application of Calculator using Applet.

Aim: Write an application of Calculator using Applet.

package bc;

import java.awt.*;

import java.awt.event.*;

import java.applet.*;

public class calc extends Applet implements ActionListener

{

Button keysArray[];

Panel keyPad;

TextField Field;

double result;

boolean first;

static boolean clearText;

int prevOpe;

public void init()

{

Field = new TextField(20);

keyPad = new Panel ();

keysArray = new Button[17];

result = 0.0;

prevOpe = 0;

first = true;

clearText = true;

//Create buttons

for (int i = 0; i <=9; i++)

keysArray[i] = new Button(String.valueOf(i));

keysArray[10] = new Button("/");

keysArray[11] = new Button("*");

keysArray[12] = new Button("-");

keysArray[13] = new Button("+");

keysArray[14] = new Button("=");

keysArray[15] = new Button(".");

keysArray[16] = new Button("CLR");

//Set panel layout manager

keyPad.setLayout(new GridLayout (4,4));

//Add button to keyPad panel

for (int i = 7; i <=10; i++) //adds Button 7,8,9, and divide to Panel

keyPad.add(keysArray[i]);

for (int i = 4; i <=6; i++)

keyPad.add(keysArray[i]);

keyPad.add(keysArray[11]);

for (int i = 1; i <= 3;i++)

keyPad.add(keysArray[i]);

keyPad.add(keysArray[12]);

keyPad.add(keysArray[0]);

for (int i = 15; i >=13; i--)

keyPad.add(keysArray[i]); //adds decimal point, equal, and add keys Panel

add(Field, BorderLayout.NORTH); //adds text field to top of Frame

add(keyPad, BorderLayout.CENTER); //center

add(keysArray[16], BorderLayout.EAST); //right side

for(int i = 0; i < keysArray.length; i++)

keysArray[i].addActionListener(this);

}

public void actionPerformed(ActionEvent e)

{

//Search for the key pressed

for (int i = 0; i < keysArray.length; i++)

{

if(e.getSource() == keysArray[i]) //key match found

{

            final double result1 = result;

switch(i)

{

case 0: case 1: case 2: case 3: case 4: //number buttons

case 5: case 6: case 7: case 8: case 9: //0-9

case 15:

    if (clearText)

    {

        Field.setText("");

        clearText = false;

    }

    Field.setText(Field.getText() + keysArray[i].getLabel());

    break;

case 10:// divide button

case 11:// multiply button

case 12:// minus button

case 13:// plus button

case 14:// equal button

    clearText = true;

    if (first) // First operand

    {

        if(Field.getText().length()==0)

            result = 0.0;

        else

            result = Double.valueOf(Field.getText()).doubleValue();

        first = false;

        prevOpe = i; //save previous operator

    }

    else //second operand already enter, so calculator total

    {

        switch(prevOpe)

        {

        case 10: //divide Button

            result /= Double.valueOf(Field.getText()).doubleValue();

            break;

        case 11: //multiply Button

            result *= Double.valueOf(Field.getText()).doubleValue();

            break;

        case 12: //minus button

            result -= Double.valueOf(Field.getText()).doubleValue();

            break;

        case 13: //plus button

            result += Double.valueOf(Field.getText()).doubleValue();

            break;

        }

        Field.setText(Double.toString(result));

        if (i==14)//equal button

            first = true;

        else

            prevOpe = i; //save previous opetator

    }

    break;

case 16://Clear button

    clearText = true;

    first = true;

    Field.setText("");

    result = 0.0;

    prevOpe = 0;

    break;

}

}

}

}

}