Java Program to Calculate Area of a Circle

The Mathematical formula to find Area of a Circle is : A= πr2 or we can write it as given below.
area = pi * radius * radius

So, to find Area of a circle we need the values of 'pi' and radius. In java we have predefined Mathematical value for pi is defined in java.lang.Math.PI = 3.141592653589793. PI is a static final value.

In our program we need to read radius value from the console by using BufferedReader or Console classes.

Here is the simple source code to find the area of the circle. Compiled successfully on windows operating system.

package com.javabynataraj;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
//http://javabynataraj.blogspot.com
public class AreaOfCircle {
 public static void main(String[] args) {
  int radius = 0;
  double area;
  System.out.print("Please enter radius of a circle: ");
  try {
   BufferedReader br = new BufferedReader(new InputStreamReader(
     System.in));
   radius = Integer.parseInt(br.readLine());
  }
  // if any invalid value entered
  catch (NumberFormatException ne) {
   System.out.println("Invalid radius value :"
     + "" + ne);
   System.exit(0);
  } catch (IOException ioe) {
   System.out.println("IO Error :" + ioe);
   System.exit(0);
  }

  area = Math.PI * radius * radius;
  System.out.println("Area of a circle is: " + area);
 }
}

After the compilation enter the radius value and press enter.
Output: