Object-Oriented Programming

State + Behavior · The Four Pillars

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The four pillars of OOP — encapsulation, abstraction, inheritance, and polymorphism — and when to use composition instead.

By the end, you can

Explain what an object is and distinguish its state from its behavior.
Describe the relationship between a class and its instances, and state what the constructor does.
Define each of the four pillars and give a concrete example of each.
Distinguish encapsulation (hiding state) from abstraction (hiding complexity).
Distinguish method overriding (dynamic dispatch, runtime) from method overloading (compile time).
Identify whether a relationship calls for inheritance (is-a) or composition (has-a).
Explain the fragile base class problem and why composition is usually preferred over deep inheritance.

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