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Introduction to Object-Oriented Programming (OOP)

OOP is a programming paradigm that uses "objects" – instances of classes – which are capable of holding data in the form of fields (also known as properties or attributes) and methods. OOP focuses on the objects that developers want to manipulate rather than the logic required to manipulate them.

There are four primary principles of OOP:

  1. Encapsulation: This is the practice of keeping fields within a class private, then providing access to them via public methods. It’s a protective barrier that keeps the data and code safe within the class itself.

  2. Inheritance: This is the process where one class adopts the properties (fields) and methods of another. With inheritance, we can reuse the code, making the program easier to develop and understand.

  3. Polymorphism: This allows us to perform a single action in different ways. Polymorphism allows us to define one interface and have multiple implementations.

  4. Abstraction: This is a process of hiding the implementation details and showing only the functionality to the users. Abstraction lets us focus on what the object does instead of how it does it.

Understanding and applying these principles will allow you to write more efficient, effective, and manageable code.

Why OOP is Useful in Programming

OOP provides a clear structure for the programs. OOP helps to keep the Java code DRY (Don't Repeat Yourself), which makes the code easier to maintain, modify and debug. It also makes it possible to create full reusable applications with less code and shorter development time.

Object-oriented Programming in 7 minutes | Mosh (YouTube)


To test your understanding of OOP principles, your task for this week is to answer the following questions:

  1. What are the main principles of Object-Oriented Programming and how would you describe each one in your own words?
  2. Why are these principles important and how do they make programming easier or more effective?
  3. Can you think of a real-world analogy for each of the four principles? For example, a Library could be an analogy for encapsulation, as it keeps the books (data) protected and organized, and provides a specific interface (librarian/methods) to access them.