feat: Add Circle2 with encapsulation, validation, and geometry methods

WHAT the code does:
Defines Circle2 with private fields radius and color.
Provides:
- Constructor: initializes radius = 1.0 and color = "red".
- Getters: getRadius(), getColor() for controlled access.
- Setters: setRadius(double r) and setColor(String c) with validation logic.
Implements behavior methods:
- area(): computes circle area (πr²).
- circumference(): computes circle circumference (2πr).
Defines DataHidding1 with main():
- Creates a Circle2 object.
- Prints initial values using getters.
- Updates fields with valid inputs via setters.
- Demonstrates calculations for area and circumference.
- Attempts invalid inputs (negative radius, empty color) to show validation in action.

WHY this matters:
Demonstrates data hiding, a key OOP principle:
- Private fields prevent direct external modification.
- Public methods enforce controlled access with validation.
Shows how validation logic preserves object integrity (e.g., no negative radius or empty color).
Illustrates combining encapsulation with object behavior methods for real-world modeling.

HOW it works:
Constructor sets default values radius = 1.0, color = red.
Valid setter calls update values successfully (radius = 5.0, color = blue).
Invalid setter calls reset values to defaults with console messages.
area() and circumference() compute circle properties based on the current radius.
main() prints results before and after updates.

Tips and gotchas:
Validation currently resets to defaults silently after printing messages; throwing exceptions could be clearer in robust applications.
Comparing strings with null/empty check works here, but additional validation (e.g., restricting to known colors) could be added.
Overriding toString() would simplify printing circle details.
Fields could be made final with constructors for immutable design, if mutability isn’t needed.

Use-cases:
Educational example of encapsulation and data hiding in Java.
Practical model for geometric objects with validation logic.
Foundation for systems requiring controlled object state (e.g., graphics, simulations, GUIs).

Short key: class-circle2 encapsulation validation geometry.

Signed-off-by: https://github.com/Someshdiwan <[email protected]>

Author: Someshdiwan

Section11ObjectOrientedProgramming/src/DataHidding1.java

@@ -1,6 +1,86 @@
+/**
+ * This class demonstrates data hiding in Java
+ * Data hiding is achieved by:
+ * 1. Making instance variables private
+ * 2. Providing public getter and setter methods for controlled access
+ */
+class Circle2 {
+    // Private instance variables - hidden from outside access
+    private double radius;
+    private String color;
+    
+    // Public constructor
+    public Circle2() {
+        radius = 1.0;
+        color = "red";
+    }
+    
+    // Getter method for radius
+    public double getRadius() {
+        return radius;
+    }
+    
+    // Setter method for radius with validation
+    public void setRadius(double r) {
+        if (r > 0) {
+            radius = r;
+        } else {
+            System.out.println("Radius must be positive. Setting to default value 1.0");
+            radius = 1.0;
+        }
+    }
+    
+    // Getter method for color
+    public String getColor() {
+        return color;
+    }
+    
+    // Setter method for color
+    public void setColor(String c) {
+        if (c != null && !c.isEmpty()) {
+            color = c;
+        } else {
+            System.out.println("Color cannot be empty. Setting to default red");
+            color = "red";
+        }
+    }
+    
+    // Method to calculate area
+    public double area() {
+        return Math.PI * radius * radius;
+    }
+    
+    // Method to calculate circumference
+    public double circumference() {
+        return 2 * Math.PI * radius;
+    }
+}
 
 public class DataHidding1 {
     public static void main(String[] args) {
-
+        // Create a Circle object
+        Circle2 c1 = new Circle2();
+        
+        // Access data using public methods, not directly
+        System.out.println("Initial radius: " + c1.getRadius());
+        System.out.println("Initial color: " + c1.getColor());
+        
+        // Set new values using setter methods
+        c1.setRadius(5.0);
+        c1.setColor("blue");
+        
+        // Access the updated values
+        System.out.println("Updated radius: " + c1.getRadius());
+        System.out.println("Updated color: " + c1.getColor());
+        System.out.println("Area: " + c1.area());
+        System.out.println("Circumference: " + c1.circumference());
+        
+        // Attempt to set invalid values
+        c1.setRadius(-2.5);
+        c1.setColor("");
+        
+        // Check that validation worked
+        System.out.println("Radius after invalid input: " + c1.getRadius());
+        System.out.println("Color after invalid input: " + c1.getColor());
     }
 }