The formula for finding area of a circle is,

area = PI * radius * radius

Where PI is a constant (approximately 3.1416) and radius is the radius of the circle.

Calculate Area of a Circle in Java

The following Java program calculates the area of a circle given the radius of the circle. This program demonstrates a number of key concepts in Java programming,

• How to obtain user input from console
• How to write output to console
• How to use IO classes and decorator pattern
• Using library classes such as Math, BufferedReader, Double etc.
• Performing mathematical calculations

// Java program to calculate area of a circle
import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class CircleArea {
     public static void main(String[] args) throws IOException{
        
        BufferedReader reader = new BufferedReader(new InputStreamReader(System.in));
        System.out.print("Please enter the radius of the circle : ");
        double radius = Double.parseDouble(reader.readLine());
        
        double area = Math.PI * radius * radius;
        
        System.out.println("Area of the circle with radius "+radius+" is : "+area);
        
    }
}