Object-Oriented PHP
PHP's object-oriented features have grown from minimal in PHP 4 to a full modern OOP system in PHP 8+. Object-oriented programming (OOP) organizes code into classes with data (properties) and behaviour (methods), enabling encapsulation, inheritance, and polymorphism.
Classes and Objects
A class is declared with class Name { ... }. Properties and methods may be public, protected, or private. Objects are instantiated with new Name(). The constructor __construct initializes state. Property promotion in PHP 8 lets constructor parameters be promoted to typed properties in one line.
Encapsulation
Encapsulation keeps internal data private and exposes only controlled interfaces. Public getters and setters, or readonly properties (PHP 8.1+), let callers interact safely. This separates interface from implementation and allows later refactoring.
Inheritance
A class may extends another, inheriting its public and protected members. Child classes can override parent methods and access them via parent::method(). PHP supports single inheritance only. Overuse of inheritance produces brittle hierarchies; composition often works better.
Abstract Classes and Interfaces
Abstract classes cannot be instantiated and can declare abstract methods without implementation. Interfaces (declared with interface) are pure contracts — a list of method signatures a class must implement. A class can implement many interfaces. Interfaces support polymorphism and dependency inversion.
Traits
Traits are reusable fragments of class code that side-step single-inheritance limits. A class uses a trait to inherit its methods and properties. Traits support horizontal code reuse but should be used sparingly to avoid confusion.
Static Members
Static properties and methods belong to the class, not instances, and are accessed via ::. Static factories and utility functions are common uses. Overusing statics creates hidden dependencies and complicates testing.
Namespaces and Autoloading
Namespaces (declared with namespace) organize classes and prevent name collisions across libraries. PSR-4 autoloading with Composer maps namespaces to directory structures, loading classes on demand. Modern PHP projects are structured around namespaces.
Magic Methods
PHP provides magic methods like __toString, __get, __set, __call, __invoke, and __clone that let objects customize built-in behaviour. They enable fluent APIs and proxy patterns but can obscure code.
Dependency Injection
Dependency injection (DI) hands a class its collaborators rather than letting it create them. DI improves testability and flexibility. Frameworks like Symfony and Laravel provide DI containers to manage object wiring.
Design Patterns
Common patterns such as Singleton, Factory, Repository, Strategy, and Observer recur in PHP code. Familiarity with these patterns speeds reading third-party code and helps structure your own.
Summary
Object-oriented PHP gives you classes, inheritance, interfaces, traits, namespaces, and DI. Used judiciously, OOP produces maintainable, testable applications. Modern frameworks and libraries rely heavily on these features; mastering them is essential for professional PHP development.