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.

**Example**

**Input**

Enter radius of circle : 6

**Output**

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.

Output

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 ðŸ˜‰