Struggling to find source of error 1

[raptor1]

Hi, I having been struggling to find the ClassCastException Error in the following code which is designed to display a digital number depending on the number entered into the option pane:

import java.applet.Applet;
import javax.swing.JOptionPane;
import java.awt.*;
import java.awt.event.*;


public class AssignmentTask2 {
	private SDisplay display;


public void init() {

	SDisplay display = new SDisplay(100, 100, 10, 50);

	display.startDisplay();

}

public void paint (Graphics g) {

	display.drawNumber(g);
}
}

class SDisplay extends Applet{

	int num;
	int segmentW;
	int segmentL;
	int Coord [][];
	String Number; 	          // The number entered by the user
	int Segments;	          // The number after conversion from string to integer
        boolean SegmentStatus;

public SDisplay(int width, int length, int x, int y){

	this.segmentW = width;
	this.segmentL = length;
	this.Coord = new int [2] [7];
	this.Coord[0][0] = segmentW + x;
	this.Coord[1][0] = 0 + y;
	this.Coord[0][1] = segmentW + segmentL + x;
	this.Coord[1][1] = segmentW + y;
	this.Coord[0][2] = Coord[0][1];
	this.Coord[1][2] = Coord[1][1] + segmentW + segmentL;
	this.Coord[0][3] = segmentW + x;
	this.Coord[1][3] = (segmentW + segmentL)*2 + y;
	this.Coord[0][4] = 0 + x;
	this.Coord[1][4] = Coord[1][2];
	this.Coord[0][5] = 0 + x;
	this.Coord[1][5] = segmentW + y;
	this.Coord[0][6] = Coord[0][5] + segmentW;
	this.Coord[1][6] = Coord[1][5] + segmentL;
        //this.num = numbers;
}

public void startDisplay(){

	// Read the number from the user

	Number = JOptionPane.showInputDialog (null, "Enter a number between 0 - 9");

	// Convert the string to an integer value

	Segments = Integer.parseInt(Number);
}

public boolean Segment ( int choice, int segmentId ) {

	boolean segmentStatus = false;

	switch (segmentId) {

	case 0 : if ((choice == 0) | (choice == 2) | (choice == 3) | (choice == 5) | (choice == 6)| (choice == 7) | (choice == 8) |
		     (choice == 9)) SegmentStatus = true;
		 else SegmentStatus = false;
		 break;
	case 1 : if ((choice == 0) | (choice == 1) | (choice == 2) | (choice == 3) | (choice == 4)| (choice == 7) | (choice == 8) |
		     (choice == 9)) SegmentStatus = true;
		 else SegmentStatus = false;
		 break;
	case 2 : if ((choice == 0) | (choice == 1) | (choice == 3) | (choice == 4) | (choice == 5)| (choice == 6) | (choice == 7) |
		     (choice == 8) | (choice == 9)) SegmentStatus = true;
		 else SegmentStatus = false;
		 break;
	case 3 : if ((choice == 0) | (choice == 2) | (choice == 3) | (choice == 5) | (choice == 6)| (choice == 8) | (choice == 9)) 		 		 SegmentStatus = true;
		 else SegmentStatus = false;
		 break;
	case 4 : if ((choice == 0) | (choice == 2) | (choice == 6) | (choice == 8))
		 segmentStatus = true;
		 else segmentStatus = false;
		 break;
	case 5 : if ((choice == 0) | (choice == 4) | (choice == 5) | (choice == 6) | (choice == 8)| (choice == 9))
		 segmentStatus = true;
		 else segmentStatus = false;
		 break;
	case 6 : if ((choice == 2) | (choice == 3) | (choice == 4) | (choice == 5) | (choice == 6)| (choice == 8) | (choice == 9))
		 segmentStatus = true;
		 else segmentStatus = false;
		 break;
	}

	return segmentStatus;
}

private void FilledRectangle ( int choice, boolean Seg, Graphics g){

	g.setColor(Color.red);

	if (Seg) {
		g.fillRect(this.Coord[0][choice], this.Coord[0][choice], this.segmentW, this.segmentL);}
	else{
		g.drawRect(this.Coord[0][choice], this.Coord[0][choice], this.segmentW, this.segmentL);
	}
}

private void drawEmpty(int a, boolean v, Graphics g){

        g.setColor(Color.white);

	if (v)
            g.fillRect(this.Coord[0][a], this.Coord[1][a], this.segmentW, this.segmentL);
        else
            g.fillRect(this.Coord[0][a], this.Coord[1][a], this.segmentL, this.segmentW);

}

private void drawSeg (int segments, boolean status, Graphics g){

			if ((status) & ((segments == 1) | (segments == 2) | (segments == 4) | (segments == 5))){
			boolean  t = true;
			FilledRectangle(segments, t, g);
			}
		else if ((status) & ((segments == 0) | (segments == 3) | (segments == 6))){
			boolean t = false;
			FilledRectangle(segments, t, g);
			}
		else if ((!status) & ((segments == 1) | (segments == 2) | (segments == 4) | (segments == 5))){
			boolean t = true;
			drawEmpty(segments, t, g);
			}
		else if ((!status) & ((segments == 0) | (segments == 3) | (segments == 6))){
			boolean t = false;
			drawEmpty(segments, t, g);
			}
}


public void drawNumber(Graphics g) {

	for (int Segments=0; Segments<=6;Segments++){
		boolean state = Segment(this.num, Segments);
		drawSeg ( Segments, state, g);
	}
}
}

 

[wushutwist]

There is actually a simple answer to your problem. Your class AssignmentTask2 needs to extend from Applet.

 

[raptor1]

Thanks for the help wushutwist,

As you can probably tell im rather new to programming in java.

Now its cleared up the ClassCastException error but now theres a null pointer exception occuring.

 

[wushutwist]

This is another small error in your code. Very common for beginners. In AssignmentTask2.init you are overshadowing your SDisplay object, thus when you attempt to use it in AssignmentTask2.paint a NullPointerException is thrown.

Your code:

public void init() {
  SDisplay display = new SDisplay(100, 100, 10, 50);
  display.startDisplay();
}

Correct code:

public void init() {
  display = new SDisplay(100, 100, 10, 50);
  display.startDisplay();
}

Do you see the subtle, but oh so important, difference? Programming is all about the small details.

Disclaimer: This is probably not your only problem.

 

[ACRRHODES]

Makes sense. Hmm... I'd better keep that in mind myself.

Note, raptor1, that another similar cause of [tt]NullPointerException[/tt]s is the following:

Incorrect Code:
[tt]
public class DoesntReallyMatter
{
Image buffer = new Image();

public void paint(Graphics g)
{
buffer.drawSomething(...);
}
}
[/tt]

Correct Code:
[tt]
public class DoesntReallyMatter
{
Image buffer = createImage(...);

public void paint(Graphics g)
{
buffer.drawSomething(...);
}
}
[/tt]

As you can see, some types variables have to have content before they can be used, such as draw-on-it able images. That is, only Images that have been [tt]create[/tt]d can be drawn on. Otherwise the Image can only serve as a pointer to an image file. ***
Dammit Jim, I'm a programmer, not a doctor.