What are the best practices for working with multiple classes in PHP, including the use of instantiation within classes?

When working with multiple classes in PHP, it is best practice to use instantiation within classes to create objects of other classes as needed. This helps to encapsulate functionality, improve code organization, and promote reusability. To instantiate a class within another class, you can simply create a new object of the desired class within the constructor or method of the parent class.

<?php

class ClassA {
    public function __construct() {
        // Instantiate ClassB within ClassA
        $classB = new ClassB();
        $classB->someMethod();
    }
}

class ClassB {
    public function someMethod() {
        // Method implementation
    }
}

// Create an object of ClassA to trigger instantiation of ClassB
$classA = new ClassA();

?>