Question:

Consider the following classes in Java:

public class Rectangle {
    private int width;
    private int height;
    
    public Rectangle(int width, int height) {
        this.width = width;
        this.height = height;
    }
    
    public int getArea() {
        return width * height;
    }
    
    public void setWidth(int width) {
        this.width = width;
    }
    
    public void setHeight(int height) {
        this.height = height;
    }
}

public class Square extends Rectangle {
    public Square(int sideLength) {
        super(sideLength, sideLength);
    }
    
    public void setSideLength(int sideLength) {
        setWidth(sideLength);
        setHeight(sideLength);
    }
}

Explain whether the class hierarchy demonstrated in the code snippet above adheres to the principles of Object-Oriented Programming (OOP). Analyze its design, inheritance, and relationships between classes.

Answer:

The class hierarchy demonstrated in the code snippet adheres to the principles of Object-Oriented Programming (OOP). Here's a detailed analysis of its design, inheritance, and relationships between classes:

1. Design:

The design of the classes Rectangle and Square follows the principle of encapsulation by declaring the width and height fields as private and providing public methods to access and modify these fields.

The Rectangle class has a constructor method that accepts the width and height as parameters and initializes the corresponding fields.

The Rectangle class also has a getArea method, which calculates and returns the area of the rectangle based on its width and height.

The Square class is a subclass of Rectangle and inherits its fields and methods. It adds an additional method setSideLength specific to a square.

2. Inheritance:

The Square class inherits from the Rectangle class using the extends keyword. This relationship represents the "is-a" relationship between a square and a rectangle - a square is a specific type of rectangle where all sides are equal.

The Square class overrides the setWidth and setHeight methods inherited from the Rectangle class in order to maintain the square's invariant (all sides are equal). It accomplishes this by setting both the width and height to the given value in the setSideLength method.

Note that the Square class does not declare any new fields or methods. It inherits them from the Rectangle class.

3. Relationships:

The relationship between the Rectangle and Square classes can be described as superclass-subclass relationship or parent-child relationship. The Square class is a specialized version of the Rectangle class, inheriting its properties and behaviors.

The Square class utilizes the methods from the Rectangle class to set the width and height, maintaining the square's invariant. This relationship demonstrates the principle of code reuse, as the Square class can use the existing methods from the Rectangle class without having to implement them again.

Overall, the class hierarchy demonstrated in the code snippet follows the principles of OOP by encapsulating data, utilizing inheritance, and establishing relationships between classes to model real-world concepts.