What is the difference between implements and extends in PHP ?

PHP facilitates two keywords, i.e. the implements and extends keywords, which can be used in the context of class inheritance and interface implementation. While both keywords are related to the concept of Object-Oriented Programming, they serve different purposes.

Extends Keyword

The extends keyword is used to create a subclass that inherits from another class. Inheritance is a fundamental concept in object-oriented programming, allowing a class to inherit the properties and methods of another class.

Syntax

class First {
    public function parent() {
        // Code...
    }
}
class Second extends First {
      // Code...
}

Example: Implementation of extend keyword in PHP.

PHP

<?php

class ParentClass
{
    public function parentMethod()
    {
        echo "This is a method from the parent class.\n";
    }
}

class ChildClass extends ParentClass
{
    public function childMethod()
    {
        echo "This is a method from the child class.\n";
    }
}

$childObj = new ChildClass();
$childObj->parentMethod();
$childObj->childMethod();

?>

Output

This is a method from the parent class.
This is a method from the child class.

Implements Keyword

The implements keyword is used to declare that a class implements one or more interfaces. An interface defines a contract that implementing classes must adhere to, specifying a set of methods that the class must implement.

Syntax

interface MyInterface
{
    // Method...
}

class MyClass implements MyInterface
{
   // Method...
}

Example: Implementation of implements keyword in PHP.

PHP

<?php

interface MyInterface
{
    public function interfaceMethod();
}

class MyClass implements MyInterface
{
    public function interfaceMethod()
    {
        echo "This is the implementation of the interface method.\n";
    }
}

$obj = new MyClass();
$obj->interfaceMethod();

?>

Output

This is the implementation of the interface method.

Differences Between Implements and Extends

Now, let’s summarize the key differences between implements and extends:

Parameters	Implements	Extends
Purpose	Implements interfaces	Extends a class
Syntax	class MyClass implements MyInterface	class ChildClass extends ParentClass
Inheritance	No inheritance from the interface	Inheriting properties and methods from the parent class
Multiple Usage	Can implement multiple interfaces	Can only extend one class
Abstract Classes	Can implement abstract classes	Can only extend concrete (non-abstract) classes
Code Reusability	Promotes code reusability through interface implementation	Promotes code reusability through class inheritance