Object-Oriented Programming (OOP)

Classes

• Blueprints for creating objects.

Abstract Classes

• The purpose is to provide a common definition of a base class that multiple derived classes can share;

• Allow to declare methods without implementation. These methods must be implemented in the child class;

• Abstract classes cannot be instantiated;

• Abstract classes must be extended.

Objects

• Instances of a class.

Interfaces

• A class can implement multiple interfaces;

• Interfaces contain only abstract methods (methods without implementation);

• Interfaces cannot contain attributes.

Inheritance

• A class can inherit attributes and methods from another class;

• The parent class is extended, and child class extends the parent;

• Private attributes and methods are not inherited;

• Specialization is achieved by extending a class. The extending class is called child;

• Generalization is achieved by combining classes into another one. The combined class is called parent.

Composition

• A class can contain objects of other classes as attributes.

• We can "inject" dependencies by requiring an argument as an instance of another class.

Encapsulation

• Set visibility to attributes & methods.

Abstraction

• Abstract classes cannot be instantiated.

• Abstract classes must be extended.

• Allow to declare methods without implementation. These methods must be implemented in the child class.

Polymorphism

• Change the behaviour of an extended class by overriding methods.