Balanza En Java

como construir una balanza en java
package Capitulo10dejava;

import java.awt.Color;
import java.awt.FlowLayout;
import java.awt.Graphics;
import java.awt.GridLayout;
importjava.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.event.WindowAdapter;
import java.awt.event.WindowEvent;

import javax.swing.JButton;
import javax.swing.JFrame;
importjavax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.JTextField;

public class Balanza extends JFrame{
JLabel l1= new JLabel("+ / - peso1");
JLabel l2= new JLabel("+ / - peso2");JLabel ltot1= new JLabel();
JLabel ltot2= new JLabel();

JTextField t1 = new JTextField (5);
JTextField t2 = new JTextField (5);
JButton b1 = new JButton ( "OK");
double p1tot,p2tot;

publicstatic void main(String[] args) {
Balanza marco = new Balanza ("balanza");
WindowAdapter oye = new WindowAdapter (){
public void windowClosing (WindowEvent el ) {
System.exit (0);
}
};marco.addWindowListener(oye);
marco.setSize(600, 600);
marco.setVisible(true);
}
Balanza(String nombre){
super (nombre);
getContentPane().setLayout(new FlowLayout());
JPanel p = newJPanel( new GridLayout(3,3));
p.add(l1);
p.add(t1);
p.add(ltot1);
p.add(l2);
p.add(t2);
p.add(ltot2);
//p.add(t2);

p.add(b1);
p1tot= p2tot=0;getContentPane().add(p);

ActionListener oye = new ActionListener(){

public void actionPerformed (ActionEvent el){
String tp;
double peso1,peso2, x1,y1,x2,y2,ang;Graphics g=getGraphics();

g.setColor(Color.white);
g.fillRect(0, 150, 600, 450);
g.setColor(Color.black);
tp=t1.getText();peso1=Double.parseDouble (tp);

tp=t2.getText();
peso2=Double.parseDouble (tp);
p1tot=p1tot+peso1;
p2tot=p2tot+peso2;
ltot1.setText(""+p1tot);
ltot2.setText(""+p2tot);...