Not getting desired output while button is pressed in java applet program

//The code is as follows,i want that whatever data is there in text field T1 and T2 get subtracted and comes in T3 after we press the button...///

import java.io.*;
import java.awt.*;
import java.awt.event.*;
import  java.applet.*;
import java.awt.Font;
public class abc extends Applet implements ActionListener
{
TextField T1,T2,T3,T4,T5;
Button B1;
String ST1,ST2,ST3;
double a;
public void paint(Graphics g)
{

setLayout(null);
setBackground(Color.pink);
g.drawRect(0,0,600,500);
g.drawLine(0,50,600,50);
g.drawLine(0,80,600,80);
g.drawLine(150,50,150,80);
g.drawLine(300,50,300,80);
g.drawLine(0,110,600,110);
g.drawLine(120,80,120,150);
g.drawLine(240,80,240,150);
g.drawLine(360,80,360,150);
g.drawLine(480,80,480,150);
g.drawLine(0,150,600,150);
g.drawLine(230,150,230,360);
g.drawLine(300,150,300,170);
g.drawLine(370,150,370,170);
g.drawLine(460,150,460,390);
g.drawLine(230,170,460,170);
g.drawLine(0,390,600,390);
g.drawLine(0,360,460,360);
g.drawLine(345,200,345,390);
g.drawLine(0,200,345,200);
g.drawLine(0,420,600,420);
g.drawLine(0,220,230,220);
g.drawLine(0,240,230,240);
g.drawLine(0,260,230,260);
g.drawLine(0,280,230,280);
g.drawLine(0,300,230,300);
g.drawLine(0,320,230,320);
g.drawLine(0,340,230,340);
g.drawLine(140,220,140,360);

Label L1=new Label("A COMPANY PVT.LTD.");
L1.setBounds(150,5,440,30);
Font myFont = new Font("TimesRoman", Font.BOLD, 18);
L1.setFont(myFont);
Label L2=new Label("Ph. :01222");
L2.setBounds(200,30,250,20);
Label L3=new Label("Date ___/___/_____");
L3.setBounds(470,30,120,20);

Label L4=new Label("Vehicle No.");
Label L5=new Label("Colliery");
Label L6=new Label("Unloaded at:");
L4.setBounds(5,55,120,10);
L5.setBounds(155,55,130,15);
L6.setBounds(315,55,120,10);

this.add(L1);
this.add(L2);
this.add(L3);
this.add(L4);
this.add(L5);
this.add(L6);

Label L7=new Label("Desp.Wt.in MT");
L7.setBounds(10,84,100,25);
this.add(L7);
Label L8=new Label("Recd.Wt.in MT");
L8.setBounds(135,84,100,25);
this.add(L8);
Label L9=new Label("Shortage in MT");
L9.setBounds(255,84,100,25);
this.add(L9);
Label L10=new Label("Freight Rate PMT");
L10.setBounds(375,84,100,25);
this.add(L10);
Label L11=new Label("Advance Rs.");
L11.setBounds(500,84,95,25);
this.add(L11);

Font myFont1 = new Font("TimesRoman", Font.BOLD, 10);
Label L12=new Label("Weight  X");
L12.setBounds(240,152,55,15);
this.add(L12);
L12.setFont(myFont1);
Label L13=new Label("Freight  =");
L13.setBounds(310,152,55,15);
    this.add(L13);
L13.setFont(myFont1);
Label L14=new Label("Amount");
L14.setBounds(390,152,55,15);
this.add(L14);
L14.setFont(myFont1);


Font myFont2 = new Font("ArialBlack", Font.BOLD, 10);
Label S1=new Label("Particulars");
S1.setBounds(15,221,30,18);
S1.setFont(myFont2);
this.add(S1);
Label S2=new Label("Shortage");
S2.setBounds(5,241,30,18);
S2.setFont(myFont2);
this.add(S2);
Label S3=new Label("Advance");
S3.setBounds(5,261,30,18);
S3.setFont(myFont2);
this.add(S3);
Label S4=new Label("Commission");
S4.setBounds(5,281,30,18);
S4.setFont(myFont2);
this.add(S4);
Label S5=new Label("Munsiana");
S5.setBounds(5,301,30,18);
S5.setFont(myFont2);
this.add(S5);
Label S6=new Label("Other Deduction");
S6.setBounds(5,321,30,18);
S6.setFont(myFont2);
this.add(S6);
Label S7=new Label("Total");
S7.setBounds(5,341,30,18);
S7.setFont(myFont2);
this.add(S7);
Label R1=new Label("Amount");
R1.setBounds(150,221,40,18);
R1.setFont(myFont2);
this.add(R1);
TextField R2=new TextField();
R2.setBounds(145,241,80,18);
R2.setFont(myFont2);
this.add(R2);
TextField R3=new TextField();
R3.setBounds(145,261,80,18);
R3.setFont(myFont2);
this.add(R3);
TextField R4=new TextField();
R4.setBounds(145,281,80,18);
R4.setFont(myFont2);
this.add(R4);
TextField R5=new TextField();
R5.setBounds(145,301,80,18);
R5.setFont(myFont2);
this.add(R5);
TextField R6=new TextField();
R6.setBounds(145,321,80,18);
R6.setFont(myFont2);
this.add(R6);
TextField R7=new TextField();
R7.setBounds(145,341,80,18);
R7.setFont(myFont2);
this.add(R7);

Label L15=new Label("Total Freight Payable Rs.");
L15.setBounds(190,366,150,19);
this.add(L15);
Label L16=new Label("Rupees....................................................................................");
L16.setBounds(30,395,200,19);
this.add(L16);
Label L17=new Label("Paid Date.................................................");
L17.setBounds(10,425,200,19);
this.add(L17);
L17=new Label("Recieved By Name....................................");
L17.setBounds(10,450,200,19);
this.add(L17);
Label L18=new Label("Mobile No........................................");
L18.setBounds(10,475,200,19);
this.add(L18);
Label L19=new Label("Signature");
L19.setBounds(250,475,150,19);
this.add(L19);
Label L20=new Label("For:A Co.(P)Ltd");
L20.setBounds(440,475,155,19);
this.add(L20);

T1=new TextField();
T1.setBounds(5,118,110,28);
this.add(T1);
T2=new TextField();
T2.setBounds(125,118,110,28);
this.add(T2);
T3=new TextField();
T3.setBounds(245,118,110,28);
this.add(T3);
T4=new TextField();
T4.setBounds(365,118,110,28);
this.add(T4);
T5=new TextField();
T5.setBounds(485,118,110,28);
this.add(T5);

B1=new Button("Submit");
B1.setBounds(200,520,100,23);

B1.addActionListener(this);
this.add(B1);

T1.setText("40");
T2.setText("20");
ST1=T1.getText();
ST2=T2.getText();
a=Double.parseDouble(ST1)-Double.parseDouble(ST2);
ST3=""+a;
}

public void actionPerformed(ActionEvent ev){
Object obj=ev.getSource();
if(obj==B1)
{

System.out.println("wjnqjqw");
}
else
{
T3.setText(ST3);
System.out.println("assassas");

}
}   
}//<applet code="abc.java" width=600 height=550></applet>