Java Encapsulation: Implementing a circle class with getter, setter, and calculation methods

Last update on May 16 2025 13:08:11 (UTC/GMT +8 hours)

Write a Java program to create a class called Circle with a private instance variable radius. Provide public getter and setter methods to access and modify the radius variable. However, provide two methods called calculateArea() and calculatePerimeter() that return the calculated area and perimeter based on the current radius value.

Sample Solution:

Java Code:

// Circle.java

// Circle Class
class Circle {
  // Declare a private double variable for radius
  private double radius;

  // Getter method for radius
  public double getRadius() {
    return radius;
  }

  // Setter method for radius
  public void setRadius(double radius) {
    this.radius = radius;
  }

  // Method to calculate the area of the circle
  public double calculateArea() {
    return Math.PI * radius * radius;
  }

  // Method to calculate the perimeter (circumference) of the circle
  public double calculatePerimeter() {
    return 2 * Math.PI * radius;
  }
}

// Main.java
// Main Class

public class Main {
    public static void main(String[] args) {
        // Create an instance of Circle
        Circle circle = new Circle();

        // Set the radius using the setter method
        circle.setRadius(7.0);

        // Get the radius using the getter method
        double radius = circle.getRadius();

        // Calculate and print the area and perimeter
        double area = circle.calculateArea();
        double perimeter = circle.calculatePerimeter();

        System.out.println("Circle Radius: " + radius);
        System.out.println("Circle Area: " + area);
        System.out.println("Circle Perimeter: " + perimeter);
    }
}

Output:

Circle Radius: 7.0
Circle Area: 153.93804002589985
Circle Perimeter: 43.982297150257104

Explanation:

In the above exercise,

In this code, the Circle class encapsulates the private instance variable radius. The getRadius() and setRadius() methods are public getter and setter methods that allow other classes to access and modify radius values, respectively.

Additionally, the Circle class provides two public methods calculateArea() and calculatePerimeter() that calculate and return the area and perimeter of the circle. These methods are based on the current radius value. These methods use the formula Math.PI*radius*radius for area calculation and 2*Math.PI*radius for perimeter calculation.

In the Main class, an object circle of the Circle class is created. The circle radius is set using the setRadius() method, and then retrieved using the getRadius() method.

The area and perimeter of the circle are calculated using the calculateArea() and calculatePerimeter() methods, respectively, and printed using System.out.println().

Flowchart:

Flowchart: Java Encapsulation: Implementing a circle class with getter, setter, and calculation methods.

For more Practice: Solve these Related Problems:

Write a Java program where the "Circle" class prevents setting a negative radius.
Write a Java program where the "Circle" class calculates the circumference using a separate method.
Write a Java program where the "Circle" class includes a method to determine if one circle can fit inside another.
Write a Java program where the "Circle" class supports resizing the radius with a scale factor.

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