Java program to find diameter, circumference and area of circle

Write a Java program to input radius of circle and find diameter, circumference and area of circle. Logic to find diameter circumference and area of circle.

Enter radius of circle : 6

Diameter of circle is : 20
Circumference of circle is : 62.8318
Area of circle is : 314.159

Required knowledge

Arithmetic operators, Data types, Basic Input/Output

Components of circle

Before we write Java code, let us recall basic components of circle. And how they are mathematically related with each other.

• A circle has a radius, denoted with letter r in mathematics.
• Circle has a diameter, denoted by letter d. Relation between diameter and radius of circle is given by the equation d = 2 * r.
• Circumference is the boundary of circle. Formulae for calculating circumference is written as circumference = 2 * PI * r. Here PI is constant equal to 3.141592653.
• Area of circle is evaluated by equation area = PI * r * r.

Program to find diameter circumference and area of circle

/**
 * Program to find diameter, circumference and area of circle.
 */
import java.util.Scanner;

public class Circle {

    public static void main(String[] args) {

        // Declare constant for PI
        final double PI = 3.141592653;

        Scanner in = new Scanner(System.in);

        /* Input radius of circle from user. */
        System.out.println("Please enter radius of the circle : ");
        int r = in.nextInt();

        /* Calculate diameter, circumference and area. */
        int d = 2 * r;
        double circumference = 2 * PI * r;
        double area = PI * r * r;


        /* Print diameter, circumference and area of circle. */
        System.out.println("Diameter of circle is : " + d);
        System.out.println("Circumference of circle is : " + circumference);
        System.out.println("Area of circle is : " + area);
    }
}

Here we are declaring a constant variable PI through final keyword.

Instead of declaring our custom constant for PI, we can Java predefined constant for PI, defined in Math class i.e. Math.PI.

Math is built-in class in java, available in java.lang package. PI is a static final double type variable of Math. Because PI is static, so we can use it without creating object of Math class. And PI is final also, so we cannot change its value in our program.

Please enter radius of the circle : 20
Diameter of circle is : 40
Circumference of circle is : 125.66370612
Area of circle is : 1256.6370612

Happy coding 😉