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

Quick links

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`. Circle formulas

## 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```

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