What is the purpose of classes in PHP?

In PHP, a class is a blueprint or template used to define objects. It defines the properties (member variables) and methods (member functions) of an object, and can be used to create objects. Classes allow related data and methods to be grouped together, enabling encapsulation and code reuse. The main purposes of classes include:

1. Encapsulation: Classes encapsulate data (attributes) and behavior (methods) together, achieving data hiding and protection. Only through the class’s public interface can data be accessed and operated on, improving code security and maintainability.
2. Inheritance: Classes can create derived subclasses through inheritance, where the subclass inherits the properties and methods of the parent class, and can also add its own properties and methods, enabling code reuse and expansion.
3. Polymorphism: The inheritance and interface implementation mechanisms of classes allow objects of different classes to be treated as the same type, thereby achieving polymorphism. This enables the dynamic invocation of corresponding methods at runtime based on the actual type of the object, enhancing the flexibility and scalability of the code.

In conclusion, classes are the fundamental building blocks of object-oriented programming (OOP), allowing for encapsulation, inheritance, and polymorphism, which improve code modularization, maintainability, and reusability.