1. Encapsulation
What it is: Encapsulation means bundling data and the methods that operate on that data into a single unit (class) and restricting direct access to some of the object’s internal state.
Why it matters:
- Protects data from unintended modification
- Improves maintainability and security
How it works:
- Use access modifiers (e.g.,
private,protected,public) - Expose data through methods (getters/setters)
Example (conceptual):
A BankAccount class hides the balance and only allows changes through deposit() or withdraw().
2. Inheritance
What it is: Inheritance allows a new class (child/subclass) to reuse and extend the behavior of an existing class (parent/superclass).
Why it matters:
- Promotes code reuse
- Establishes a clear “is-a” relationship
How it works:
- A child class inherits fields and methods from the parent
- The child can add new features or override existing ones
Example (conceptual):
A Car class inherits from a Vehicle class and adds car-specific behavior.
3. Polymorphism
What it is: Polymorphism means “many forms”—the same method name can behave differently depending on the object that calls it.
Why it matters:
- Makes code flexible and extensible
- Allows one interface to work with different implementations
How it works:
- Method overriding (runtime polymorphism)
- Method overloading (compile-time polymorphism, in some languages)
Example (conceptual):
A draw() method works differently for Circle, Rectangle, and Triangle objects.
4. Abstraction (often included as a main feature)
What it is: Abstraction focuses on what an object does rather than how it does it by exposing only essential features and hiding complex implementation details.
Why it matters:
- Reduces complexity
- Makes systems easier to understand and use
How it works:
- Abstract classes
- Interfaces
Example (conceptual):
A Payment interface defines pay(), while CreditCardPayment and PayPalPayment implement it differently.
One-Sentence Summary (Great for Exams)
- Encapsulation: Hides data and controls access through methods
- Inheritance: Allows a class to reuse and extend another class
- Polymorphism: Allows the same method to behave differently for different objects
- Abstraction: Shows only essential features and hides implementation details
TIPRefer to Week6 Lecture for more information.
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