Inheritance

In OOP, inheritance is a mechanism where a new class, known as a subclass, derives properties and behaviors from an existing class, termed as a superclass. This relationship is often described as "is a kind of", indicating that the subclass is a specific type of the superclass.

Java Examples of Inheritance

Consider the concept of shapes in geometry. We can define a generic class Shape with common properties and methods relevant to all shapes. Subclasses like Circle and Rectangle can then inherit from Shape, as illustrated in the following Java examples:

public abstract class Shape {
  public abstract double area();
  public abstract double circumference();
}

class Circle extends Shape {
  public static final double PI = 3.14159265358979323846;
  protected double r;

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

  public double area() {
    return PI * r * r;
  }

  public double circumference() {
    return 2 * PI * r;
  }
}

class Rectangle extends Shape {
  protected double width, height;

  public Rectangle(double width, double height) {
    this.width = width;
    this.height = height;
  }

  public double area() {
    return width * height;
  }

  public double circumference() {
    return 2 * (width + height);
  }
}

Advantages and Appropriate Use of Inheritance

Inheritance creates a structured, hierarchical organization of classes, effectively modeling the complexity of many real-world scenarios that naturally exhibit hierarchical relationships. It facilitates code reuse by allowing common attributes and behaviors to be defined once in the superclass, eliminating the need for repetition in each subclass.

However, it's crucial to apply inheritance judiciously. It should be employed when there is a genuine "is a kind of" relationship and not merely to reuse code. Overuse or misuse of inheritance can lead to unnecessarily complicated class hierarchies and maintenance challenges.

Object Composition as an Alternative

For scenarios where code reuse is desired without establishing an "is a kind of" relationship, object composition offers a robust alternative. This approach involves building complex objects by combining simpler ones. For instance, combining a Cooktop and an Oven can create a Stove. This method provides flexibility and fosters a more modular design, adhering to the principle of composition over inheritance.