Simple Calculator in Java Applet

Java Applet provides GUI way to create program and its interface, Here we are creating Simple Calculator in Java Applet with GUI and its processing.

As we have already learned about applet and applet life cycle.

Here we have discussed two simple calculator program using applet.

Simple applet- a beginner program
Simple Calculator – with calculator functionality

1 Simple calculator program in java using applet

Here we use a simple Applet with two Input box to get Input and result is shown on next input box.

To perform Addition, Subtraction, Multiplication and Division.

Four buttons bill be provided.

Added Action Listener to each button.

Based on button click public void actionPerformed(ActionEvent e) is get called and and based on event source appropriate if statement is executed.

Java applet program for calculator is as below

import java.awt.*;
import java.awt.event.*;
import java.applet.*;
/*  <applet code="Calculator" width="700" height="200">
  </applet>*/
public class Calculator extends Applet implements ActionListener {
    String msg = "";
    TextField t1, t2, t3;
    Button b1, b2, b3, b4;
    Label l1, l2, l3;
    public void init() {
        l1 = new Label("First Number");
        add(l1);
        t1 = new TextField(15);
        add(t1);
        l2 = new Label("Second Number");
        add(l2);
        t2 = new TextField(15);
        add(t2);
        l3 = new Label("Result");
        add(l3);
        t3 = new TextField(15);
        add(t3);
        b1 = new Button("ADD");
        add(b1);
        b1.addActionListener(this);
        b2 = new Button("SUB");
        add(b2);
        b2.addActionListener(this);
        b3 = new Button("MULT");
        add(b3);
        b3.addActionListener(this);
        b4 = new Button("DIV");
        add(b4);
        b4.addActionListener(this);
    }
    public void actionPerformed(ActionEvent e) {
        if (e.getSource() == b1) {
            int x = Integer.parseInt(t1.getText());
            int y = Integer.parseInt(t2.getText());
            int sum = x + y;
            t3.setText(" " + sum);
        }
        if (e.getSource() == b2) {
            int x = Integer.parseInt(t1.getText());
            int y = Integer.parseInt(t2.getText());
            int sub = x - y;
            t3.setText(" " + sub);
        }
        if (e.getSource() == b3) {
            int x = Integer.parseInt(t1.getText());
            int y = Integer.parseInt(t2.getText());
            int mul = x * y;
            t3.setText(" " + mul);
        }
        if (e.getSource() == b4) {
            int x = Integer.parseInt(t1.getText());
            int y = Integer.parseInt(t2.getText());
            int div = x / y;
            t3.setText(" " + div);
        }
        showStatus(" text & button example");
        repaint();
    }
}

import java.awt.*;

import java.awt.event.*;

import java.applet.*;

/* <applet code="Calculator" width="700" height="200">

</applet>*/

public class Calculator extends Applet implements ActionListener {

String msg = "";

TextField t1, t2, t3;

Button b1, b2, b3, b4;

Label l1, l2, l3;

public void init() {

l1 = new Label("First Number");

add(l1);

t1 = new TextField(15);

add(t1);

l2 = new Label("Second Number");

add(l2);

t2 = new TextField(15);

add(t2);

l3 = new Label("Result");

add(l3);

t3 = new TextField(15);

add(t3);

b1 = new Button("ADD");

add(b1);

b1.addActionListener(this);

b2 = new Button("SUB");

add(b2);

b2.addActionListener(this);

b3 = new Button("MULT");

add(b3);

b3.addActionListener(this);

b4 = new Button("DIV");

add(b4);

b4.addActionListener(this);

}

public void actionPerformed(ActionEvent e) {

if (e.getSource() == b1) {

int x = Integer.parseInt(t1.getText());

int y = Integer.parseInt(t2.getText());

int sum = x + y;

t3.setText(" " + sum);

}

if (e.getSource() == b2) {

int x = Integer.parseInt(t1.getText());

int y = Integer.parseInt(t2.getText());

int sub = x - y;

t3.setText(" " + sub);

}

if (e.getSource() == b3) {

int x = Integer.parseInt(t1.getText());

int y = Integer.parseInt(t2.getText());

int mul = x * y;

t3.setText(" " + mul);

}

if (e.getSource() == b4) {

int x = Integer.parseInt(t1.getText());

int y = Integer.parseInt(t2.getText());

int div = x / y;

t3.setText(" " + div);

}

showStatus(" text & button example");

repaint();

}

Below is the output of the calculator program in java

Simple Calculator in Java Applet — Java Applet Simple Calculator Example

Above Example is create to learn Basic Functionality.

2 Java applet program for calculator

This GUI looks like a real calculator. Here all values are input through button click.

Here We have created buttons for 0-9 input.

Operator buttons +, -, *, /, % and =.

Also provided button for AC, BSp, . (dot), and RSET (Reset).

Functions of these button are

AC– Clear the Input Text Field.

BSp– Backspace used to remove a character from input string.

dot(.)– Dot is used for decimal number.

RSET-Reset both text box input and result box.

All Above Features are included in Example.

Additional Feature of this calculator is that it can accept multiple input with different operators.

After adding all numbers it shows the result in top text box.

