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 is necessary (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 (for example, the Dog class).
• Object: The real instance created from the template (for example, myDog).

public class Dog {
    String name;
    
    public void bark() {
        System.out.println("Woof!");
    }
}

// Usage:
Dog myDog = new Dog();
myDog.name = "Firulais";
myDog.bark();

Access Modifiers

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

Constructors

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

public Person(String name, int age) {
    this.name = name;
    this.age = age;
}

Wrappers

Classes that wrap primitive types so they can be treated as objects (for example, Integer for int, Double for double). They are useful for collections.