Introduction of the Project

If you’re looking to dive into the basics of Java and want to create a practical application, then building a simple calculator is a fantastic starting point. Calculators are fundamental tools used in many applications, and building one in Java can be a great way to improve your programming skills. As a Java expert, let me guide you through the process of developing a simple calculator using Java.

In this guide, we’ll walk you through the step-by-step process of developing a simple calculator using Java. You’ll learn how to set up your Java development environment, create a Java class, get user input, perform calculations, display results, add error handling, and test your program. Whether you’re a beginner or an experienced Java developer, this guide will provide you with the knowledge and tools to build a functional calculator that you can be proud of.

So, let’s dive in and unlock the world of Java programming as we start on this exciting journey to develop a simple calculator that showcases the power and versatility of Java!

Objectives

1. To implement the right mathematics to solve simple problems of addition, subtraction, multiplication, and division.

2. To create a graphic user interface (GUI) involving some graphics, along with the fundamental calculator logic, to give users a good interface to work with.

Requirements

Source Code

// Java program to create a simple calculator
// with basic +, -, /, * using java swing elements


import java.awt.event.*;
import javax.swing.*;
import java.awt.*;
class calculator extends JFrame implements ActionListener {
// Creating a frame
static JFrame f;


// Creating a textfield
static JTextField l;


// storing operator and operands
String s0, s1, s2;


// The default constructor
calculator()
{
s0 = s1 = s2 = "";
}


// Main function
public static void main(String args[])
{
// create a frame
f = new JFrame("calculator");


try {
// Setting the look & feel
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
}
catch (Exception e) {
System.err.println(e.getMessage());
}


// creating an object of class
calculator c = new calculator();


// creating a textfield
l = new JTextField(16);


// setting the textfield to non-editable
l.setEditable(false);


// creating buttons for the numbers and operators
JButton b0, b1, b2, b3, b4, b5, b6, b7, b8, b9, ba, bs, bd, bm, be, beq, beq1;


// number buttons
b0 = new JButton("0");
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");


// creating the equals to button
beq1 = new JButton("=");


// creating buttons for the operator
ba = new JButton("+");
bs = new JButton("-");
bd = new JButton("/");
bm = new JButton("*");
beq = new JButton("C");


// creating decimal "." button
be = new JButton(".");


// creating one panel
JPanel p = new JPanel();


// adding the action listeners
bm.addActionListener(c);
bd.addActionListener(c);
bs.addActionListener(c);
ba.addActionListener(c);
b9.addActionListener(c);
b8.addActionListener(c);
b7.addActionListener(c);
b6.addActionListener(c);
b5.addActionListener(c);
b4.addActionListener(c);
b3.addActionListener(c);
b2.addActionListener(c);
b1.addActionListener(c);
b0.addActionListener(c);
be.addActionListener(c);
beq.addActionListener(c);
beq1.addActionListener(c);


// adding different elements to the panel
p.add(l);
p.add(ba);
p.add(b1);
p.add(b2);
p.add(b3);
p.add(bs);
p.add(b4);
p.add(b5);
p.add(b6);
p.add(bm);
p.add(b7);
p.add(b8);
p.add(b9);
p.add(bd);
p.add(be);
p.add(b0);
p.add(beq);
p.add(beq1);


// setting the Background of the panel
p.setBackground(Color.blue);


// adding the panel to the frame
f.add(p);


f.setSize(200, 220);
f.show();
}
public void actionPerformed(ActionEvent e)
{
String s = e.getActionCommand();


// if the value entered is a number
if ((s.charAt(0) >= '0' && s.charAt(0) <= '9') || s.charAt(0) == '.') {
// if operand is present then add to second number
if (!s1.equals(""))
s2 = s2 + s;
else
s0 = s0 + s;


// setting the value of the text
l.setText(s0 + s1 + s2);
}
else if (s.charAt(0) == 'C') {
// clearing the one letter
s0 = s1 = s2 = "";


// set the value of text
l.setText(s0 + s1 + s2);
}
else if (s.charAt(0) == '=') {


double te;


// store the value in 1st
if (s1.equals("+"))
te = (Double.parseDouble(s0) + Double.parseDouble(s2));
else if (s1.equals("-"))
te = (Double.parseDouble(s0) - Double.parseDouble(s2));
else if (s1.equals("/"))
te = (Double.parseDouble(s0) / Double.parseDouble(s2));
else
te = (Double.parseDouble(s0) * Double.parseDouble(s2));


// set the value of text
l.setText(s0 + s1 + s2 + "=" + te);


// converting it to string
s0 = Double.toString(te);


s1 = s2 = "";
}
else {
// if there was no operand
if (s1.equals("") || s2.equals(""))
s1 = s;
// else evaluate
else {
double te;


// store the value in 1st
if (s1.equals("+"))
te = (Double.parseDouble(s0) + Double.parseDouble(s2));
else if (s1.equals("-"))
te = (Double.parseDouble(s0) - Double.parseDouble(s2));
else if (s1.equals("/"))
te = (Double.parseDouble(s0) / Double.parseDouble(s2));
else
te = (Double.parseDouble(s0) * Double.parseDouble(s2));


// convert it to string
s0 = Double.toString(te);


// place the operator
s1 = s;


// make the operand blank
s2 = "";
}


// set the value of text
l.setText(s0 + s1 + s2);
}
}
}

Explanation of the Code

Since we will be using Swing to create the GUI of the application, you can imagine that will be the major chunk of the program as the mathematics is pretty simple since we will restrict this basic calculator to +, -, *, and / operations.

1. For the GUI, we will start by creating buttons for all the digits from 0-9. We will also create buttons for the operands such as +, -, *, and /.

2. The application will have a button to clear the values from the “display” of the calculator application.

3. We will also use a text field that will be set to uneditable. This text field will become the display of the calculator.

4. Once all the buttons have been created and laid out in the JFrame, the buttons will be functionalized using the addActionListener (ActionListener d) function.

5. Whenever a button containing any digit is pressed, we will go to an “IF statement” that will store it in a variable. If an operator button is pressed, it will be stored as a string again.

6. If the “=” button is pressed, the program will check for what kind of operation and perform the operation. The output will be converted back to string and displayed as output.

Output

Addition

Multiplication

We have successfully developed a simple calculator using Java and Swing frameworks. While this is a basic version with few operations, the same logic can also be extended to create a scientific calculator.

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Vaibhav Mandhani

As a passionate Java developer with over 10 years of experience, I live and breathe Java programming. I have a deep understanding of Java core concepts such as object-oriented programming, multithreading, exception handling, and Java collections. I am proficient in using Java libraries, frameworks, and tools and can write clean, efficient, and maintainable Java code. I can design and implement RESTful APIs, work with databases, and integrate with various third-party services.