Area of Circle Example in Java

Introduction

Area Of Circle 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.

Definition

The area of a circle is ? (Pi) times the Radius squared,which is written A=?r2.

Formula

The area of a circle is written
A=?r2

here,
r = Radius
? = ~3.14

Area Of Circle Example Program

import java.util.Scanner;

class AreaOfCircle{
	Scanner in = new Scanner(System.in);
	public static void main(String args[]){
		System.out.print("Enter the radius: ");
		double radius = in.nextDouble();
		double area = Math.PI * (radius * radius);
		System.out.println("The area of circle is: " + area);
	}
}

Sample Output

Enter the radius: 4
The area of circle is: 50.26548245743669

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. double radius = in.nextDouble(); updates a variable used in the calculation or output.

6. double area = Math.PI * (radius * radius); updates a variable used in the calculation or output.

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

8. Compare your console output with the sample output for Area Of Circle to confirm the program behaves correctly.

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.