please change the title to something that describes the problem better, for the benefit of future users who search? — Dawood ibn Kareem, Mar 27 '14 at 19:55

score 2 · Answer 1 · answered Mar 27 '14 at 19:44

You declare the variable pen but never initialize it.

You have in your code:

Graphics pen, g;
// ...
private void drawBlank ()
{
    pen.fillRect(xCoordinate, yCoordinate, DIE_LENGTH, DIE_WIDTH);
    pen.setColor(DIE_COLOR);
}

But nowhere is pen actually initialized or set to an instance. When pen.fillRect() is executed, a NullPointerException will be thrown.

See @Sotirios_Delimanolis comment on your Question for more information on what a NullPointerException means.

score 0 · Answer 2 · answered Mar 27 '14 at 19:45

0

I might just be blind, but do you ever assign to g or pen?

Graphics g, pen;

EDIT: You must actually assign a Graphics object to g and pen before calling methods on them.

answered Mar 27 '14 at 19:45

Luke Joshua Park

9,527
5
27
44

My Programing project will not work

2 Answers2