# Java: Find the area and perimeter of a circle

## Java Basic: Exercise-11 with Solution

Write a Java program to print the area and perimeter of a circle.

In geometry, the area enclosed by a circle of radius r is πr^{2}. Here the Greek letter π represents a constant, approximately equal to 3.14159, which is equal to the ratio of the circumference of any circle to its diameter.

The circumference of a circle is the linear distance around its edge.

**Pictorial Presentation:**

Why is the area of a circle of a circle pi times the square of the radius?

**Sample Solution-1**

**Java Code:**

```
public class Exercise11 {
// Define a constant for the radius of the circle
private static final double radius = 7.5;
public static void main(String[] args) {
// Calculate the perimeter of the circle using the constant radius
double perimeter = 2 * Math.PI * radius;
// Calculate the area of the circle using the constant radius
double area = Math.PI * radius * radius;
// Print the calculated perimeter and area
System.out.println("Perimeter is = " + perimeter);
System.out.println("Area is = " + area);
}
}
```

**Explanation:**

In the exercise above -

The above Java code calculates and prints the perimeter and area of a circle with a given radius (in this case, a radius of 7.5 units). It uses mathematical constants and formulas for circles:

- It calculates the perimeter (circumference) using the formula: 2 * Math.PI * radius;
- It calculates the area using the formula: π * radius^2.

The perimeter and area values are then printed to the console.

Sample Output:

Perimeter is = 47.12388980384689 Area is = 176.71458676442586

**Flowchart: **

**Sample Solution-2**

**Java Code:**

```
import java.util.Scanner;
public class Main {
public static void main(String[] args) {
// Create a Scanner object to read input from the user
Scanner io = new Scanner(System.in);
// Prompt the user to input the radius of the circle
System.out.println("Input the radius of the circle: ");
// Read and store the input radius
double radius = io.nextDouble();
// Calculate and print the perimeter of the circle
System.out.println("Perimeter is = " + (2 * radius * Math.PI));
// Calculate and print the area of the circle
System.out.println("Area is = " + (Math.PI * radius * radius));
}
}
```

Sample Output:

Input the radius of the circle: 5 Perimeter is = 31.41592653589793 Area is = 78.53981633974483

**Flowchart: **

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