When you want to strengthen your basics of Java with the best projects, then a calculator in Java comes at the top of the list, which involves designing layouts, adding buttons, and making those buttons functional.
In this blog, I’ll explain how to create a simple yet powerful calculator in Java works, without going too deep into the code.
What Is Our Goal in this Calculator Project?
To make a basic calculator that has the following functionalities:
- Has a GUI to show numbers on the screen to present.
- Let our user enter the input and apply operation based on button pressed.
- Allow simple math operations like +, -, ×, ÷
- Show the result when the
=button is clicked
Step-by-Step Method to Create the Calculator in Java
Now, we’ll see all the top 5 steps to understand the logic and process to create a fully functional and powerful Java calculator in Java, along with the code logic.
Step 1: Create the Calculator Window GUI
Every app needs a window where everything appears. In Java, we can create such windows using built-in tools.
This is like creating a blank screen first, where we will later place all the buttons and the display.
We set the title of the window, its size, and what should happen when we close it.
Step 2: Adding the Calculator Display
At the top of the calculator, we need a display box, something like a screen where the numbers will show when we click the buttons.
It is worth to mention that our idea is not to show what we have typed on our computer’s keyboard, instead, we have to show things that we will type in the GUI Calculator keys buttons.
Step 3: Create the buttons
Our calculator will have the number buttons from 0 to 9, and it also has operation buttons like +, -, *, /, C, and =.
We arrange these buttons in a grid, like 4 rows and 4 columns. This way, the layout looks like a real calculator. Each button should respond when clicked. That means when you press a number, it should appear on the screen.
When you press an operation, like +, it should store the current number and wait for the next one. When you press =, it should calculate the result. And if you press C, everything should reset.
Step 4: Making Button Clicks Functional
Now, this step is the main logic part behind our calculator functioning:
Working Explained :
If a number is clicked, it gets added to the number already showing on the screen.
For example, if “2” is showing and you click “5”, the screen becomes “25”.
If an operator like +, -, *, or / is clicked, the calculator needs to:
- Remember the current number and remember which operator was clicked.
- Clear the screen so the user can type the second number.
When the user clicks =, the calculator:
- Takes the second number now shown on the screen, looks at the stored operator.
- Performs the correct math operation and shows the result on the screen.
If the user clicks C, the calculator:
Clears the screen, resets the first number, second number, and the operator.
This flow is repeated every time a new calculation is done.
Step 5: The Actual Coding Calculation
To perform the math, the calculator will take two numbers and an operator. Based on which operator was used, it chooses the correct formula.
For example:
If the operator is +, it adds the numbers.
If the operator is -, it subtracts the second number from the first.
If the operator is *, it multiplies.
If the operator is /, it divides (but only if the second number is not zero).
Once everything is set from the window, the buttons, the display to the logic, our final step now is to run the app.
Java Source Code: A Simple Calculator App in Java
Just create a Java file named ‘Calculator.java’ in VSCode and run using the command Ctrl+F5
import javax.swing.*;
import java.awt.*;
import java.awt.event.*;
public class Calculator extends JFrame implements ActionListener {
private JTextField display;
private String operator;
private double num1, num2;
public Calculator() {
setTitle("Java Calculator");
setSize(300, 400);
setDefaultCloseOperation(EXIT_ON_CLOSE);
setLocationRelativeTo(null);
display = new JTextField();
display.setEditable(false);
display.setFont(new Font("Arial", Font.PLAIN, 24));
add(display, BorderLayout.NORTH);
String[] buttons = {
"7", "8", "9", "/",
"4", "5", "6", "*",
"1", "2", "3", "-",
"0", "C", "=", "+"
};
JPanel panel = new JPanel();
panel.setLayout(new GridLayout(4, 4, 10, 10));
for (String text : buttons) {
JButton btn = new JButton(text);
btn.setFont(new Font("Arial", Font.BOLD, 20));
btn.addActionListener(this);
panel.add(btn);
}
add(panel);
setVisible(true);
}
@Override
public void actionPerformed(ActionEvent e) {
String input = ((JButton) e.getSource()).getText();
if (input.matches("[0-9]")) {
display.setText(display.getText() + input);
} else if (input.matches("[+\\-*/]")) {
operator = input;
num1 = Double.parseDouble(display.getText());
display.setText("");
} else if (input.equals("=")) {
num2 = Double.parseDouble(display.getText());
double result = calculate(num1, num2, operator);
display.setText(String.valueOf(result));
} else if (input.equals("C")) {
display.setText("");
num1 = num2 = 0;
operator = "";
}
}
private double calculate(double a, double b, String op) {
switch (op) {
case "+": return a + b;
case "-": return a - b;
case "*": return a * b;
case "/": return b != 0 ? a / b : 0;
default: return 0;
}
}
public static void main(String[] args) {
new Calculator();
}
}
GitHub Link for Calculator in Java Link
Conclusion
Making this project calculator in Java is a perfect project for building your Java basics and foundations. You get to create something visual, interactive, and useful. The process is fun and full of learning.
If you’re just starting your Java journey, this calculator is your first real step toward building software.
To get more such amazing beginner and expert Java projects, you may like these Java Projects.