How do classes and objects interact in OOP?

In Object-Oriented Programming (OOP), classes define the properties and methods of objects, which are instances of these classes.

In more detail, a class in OOP is a blueprint or a template for creating objects. It defines a set of properties (also known as attributes or fields) and methods (also known as functions or behaviours) that an object of this class will have. For instance, if we have a class 'Car', it might have properties like 'colour', 'model', 'speed' and methods like 'accelerate', 'brake'.

An object, on the other hand, is an instance of a class. It is a specific representation of the class, with actual values assigned to the properties defined in the class. For example, a 'Car' object might have the colour 'red', model 'Ferrari', and speed '200 km/h'. It can also perform the methods defined in the class, such as accelerating or braking.

The interaction between classes and objects is fundamental to OOP. When a program is run, objects interact with each other by sending messages. When an object receives a message, it responds by executing one of its methods. This interaction is governed by the definitions in the class. For instance, if an object of the 'Car' class receives a 'brake' message, it will execute the 'brake' method defined in the 'Car' class.

Inheritance is another key aspect of the interaction between classes and objects in OOP. A class can inherit properties and methods from another class, known as its superclass. The inheriting class, known as the subclass, can then be used to create objects with the inherited properties and methods, as well as any additional ones defined in the subclass. This allows for code reusability and a hierarchical organisation of classes and objects.

In summary, classes and objects interact in OOP through the definitions in the class, which determine the properties and methods of the objects, and through the messages that objects send to each other, which trigger the execution of methods. Inheritance also plays a crucial role in this interaction, allowing classes and objects to be organised hierarchically and code to be reused.