Introspection is the ability of a program to examine an object’s characteristics, such as its name, parent class (if any), properties, and methods. With introspection, you can write code that operates on any class or object. You don’t need to know which methods or properties are defined when you write your code; instead, you can discover that information at runtime, which makes it possible for you to write generic debuggers, serializers, profilers, etc
Examining Classes
To determine whether a class exists, use the class_exists() function, which takes in a string and returns a Boolean value. Alternately, you can use the get_ declared_classes() function, which returns an array of defined classes and checks if the class name is in the returned array:
$doesClassExist = class_exists(classname);
$classes = get_declared_classes();
$doesClassExist = in_array(classname, $classes);