Answer: Java Program — Figure Hierarchy with Dynamic Method Dispatch

1. Problem Specification

• Superclass: Figure
  • Instance variables: dim1, dim2 (dimensions of a 2D geometric object).
  • Method: area() returning double.
• Subclasses:
  • Rectangle: Overrides area() to compute $\text{Length} \times \text{Breadth} = \text{dim1} \times \text{dim2}$.
  • Triangle: Overrides area() to compute $\frac{1}{2} \times \text{Base} \times \text{Height} = 0.5 \times \text{dim1} \times \text{dim2}$.
• Driver Class: Demonstrates Dynamic Method Dispatch (Runtime Polymorphism).

                           +------------------------+
                           |         Figure         |
                           |------------------------|
                           | double dim1, dim2      |
                           | double area()          |
                           +-----------+------------+
                                       |
                     +-----------------+-----------------+
                     |                                   |
                     v                                   v
             +---------------+                   +---------------+
             |   Rectangle   |                   |   Triangle    |
             |---------------|                   |---------------|
             | double area() |                   | double area() |
             | (dim1 * dim2) |                   | (0.5*dim1*dim2|
             +---------------+                   +---------------+

---

2. Complete Java Program

// Superclass Figure
class Figure {
    double dim1;
    double dim2;

    // Parameterized constructor to initialize dimensions
    Figure(double dim1, double dim2) {
        this.dim1 = dim1;
        this.dim2 = dim2;
    }

    // Base area method (to be overridden by subclasses)
    double area() {
        System.out.println("Area for generic Figure is undefined.");
        return 0;
    }
}

// Subclass Rectangle overriding area()
class Rectangle extends Figure {
    Rectangle(double length, double breadth) {
        super(length, breadth); // Pass dimensions to superclass
    }

    // Overriding area() for rectangle: length * breadth
    @Override
    double area() {
        System.out.println("Calculating Area of Rectangle:");
        return dim1 * dim2;
    }
}

// Subclass Triangle overriding area()
class Triangle extends Figure {
    Triangle(double base, double height) {
        super(base, height); // Pass dimensions to superclass
    }

    // Overriding area() for triangle: 1/2 * base * height
    @Override
    double area() {
        System.out.println("Calculating Area of Triangle:");
        return 0.5 * dim1 * dim2;
    }
}

// Driver Class to test polymorphism
public class FigureAreaDemo {
    public static void main(String[] args) {
        // Instantiate specific shape objects
        Figure genericFig = new Figure(10, 10);
        Rectangle rect = new Rectangle(12.0, 8.0);
        Triangle tri = new Triangle(10.0, 6.0);

        // Reference variable of superclass Figure
        Figure figRef;

        System.out.println("========================================");
        System.out.println("   DYNAMIC METHOD DISPATCH DEMO");
        System.out.println("========================================
");

        // 1. Superclass reference pointing to Rectangle object
        figRef = rect;
        System.out.println("Rectangle Dimensions: [Length = " + rect.dim1 + ", Breadth = " + rect.dim2 + "]");
        System.out.println("Computed Area = " + figRef.area() + " sq units
");

        // 2. Superclass reference pointing to Triangle object
        figRef = tri;
        System.out.println("Triangle Dimensions: [Base = " + tri.dim1 + ", Height = " + tri.dim2 + "]");
        System.out.println("Computed Area = " + figRef.area() + " sq units
");

        // 3. Superclass reference pointing to generic Figure object
        figRef = genericFig;
        System.out.println("Generic Figure Area = " + figRef.area());
    }
}

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3. Sample Output

========================================
   DYNAMIC METHOD DISPATCH DEMO
========================================

Rectangle Dimensions: [Length = 12.0, Breadth = 8.0]
Calculating Area of Rectangle:
Computed Area = 96.0 sq units

Triangle Dimensions: [Base = 10.0, Height = 6.0]
Calculating Area of Triangle:
Computed Area = 30.0 sq units

Generic Figure Area = Area for generic Figure is undefined.
0.0

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4. Key OOP Concepts Demonstrated

1. Inheritance (extends & super): The subclasses inherit fields dim1 and dim2 and pass values using super(dim1, dim2).
2. Method Overriding (@Override): Subclasses provide specific implementations of the inherited area() method.
3. Runtime Polymorphism / Dynamic Method Dispatch: The Java Virtual Machine resolves the call figRef.area() dynamically at runtime based on the actual object type referenced by figRef, rather than the reference type.