Abstracts, Final, Interface, and Trait Class

December 18, 2023 (1y ago)

If you've been actively engaging with PHP, you've likely encountered Final, Interfaces, Traits, and Abstract classes. Initially, these constructs may seem somewhat similar, making it challenging to discern their distinctions and optimal use cases. By the conclusion of this article, you'll gain a clear understanding of their unique features, enabling you to confidently choose the most suitable option for a given scenario.

Abstract Class

An abstract class closely resembles a regular class but includes abstract methods. Unlike an ordinary class, it cannot be instantiated independently. Abstract classes serve as excellent templates for classes that are expected to have a shared ancestor.

Consider, for instance, classes such as Cat and Dog. These classes may share certain methods and functionalities. Creating a parent abstract class becomes beneficial in this scenario, allowing for the inclusion of shared methods while mandating the implementation of specific methods in the child classes. This ensures a structured and cohesive design for related classes.


abstract class Animal {
    public function eat() {
        echo "The animal is eating.";

    abstract public function makeSound();

class Cat extends Animal {
    public function makeSound() {
        echo "Meow!";

class Dog extends Animal {
    public function makeSound() {
        echo "Woof!";

$cat = new Cat();
$dog = new Dog();



Some takeaways about abstract classes:

  • Can't be instantiated on their own
  • Abstract methods just declare a signature and no functionality
  • Used by a child class with extends keyword
  • Act as a sort of partially-built class

Interface Class

Interfaces serve as a mechanism to mandate particular implementations in classes that adopt them. These constructs exclusively consist of method signatures, devoid of any actual functionality. Their primary purpose is to establish a standardized structure and function as templates for constructing classes, emphasizing adherence to a predefined set of methods.


// Interface
interface Shape {
    public function calculateArea();

// Class implementing the interface
class Circle implements Shape {
    private $radius;

    public function __construct($radius) {
        $this->radius = $radius;

    // Implementation of the interface method
    public function calculateArea() {
        return pi() * $this->radius * $this->radius;

// Class using the interface
class Square implements Shape {
    private $side;

    public function __construct($side) {
        $this->side = $side;

    // Implementation of the interface method
    public function calculateArea() {
        return $this->side * $this->side;

// Usage
$circle = new Circle(5);
$square = new Square(4);

echo "Circle Area: " . $circle->calculateArea();
echo "Square Area: " . $square->calculateArea();

Some takeaways about interfaces:

  • Act as blueprints for classes
  • Used in the class declaration with implements keyword
  • Multiple can be used in the same class
  • Can only contain method signatures and no properties

Final Class

A final class is a class that cannot be extended or subclassed. When a class is declared as final, it means that it is considered complete and should not be further modified or specialized by creating derived classes. This restriction is enforced by the language, and any attempt to extend a final class will result in a compilation or runtime error.


// Final Class
final class FinalClass {
    public function hello() {
        echo "Hello from FinalClass!";

// Attempting to extend a final class will result in an error
class ExtendedClass extends FinalClass {
    // Error: Class ExtendedClass may not inherit from final class (FinalClass)

// Creating an instance of the final class
$finalInstance = new FinalClass();

Trait Class

Traits provide a mechanism for code reuse across multiple classes, even when these classes are not inherently related. In contrast to abstract classes, a single class can incorporate multiple traits using the use statement.

Traits are often employed to consolidate somewhat related methods and properties, seamlessly integrating additional functionality into the classes that utilize them. This flexibility allows developers to compose classes with a mix-and-match approach, bringing together diverse traits to meet specific needs.


// Trait
trait Logging {
    public function logMessage($message) {
        echo "Logging: $message";

// Class using the trait
class User {
    use Logging;

    public function performAction() {
        // Using the method from the trait
        $this->logMessage("Performed an action.");
        // Additional class-specific functionality

// Creating an instance of the class
$user = new User();
$user->performAction();  // Outputs: Logging: Performed an action.

Some takeaways about traits:

  • Perfect for code reuse
  • Implemented in the class body with use keyword
  • Multiple can be used in the same class
  • Can have both properties and methods


In conclusion, understanding the distinctions and applications of abstract classes, interfaces, and traits in PHP is essential for designing flexible and maintainable object-oriented code. Abstract classes serve as blueprints with shared functionality and enforced method implementations in subclasses. Interfaces define method contracts, ensuring adherence to a specific structure across diverse classes. Traits offer a unique way to reuse code in unrelated classes, allowing a class to incorporate multiple traits and tailor its functionality dynamically. The judicious use of these constructs empowers developers to create well-organized, extensible, and modular code, fostering a robust and scalable software architecture.