Using values of two different applications that are from the same class

Question

Hi,
See the following little program
What I can't figure out is
i) How to change the values if I add a button
ii) How to print just app.x1 etc. The way I have it now, it will just print x1, y1 etc, from both app and app1, but I want to be able to distinguish between the two of them so I can use the values.....ie for example add app.x1 and app1.x2 (only using that as an example of what I want to use them for)
I'd really appreciate if anyone could help me out, it's probably simple, but just cant figure it.
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class drawLine extends JFrame{
int x1, y1, x2, y2;
JPanel topPanel;
JButton button;
public length l, l3;
public drawLine(){
super("drawLine");
public drawLine(length l){
this.l = l;
topPanel = new JPanel();
button = new JButton("Change");
topPanel.add(button);
getContentPane().add(topPanel, BorderLayout.NORTH);
x1 = 100;
y1 = 100;
x2 = l.x2;
y2 = l.y2;
System.out.println(x1 + " " + y1 + " " + x2 + " " + y2);
/*button.addActionListener(
new ActionListener(){
public void actionPerformed(ActionEvent e){
l.length();
repaint();
public void hello(){
System.out.println(x1 + " " + y1 + " " + x2 + " " + y2);
public void paint(Graphics g){
draw(g);
public void draw(Graphics g){
g.drawLine(x1, y1, x2, y2);
public static void main(String args[]){
length l1 = new length();
length l2 = (length)l1.clone();
l1.length();
l2.length();
drawLine app = new drawLine(l1);
app.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
app.setSize( 300, 300 );
app.move(0,0) ;
app.setVisible( true );
drawLine app1 = new drawLine(l2);
app1.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
app1.setSize( 300, 300 );
app1.move(300,0) ;
app1.setVisible( true );
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class length implements Cloneable{
String whatlength;
int llength;
int x1 = 100;
int y1 = 100;
public int x2, y2;
public void length(){
whatlength = JOptionPane.showInputDialog("What is the length of the line");
llength = Integer.parseInt(whatlength);
x2 = x1 + llength;
y2 = y1;
public Object clone() {
Object object = null;
try {
object = super.clone();
catch (CloneNotSupportedException exception) {
System.err.println("AbstractSpoon is not Cloneable");
return object;
}

Answer 1

I've tried it like this, ie by adding an int to drawLine and trying to keep an array of lengths, which sortof works, but see the code I have commented out in the button actionListener class. What I thought I'd ba able to do is access the arrays like that.....how come it gives me an exception?
public class drawLine extends JFrame{
int x1, y1, x2, y2;
JPanel topPanel;
JButton button;
public length[] linelength = new length[2];
public drawLine(final length l, final int k){
super("drawLine");
this.linelength[k] = l;
topPanel = new JPanel();
button = new JButton("Change");
topPanel.add(button);
getContentPane().add(topPanel, BorderLayout.NORTH);
x1 = 100;
y1 = 100;
x2 = linelength[k].x2;
y2 = linelength[k].y2;
button.addActionListener(
new ActionListener(){
public void actionPerformed(ActionEvent e){
//Update the length object int's
linelength[k].getLineLength();
// Copy these ints back to the drawline object
x2 = linelength[k].x2;
y2 = linelength[k].y2;
System.out.println(k + " " + linelength[k].x1 + " " + linelength[k].y1 + " " + linelength[k].x2 + " " + linelength[k].y2);
repaint();
/*********This bit gives me a null pointer exception ********
linelength[0].x1 = linelength[1].x1;
linelength[0].x2 = linelength[1].x2;
linelength[0].y1 = linelength[1].y1;
linelength[0].y2 = linelength[1].y2;
public void paint(Graphics g){
g.clearRect( 0, 0, getWidth(), getHeight() );
draw(g);
public void draw(Graphics g){
g.drawLine(x1, y1, x2, y2);
public static void main(String args[]){
length l1 = new length();
length l2 = (length)l1.clone();
l1.getLineLength();
l2.getLineLength();
drawLine app = new drawLine(l1, 0);
app.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
app.setSize( 300, 300 );
app.move(0,0) ;
app.setVisible( true );
drawLine app1 = new drawLine(l2, 1);
app1.setDefaultCloseOperation( JFrame.EXIT_ON_CLOSE );
app1.setSize( 300, 300 );
app1.move(300,0) ;
app1.setVisible( true );
}