Creating a Simple Calculator in Java

A calculator is a fundamental project for anyone learning a new programming language. It allows you to practice basic programming concepts such as variables, control structures, loops and functions. In this article, we will create a simple calculator in Java that can perform basic arithmetic operations such as addition, subtraction, multiplication and division.

Prerequisites

• Java Development Kit (JDK) installed on the computer.
• An Integrated Development Environment (IDE) like IntelliJ IDEA, Eclipse or a simple text editor and command line for compiling Java code.

Step-by-Step Guide

Step 1: Setting Up Your Project

1. Create a New Java Project: Open your IDE and create a new Java project. Name it Calculator.
2. Create a New Java Class: Inside your project create a new Java class. Name it Calculator.

Step 2: Writing the Calculator Code

Let's start by writing the code for our calculator.

import java.util.Scanner;

public class Calculator {

    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);

        System.out.println("Enter first number: ");
        double num1 = scanner.nextDouble();

        System.out.println("Enter second number: ");
        double num2 = scanner.nextDouble();

        System.out.println("Enter an operator (+, -, *, /): ");
        char operator = scanner.next().charAt(0);

        double result;

        switch (operator) {
            case '+':
                result = num1 + num2;
                break;
            case '-':
                result = num1 - num2;
                break;
            case '*':
                result = num1 * num2;
                break;
            case '/':
                if (num2 != 0) {
                    result = num1 / num2;
                } else {
                    System.out.println("Error! Division by zero is not allowed.");
                    return;
                }
                break;
            default:
                System.out.println("Invalid operator!");
                return;
        }

        System.out.println("The result is: " + result);
    }
}

Output :
Enter first number: 
10
Enter second number: 
20
Enter an operator (+, -, *, /): 
+
The result is: 30.0

Explanation of the Code

1. Importing the Scanner Class:

import java.util.Scanner;

The Scanner class is used to take input from the user.

2. Main Method:

public static void main(String[] args) {

This is the entry point of our program.

3. Creating Scanner Object:

Scanner scanner = new Scanner(System.in);

We create an instance of Scanner to read user inputs.

4. Taking User Inputs:

System.out.println("Enter first number: ");
double num1 = scanner.nextDouble();

We prompt the user to enter the first number and store it in num1.

System.out.println("Enter second number: ");
double num2 = scanner.nextDouble();

Similarly, we prompt the user to enter the second number and store it in num2.

System.out.println("Enter an operator (+, -, *, /): ");
char operator = scanner.next().charAt(0);

We prompt the user to enter an operator and store it in operator.

5. Switch Case for Operations:

switch (operator) {
    case '+':
        result = num1 + num2;
        break;
    case '-':
        result = num1 - num2;
        break;
    case '*':
        result = num1 * num2;
        break;
    case '/':
        if (num2 != 0) {
            result = num1 / num2;
        } else {
            System.out.println("Error! Division by zero is not allowed.");
            return;
        }
        break;
    default:
        System.out.println("Invalid operator!");
        return;
}

We use a switch case to perform the operation based on the operator entered by the user.

6. Displaying the Result:

System.out.println("The result is: " + result);

We print the result of the operation.

Running the Calculator

1. Compile the Program: If using a command line, navigate to the directory containing your Calculator.java file and compile it using:

javac Calculator.java

2. Run the Program: After compiling, run the program using:

java Calculator

3. Enter Inputs: Follow the prompts to enter two numbers and an operator. The program will display the result of the operation.

Conclusion

Creating a simple calculator in Java is a great way to practice basic programming concepts and get familiar with taking user inputs and performing operations. This project foundation for more complex applications and helps build a strong understanding of Java syntax and control structures.