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Exercise

Square and rectangle

The classic example of a problem that violates the Liskov Substitution Principle is the Circle-Ellipse problem, sometimes called the Square-Rectangle problem.

By all means, it seems like you should be able to define a class Rectangle, with attributes h and w (for height and width), and then define a class Square that inherits from the Rectangle. After all, a square "is-a" rectangle!

Unfortunately, this intuition doesn't apply to object-oriented design.

Instructions 1/4
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  • Create a class Rectangle with a constructor that accepts two parameters, h and w, and sets its h and w attributes to the values of h and w.
  • Create a class Square inherited from Rectangle with a constructor that accepts one parameter w, and sets both the h and w attributes to the value of w.