C Sharp

Objects vs. Classes

The difference between a class and an object is a source of confusion for programmers new to the terminology of object-oriented programming. To illustrate the difference between these two terms, let's make our EmployeeApp example more realistic by assuming that we're working not with a single employee but with an entire company of employees.

Using the C language, we could define an array of employees-based on the EMPLOYEE structure-and start from there. Because we don't know how many employees our company might one day employ, we could create this array with a static number of elements, such as 10,000. However, given that our company currently has only Amy as its sole employee, this wouldn't exactly be the most efficient use of resources. Instead, we would normally create a linked list of EMPLOYEE structures and dynamically allocate memory as needed in our new payroll application.

My point is that we're doing exactly what we shouldn't be doing. We're expending mental energy thinking about the language and the machine-in terms of how much memory to allocate and when to allocate it-instead of concentrating on the problem domain. Using objects, we can focus on the business logic instead of the machinery needed to solve the problem.

There are many ways to define a class and distinguish it from an object. You can think of a class as simply a type (just like char, int, or long) that has methods associated with it. An object is an instance of a type or class. However, the definition I like best is that a class is a blueprint for an object. You, as the developer, create this blueprint as an engineer would create the blueprint of a house. Once the blueprint is complete, you have only one blueprint for any given type of house.

However, any number of people can purchase the blueprint and have the same house built. By the same token, a class is a blueprint for a given set of functionality, and an object created based on a particular class has all the functionality of the class built right in.

by BrainBellupdated
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