Java Calculator Program Using AWT & Applet

import java.awt.*;
import java.awt.event.*;
/*java header files required to run this program*/
import java.applet.*;

/*<applet code = "calculator.class" width = 260 height = 310></applet>*/

public class calculator extends Applet implements ActionListener
{
 TextField t1;
 Button button1,button2,button3,button4,button5,button6,button7,button8,button9,button0;
 /*All the buttons required in a Calculator Program in Java Using AWT and Applet*/
 Button add,sub,mul,div, eql, dot;
 /*Operations we are going to perform*/
 String msg="",tmp;
 int a, b;
 public void init()
 {
  setLayout(null);
  
  t1=new TextField(20);
  
  button1=new Button("1"); 
  button2=new Button("2");
  button3=new Button("3"); 
  button4=new Button("4");
  button5=new Button("5"); 
  button6=new Button("6");
  button7=new Button("7"); 
  button8=new Button("8");
  button9=new Button("9"); 
  button0=new Button("0");
  /*Initilizing a 0 to 9 number in buttons */
  
  add=new Button("+"); 
  sub=new Button("-");
  div=new Button("/"); 
  mul=new Button("*");
  dot=new Button("."); 
  eql=new Button("=");
  /*Initilizing all the operator to perform all the calculations in java AWT calculator*/
  
  add(t1); 
  /*result view window */
  
  add(button7); 
  add(button8); 
  add(button9); 
  add(div);
  /*First show in a calculator*/
  
  add(button4); 
  add(button5); 
  add(button6);
  add(mul);
  /*Second show in a calculator*/
  
  add(button1); 
  add(button2); 
  add(button3); 
  add(sub);
  /*Third show in a calculator*/
  
  add(dot); 
  add(button0); 
  add(eql);
  add(add);
  /*Forth show in a calculator*/
  
  t1.setBounds(30,30,200,40);
  button7.setBounds(30,80,44,44);
  button8.setBounds(82,80,44,44);
  button9.setBounds(134,80,44,44);
  button4.setBounds(30,132,44,44);
  button5.setBounds(82,132,44,44);
  button6.setBounds(134,132,44,44);
  button1.setBounds(30,184,44,44);
  button2.setBounds(82,184,44,44);
  button3.setBounds(134,184,44,44);
  dot.setBounds(30,236,44,44);
  button0.setBounds(82,236,44,44);
  eql.setBounds(134,236,44,44);
  add.setBounds(186,236,44,44);
  sub.setBounds(186,184,44,44);
  mul.setBounds(186,132,44,44);
  div.setBounds(186,80,44,44);
  
  button0.addActionListener(this);
  button1.addActionListener(this);
  button2.addActionListener(this);
  button3.addActionListener(this);
  button4.addActionListener(this);
  button5.addActionListener(this);
  button6.addActionListener(this);
  button7.addActionListener(this);
  button8.addActionListener(this);
  button9.addActionListener(this);
  //button0.addActionListener(this);
  //button0.addActionListener(this);
  div.addActionListener(this);
  mul.addActionListener(this);
  add.addActionListener(this);
  sub.addActionListener(this);
  eql.addActionListener(this);
 }
 public void actionPerformed(ActionEvent ae)
 {
  String str = ae.getActionCommand();
  if (str.equals("+")||str.equals("-")||str.equals("*")||str.equals("/"))
  {
   String str1 = t1.getText();
   tmp=str;
   a = Integer.parseInt(str1);
   msg="";
  }
  else if(str.equals("="))
  {
   String str2 = t1.getText();
   b = Integer.parseInt(str2);
   int sum=0;
   if(tmp=="+")
    sum=a+b;
   else if(tmp=="-")
    sum=a-b;
   else if(tmp=="*")
    sum=a*b;
   else if(tmp=="/")
    sum=a/b;
   String str1=String.valueOf(sum);
   t1.setText(""+str1);
   msg="";
  }
  else
  {
   //String ae.getActionCommand();
   //str += ae.getActionCommand();
   msg+=str;
   t1.setText(""+msg);
  }
 }
 public void paint(Graphics g)
 {
  g.setColor(Color.cyan);
  g.fillRect(20,20,220,270);
 }
}

Output: