Object-Oriented Programming
Learn why OOP exists before you learn its four keywords
6 lessons · 1.2 hours of reading
· Beginner · 3 free
Classes, encapsulation, inheritance, polymorphism and SOLID, taught in Java with programs you can compile and run. Every idea starts from the problem it was invented to solve.
Lessons
1
What a class models, and why OOP was invented
The problem parallel arrays create, and how bundling data with behaviour fixes it.
2
Encapsulation, and why getters exist
Private fields are not ceremony; they are how you make invalid states impossible.
3
Inheritance, and when NOT to use it
How extends works, plus a runnable example of the classic case where inheritance is the wrong tool.
4
Polymorphism, with a runnable example
One loop that handles types it has never heard of, and the difference between overloading and overriding.
5
Abstraction: interfaces versus abstract classes
What each one is for, when to pick which, and a program using both together.
6
The SOLID principles in plain English
Five design rules, each with the smell it fixes and a short Java example.
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