Simple Calculator Using Applet

import java.applet.*; import java.awt.*; import java.awt.event.ActionEvent; import java.awt.event.ActionListener; import java.awt.event.TextEvent; import java.awt.event.TextListener;; public class calculator extends Applet implements ActionListener, TextListener { String s,s1,s2,s3,s4; Button b1,b2,b3,b4,b5,b6,b7,b8,b9,b0; Button add,sub,eq,cl,mul,div; TextField t1; int a,b,c; public void init() { t1=new TextField(10); b1=new Button("1"); b2=new Button("2"); b3=new Button("3"); b4=new Button("4"); b5=new Button("5"); b6=new Button("6"); b7=new Button("7"); b8=new Button("8"); b9=new Button("9"); b0=new Button("0"); add=new Button("+"); sub=new Button("-"); mul=new Button("*"); div=new Button("/"); eq=new Button("="); cl=new Button("Clear"); GridLayout gb=new GridLayout(4,5); setLayout(gb); add(t1); add(b1); add(b2); add(b3); add(b4); add(b5); add(b6); add(b7); add(b8); add(b9); add(b0); add(add); add(sub); add(mul); add(div); add(eq); add(cl); b1.addActionListener(this); b2.addActionListener(this); b3.addActionListener(this); b4.addActionListener(this); b5.addActionListener(this); b6.addActionListener(this); b7.addActionListener(this); b8.addActionListener(this); b9.addActionListener(this); b0.addActionListener(this); add.addActionListener(this); sub.addActionListener(this); mul.addActionListener(this); div.addActionListener(this); eq.addActionListener(this); cl.addActionListener(this); paint(); //t1.addTextListener(this); } public void paint() { setBackground(Color.green); } public void actionPerformed(ActionEvent e) { s=e.getActionCommand(); if(s.equals("0")||s.equals("1")||s.equals("2")|| s.equals("3")||s.equals("4")||s.equals("5")||s.equals("6")||s.equals("7")||s.equals("8")|| s.equals("9")||s.equals("0")) { s1=t1.getText()+s; t1.setText(s1); } if(s.equals("+")) { s2=t1.getText(); t1.setText(""); s3="+"; } if(s.equals("-")) { s2=t1.getText(); t1.setText(""); s3="-"; } if(s.equals("*")) { s2=t1.getText(); t1.setText(""); s3="*"; } if(s.equals("*")) { s2=t1.getText(); t1.setText(""); s3="*"; } if(s.equals("=")) { s4=t1.getText(); a=Integer.parseInt(s2); b=Integer.parseInt(s4); if(s3.equals("+")) c=a+b; if(s3.equals("-")) c=a-b; t1.setText(String.valueOf(c)); } if(s.equals("Clear")) { t1.setText(""); } } public void textValueChanged(TextEvent e) { } }