Object-Oriented Programming (OOP)

OOP is a paradigm that organizes code into “objects” that contain data (attributes) and behaviors (methods).

The 4 Pillars of OOP

  1. Encapsulation: Hide internal details and expose only what’s needed (using private and getters/setters).
  2. Inheritance: Create new classes from existing ones (extends).
  3. Polymorphism: The ability of an object to behave in different ways.
  4. Abstraction: Represent complex concepts in a simplified way (abstract classes and interfaces).

Classes and Objects

  • Class: The blueprint or template (e.g., the Perro class).
  • Object: The actual instance created from the template (e.g., miPerro).
public class Perro {
    String nombre;
    
    public void ladrar() {
        System.out.println("¡Guau!");
    }
}

// Usage:
Perro miPerro = new Perro();
miPerro.nombre = "Firulais";
miPerro.ladrar();

Access Modifiers

  • public: Accessible from anywhere.
  • private: Only accessible within the same class.
  • protected: Accessible within the same package and by subclasses.
  • default: Only within the same package.

Constructors

Special methods that run when an object is created (new). They have no return type and are named the same as the class.

public Persona(String nombre, int edad) {
    this.nombre = nombre;
    this.edad = edad;
}

Wrappers

Classes that wrap primitive types to treat them as objects (e.g., Integer for int, Double for double). They are useful for collections.