# Java Program to calculate Perimeter/Circumference of Circle

One of the common programming exercise for beginners is to write a program to calculate the perimeter or circumference of a circle in Java. This exercise is not just common in Java but also on other programming language courses e.g. C, C++ or Python. I first did this exercise on C++ long ago, but that time the joy of a working program was something different. I was quite happy to see my program compiled without error and can print the correct circumference after entering radius. That program taught me how to take input from a user and how to display output into the console, I didn't know how to create methods to encapsulate code. For us, only main method matters at that time. Anyway, let's focus on the job at hand i.e. how to find the circumference of Circle of given radius. You have to accept radius from the user and show the output to console.

In order to calculate the perimeter of a circle, you must first remember the formula to calculate the circumference of a circle. Well, the formula is not difficult to remember, it's  2*PI*R, where PI is well-known Mathematics constant and R is the radius of the circle.

You can get the value of PI in Java by accessing Math.PI constant. Some programmer like to put the value of PI as 3.14 which is Ok for testing and demo, but not good for anything else. You should use the Math.PI wherever you need the value of PI in Java program.

## Java Program to calculate Circumference of circle

Now we need a value of radius which can be a user-provided value, alternatively, you can also pass in the program itself.

Let see the first option if we go by user value our program will prompt the user to enter a value for the radius. The Scanner class is used to take user input from the console it has many utility methods to get data from console later will convert user input to the desired form and then pass the radius to perimeter() function to calculate the circumference of the circle and store the result and valid variable.

now if we go the second option it's very simple in the program itself we can pass the value of radius and then use that value to calculate the perimeter of the circle and then display the result.

Here is our complete Java program to accept input from the user and print output into the console. We have used perimeter() function to calculate the circumference of the circle. This method returns a double value because PI is a floating point constant.

```mport java.util.Scanner;

/*
* Java Program to calculate circumference of circle
*/
public class Main {

public static void main(String args[]) {

//creating scanner to accept radius of circle
Scanner scanner = new Scanner(System.in);
System.out.println("Welcome in Java program to calculate Perimeter of circle");
System.out.println("Formula for calculating perimeter of circle is '2*PI*R' ");

System.out.println("Perimeter of Circle calculate by Java program is : "
+ perimeter);

scanner.close();
}

/*
* @return perimeter of a circle.
*/

}
}
```

You can run this program by copying the code into your favorite editor e.g. NotePad++ or IDE like Eclipse. You can also run it from the command line if you are not familiar with any IDE. In order to run from the command line, you also need to compile the class using javac command. This will produce the class file which you can run using java command as shown below:

```\$javac Main.java
\$java Main```

Remember, when we compile we provide the name of source file but when we run we provide the name of the class which contains main() method, This is the key difference between compiling and running a Java program. When you run, the program will produce following output:

```Welcome in Java program to calculate Perimeter of circle
Formula for calculating perimeter of circle is '2*PI*R'
4
Perimeter of Circle calculate by Java program is : 25.132741228718345```

You can see that user entered value of radius as 4 and program printed out the circumference of the circle as 25.13, which is correct as per following formula:

That's all about how to calculate the circumference or perimeter of the circle in Java. It's one of the simple Java programming exercises but really help you build your coding skill. You learn and understand how to use basic operators, API, and functions to solve some common mathematics problems. I strongly recommend Java beginners to solve as many problems as possible.

Further Learning
The Coding Interview Bootcamp: Algorithms + Data Structures
Data Structures and Algorithms: Deep Dive Using Java
Algorithms and Data Structures - Part 1 and 2

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Thanks for reading this article so far, if you like this article then please share with your friends and colleagues. If you have any questions or feedback then please drop a comment.  If you have just started learning Java and looking for a good book as a companion, I suggest you buy Head First Java, 2nd Edition, one of the best books to learn core Java from scratch.