Java program to calculate the diameter, circumference and area of circle

The program asks the user to enter the radius of a circle and finds the diameter, circumference and area. 

Diameter, area and circumference formulas:

Diameter = 2 * Radius

Area = π * Radius²

Circumference = 2 * π * Radius

We can use the floating-point value 3.1416 for π but in this program we use the Java predefined constant Math.PI.

Area = Math.PI * Radius²;

Circumference = 2 * Math.PI * Radius;

Java program to find diameter, circumference and area of circle:

//diameter, area and circumference of circle 
import java.util.Scanner;
public class JavaCircle {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double radius, diameter, circumference, area;

        System.out.print("Enter the radius: ");
        radius = sc.nextDouble();

        diameter = 2 * radius;
        System.out.println("Diameter: " + diameter);

        circumference = 2 * Math.PI * radius;
        System.out.println("Circumference: " + circumference);                                                    

        area = Math.PI * radius * radius;
        System.out.println("Area: " + area);

    }
}

Sample output: :

Enter the radius: 2,5     
Diameter: 5.0
Circumference: 15.707963267948966     
Area: 19.634954084936208

We can use the printf method to display the result with only two decimal places instead of the default decimal places.

This is the statement to display the diameter with two decimal places:

System.out.printf("Diameter: %.2f\n" , diameter);

% indicates that a value will be displayed here, in this case, diameter.

.2 indicates the decimal places to display

f indicates a floating-point value

Java program to find diameter, circumference and area of circle with two decimal places using System.out.printf:

//diameter, area and circumference of circle using System.out.printf
import java.util.Scanner;
public class JavaCircle {
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        double radius, diameter, circumference, area;

        System.out.print("Enter the radius: ");
        radius = sc.nextDouble();

        diameter = 2 * radius;
        System.out.printf("Diameter: %.2f\n" , diameter);

        circumference = 2 * Math.PI * radius;
        System.out.printf("Circumference: %.2f\n" , circumference);                                               

        area = Math.PI * radius * radius;
        System.out.printf("Area: %.2f\n" , area);

    }
}

Sample output: :

Enter the radius: 2,5   
Diameter: 5,00
Circumference: 15,71          
Area: 19,63