Swing components - event driven programming - calculator

// Swing components

// calculator

// event driven programming 

import javax.swing.*;

import java.awt.*;

import java.awt.event.*;

class calculator implements ActionListener

{

     double n1, n2, result;

     JButton b1, b2, b3, b4, b5, b6, b7, b8, b9, b0;

     JButton add,sub,mul,div,eq,dot;

     JTextField tf;

     JFrame jf;

    

     JPanel p1, p2;

    

     String s1="";

     double Num1=0;

     double Num2=0;

     double res=0;

     String opn="";

    

     calculator()

     {

          jf = new JFrame();

          jf.setSize(250,200);

          jf.setTitle("Calculator");

         

         

          tf = new JTextField("0");

          tf.setEditable(false);

          tf.setHorizontalAlignment(JTextField.RIGHT);

          jf.add(tf, BorderLayout.NORTH);

         

          GridLayout GL = new GridLayout(4,4);

          p2 = new JPanel();

          p2.setLayout(GL);

         

          b1 = new JButton("1");

          b2 = new JButton("2");

          b3 = new JButton("3");

          b4 = new JButton("4");

          b5 = new JButton("5");

          b6 = new JButton("6");

          b7 = new JButton("7");

          b8 = new JButton("8");

          b9 = new JButton("9");

          b0 = new JButton("0");

          add = new JButton("+");

          sub = new JButton("-");

          mul = new JButton("*");

          div = new JButton("/");

          eq = new JButton("=");

          dot = new JButton(".");

             

          p2.add(b9);

          p2.add(b8);

          p2.add(b7);

          p2.add(div);

          p2.add(b6);

          p2.add(b5);

          p2.add(b4);

          p2.add(mul);

          p2.add(b3);

          p2.add(b2);

          p2.add(b1);

          p2.add(sub);

          p2.add(b0);

          p2.add(dot);

          p2.add(eq);

          p2.add(add);

         

          jf.add(p2, BorderLayout.CENTER);

         

          b0.addActionListener(this);

          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);

          add.addActionListener(this);

          sub.addActionListener(this);

          mul.addActionListener(this);

          div.addActionListener(this);

          eq.addActionListener(this);

          dot.addActionListener(this);

         

          jf.setVisible(true);

          jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

     }

    

     public void actionPerformed(ActionEvent ae)

     {

          String str = ae.getActionCommand();

         

          if((str.equals("+"))||(str.equals("-"))||(str.equals("*"))||(str.equals("/")))

          {

              Num1 = Double.parseDouble(s1);

              s1="";

              tf.setText("");

              opn=str;

          }

          else if(str.equals("="))

          {

              Num2 = Double.parseDouble(s1);

              s1="";

             

              char op = opn.charAt(0);

              switch(op)

              {

                   case '+':  res = Num1+Num2;

                                  break;

                   case '-':   res = Num1-Num2;

                                  break;

                   case '*':  res = Num1*Num2;

                                  break;

                   case '/':   res = Num1/Num2;

                                  break;                                

              }

             

              tf.setText(String.valueOf(res));

          }

          else

          {

              s1=s1+str;

              tf.setText(s1);

          }

     }

    

     public static void main(String as[])

     {

          new calculator();

     }

}