Java Program to Implement a Circle Class

Question: Java Program to Implement a Circle Class

Task:
Write a Java class to represent a circle. Your class should:

1. Store the radius of the circle.

2. Provide a method to display the radius.

3. Provide a method to calculate and display the area of the circle.

4. Provide a method to calculate and display the perimeter (circumference) of the circle.

Hints / Help Points:

• Use a variable radius to store the circle’s radius.

• Use Math.PI to calculate the area and perimeter.

• Area = π × radius × radius

• Perimeter = 2 × π × radius

Example Usage:

Circle c = new Circle(5);
c.displayRadius();    // Output: Radius: 5
c.displayArea();      // Output: Area: 78.54
c.displayPerimeter(); // Output: Perimeter: 31.42

Solution:

// Circle class
class Circle {
    private double radius;

    // Constructor
    public Circle(double radius) {
        this.radius = radius;
    }

    // Method to display radius
    public void displayRadius() {
        System.out.println("Radius: " + radius);
    }

    // Method to display area
    public void displayArea() {
        double area = Math.PI * radius * radius;
        System.out.println("Area: " + area);
    }

    // Method to display perimeter
    public void displayPerimeter() {
        double perimeter = 2 * Math.PI * radius;
        System.out.println("Perimeter: " + perimeter);
    }
}

// Test class
public class TestCircle {
    public static void main(String[] args) {
        Circle c1 = new Circle(5);

        c1.displayRadius();    // Radius: 5
        c1.displayArea();      // Area: 78.53981633974483
        c1.displayPerimeter(); // Perimeter: 31.41592653589793
    }
}

Explanation:

1. Circle class stores the radius in a private variable.

2. Constructor initializes the radius.

3. displayRadius() prints the radius.

4. displayArea() calculates and prints the area using Math.PI.

5. displayPerimeter() calculates and prints the perimeter using 2 × π × radius.