Simple Calculator Code

Created Layout with two text box and numbers and special buttons like AC, BSp.
Add add buttons to actionListener b[i].addActionListener(this);
Create actionPerformed to get actionCommand()
Define work for =, AC, BSp and RESET
On = arithmetic calculation should be done that is handled by calculate()
On calculate() use ScriptEngineManager for calculation

Calculator.java

import java.applet.Applet;
import java.awt.Graphics;
import java.awt.Button;
import java.awt.Frame;
import java.awt.TextField;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import javax.script.ScriptEngine;
import javax.script.ScriptEngineManager;
import javax.script.ScriptException;

public class Calculator extends Applet implements ActionListener {

    public static final String[] TEXT = {"AC", "BSp", "%", "/", "7", "8", "9", "*", "4", "5", "6", "-", "1", "2", "3", "+", "RSET", "0", ".", "="};
    TextField t1;
    TextField t2;
    StringBuffer value = new StringBuffer();

    public void init() {
        Frame title = (Frame) this.getParent().getParent();
        title.setTitle("Simple Calculator");
        setLayout(null);
        t1 = new TextField("", 4);
        t1.setBounds(50, 10, 200, 50);
        add(t1);
        t2 = new TextField("", 4);
        t2.setBounds(50, 60, 200, 50);
        add(t2);
        int x = 50;
        int y = 115;
        int k = 1;
        Button b[] = new Button[20];
        for (int i = 0; i < TEXT.length; i++) {
            b[i] = new Button("" + TEXT[i]);
            b[i].setBounds(x * k, y, 50, 50);

            if (k % 4 == 0) {
                x = 50;
                y += 50;
                k = 0;
            }
            k++;
            add(b[i]);
            b[i].addActionListener(this);

        }
    }

    public void paint(Graphics g) {

    }

    public void actionPerformed(ActionEvent e) {
        String s = e.getActionCommand();
        if (s.equalsIgnoreCase("=")) {
            System.out.println("generating result");
            t1.setText(calculate(value));
            value.setLength(0);
        } else if (s.equalsIgnoreCase("AC")) {
            System.out.println("AC: Resetting Input");
            value.setLength(0);
            t2.setText("");
        } else if (s.equalsIgnoreCase("BSp")) {
            System.out.println("BSp: Erasing a character");
            value.setLength(value.length() - 1);
            t2.setText(value.toString());
        } else if (s.equalsIgnoreCase("RSET")) {
            System.out.println("Reset: Resetting Input output ");
            value.setLength(0);
            t1.setText("");
            t2.setText("");
        } else {
            value.append(s);
            t2.setText(value.toString());
        }
    }

    public String calculate(StringBuffer sb) {
        ScriptEngineManager mgr = new ScriptEngineManager();
        ScriptEngine engine = mgr.getEngineByName("JavaScript");
        Object result = null;
        try {
            result = engine.eval(sb.toString());
            System.out.println(result);
        } catch (ScriptException ex) {
            System.out.println("Exception : Check again your operator sequence");
            result = "Error";
        }
        return result.toString();
    }

}

import java.applet.Applet;

import java.awt.Graphics;

import java.awt.Button;

import java.awt.Frame;

import java.awt.TextField;

import java.awt.event.ActionEvent;

import java.awt.event.ActionListener;

import javax.script.ScriptEngine;

import javax.script.ScriptEngineManager;

import javax.script.ScriptException;

public class Calculator extends Applet implements ActionListener {

public static final String[] TEXT = {"AC", "BSp", "%", "/", "7", "8", "9", "*", "4", "5", "6", "-", "1", "2", "3", "+", "RSET", "0", ".", "="};

TextField t1;

TextField t2;

StringBuffer value = new StringBuffer();

public void init() {

Frame title = (Frame) this.getParent().getParent();

title.setTitle("Simple Calculator");

setLayout(null);

t1 = new TextField("", 4);

t1.setBounds(50, 10, 200, 50);

add(t1);

t2 = new TextField("", 4);

t2.setBounds(50, 60, 200, 50);

add(t2);

int x = 50;

int y = 115;

int k = 1;

Button b[] = new Button[20];

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

b[i] = new Button("" + TEXT[i]);

b[i].setBounds(x * k, y, 50, 50);

if (k % 4 == 0) {

x = 50;

y += 50;

k = 0;

}

k++;

add(b[i]);

b[i].addActionListener(this);

}

public void paint(Graphics g) {

}

public void actionPerformed(ActionEvent e) {

String s = e.getActionCommand();

if (s.equalsIgnoreCase("=")) {

System.out.println("generating result");

t1.setText(calculate(value));

value.setLength(0);

} else if (s.equalsIgnoreCase("AC")) {

System.out.println("AC: Resetting Input");

value.setLength(0);

t2.setText("");

} else if (s.equalsIgnoreCase("BSp")) {

System.out.println("BSp: Erasing a character");

value.setLength(value.length() - 1);

t2.setText(value.toString());

} else if (s.equalsIgnoreCase("RSET")) {

System.out.println("Reset: Resetting Input output ");

value.setLength(0);

t1.setText("");

t2.setText("");

} else {

value.append(s);

t2.setText(value.toString());

}

public String calculate(StringBuffer sb) {

ScriptEngineManager mgr = new ScriptEngineManager();

ScriptEngine engine = mgr.getEngineByName("JavaScript");

Object result = null;

try {

result = engine.eval(sb.toString());

System.out.println(result);

} catch (ScriptException ex) {

System.out.println("Exception : Check again your operator sequence");

result = "Error";

}

return result.toString();

}

In Java ScriptEngineManager is used for expression calculation.

That makes our calculation part easy.

1 Simple calculator program in java using applet

2 Java applet program for calculator

Simple Calculator Code

Calculator.java

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