Simple Calculator Example in Java

Introduction

Simple Calculator is a classic Java console program that demonstrates the concept with complete source code and sample output. Calculation programs apply formulas to solve geometry, statistics and numeric problems.

This tutorial walks through the program line by line, explains how the logic works, and highlights best practices you can apply in your own code.

Simple Calculator Example Program

import java.util.Scanner;
public class SimpleCalculator {
    public static void main(String[] args) {
        double n1, n2;
        String operation;
        Scanner in = new Scanner(System.in);
        System.out.println("Enter first number");
        n1 = in. nextDouble();
        System.out.println("Enter second number");
        n2 = in. nextDouble();
        System.out.println("Enter your operation");
        operation = in.next();
        switch (operation)  {
        case "+":
            System.out.println("Your answer is " + (n1 + n2));
            break;
        case "-":
            System.out.println("Your answer is " + (n1 - n2));
            break;
        case "/":
            System.out.println("Your answer is " + (n1 / n2));
            break;
        case "*":
            System.out.println("Your answer is " + (n1 * n2));
            break;
        default:
            System.out.println("Enter valid input");

        }
    }
}

Sample Output

Enter first number
56
Enter second number
77
Enter your operation
/
Your answer is 0.7272727272727273

When to use

Use these formulas in homework tools, engineering calculators or anywhere repeated numeric computation is needed.

How it works

1. Execution begins in the main method — the JVM calls this method when you run the class.

2. import java.util.Scanner; imports a class used later in the program.

3. A Scanner reads typed input from the keyboard (System.in).

4. A println / print call writes text to the console — part of the sample output below.

5. n1 = in. nextDouble(); updates a variable used in the calculation or output.

6. A println / print call writes text to the console — part of the sample output below.

7. n2 = in. nextDouble(); updates a variable used in the calculation or output.

8. A println / print call writes text to the console — part of the sample output below.

Best Practices

• Use meaningful variable and class names that describe their purpose.
• Compile and run the program locally — modify values to see how output changes.
• Read compiler errors carefully; they usually point to the exact line to fix.

Common Mistakes

• Copying code without understanding each line — practice by changing one statement at a time.
• Mismatching the public class name and the .java filename.
• Forgetting semicolons at the end of statements.