Objects and classes in C#

Objects and classes are fundamental concepts in C# and object-oriented programming. This concise Answer provides an overview of objects and classes in C#, highlighting their significance. Understanding the relationship between objects and classes is essential for building modular and extensible software systems in C#.

Classes in C#

A class in C# is a blueprint or template specifying objects' composition, conduct, and attributes. It is a model for making numerous objects with comparable features and operations. A class is a logical container for associated information and functions—a blueprint for making things. A class-based object is essentially an instance built according to the class’s blueprint when it is created.

Class structure

The following components make up a class in C#.

Fields: They are class-specific variables that store data or state. They stand in for the traits or qualities of objects derived from the class.
Properties: Properties offer restricted access to a class’s fields. They contain the fields and let you specify logic or validation for getting or setting the data.
Methods: Within a class, a method is a function that specifies the behavior or operations that an object is capable of. They contain the activities or features related to the class.

Fundamental concepts in class

There are three fundamental conceptions associated with classes in object-oriented programming.

Encapsulation: It is the process of grouping data and methods within a class, concealing internal implementation details, and enhancing data security and code maintainability.
Inheritance: For code reuse, modularity, and extensibility, inheritance refers to a class that derives its characteristics and behavior from a base or parent class.
Polymorphism: When objects of several classes are treated as instances of a single base class, polymorphism is supported, providing flexibility, interchangeability, and method overriding and overloading.

Access modifiers in C#

Access modifiers in C# control the accessibility of class members (fields, properties, methods).

Public: Accessible from any part of the code.
Private: Accessible only within the same class.
Protected: Accessible within the same class and derived classes.
Internal: Accessible within the same assembly.
Protected Internal: Accessible within the same assembly and derived classes.

These modifiers help enforce encapsulation and define the visibility of members, allowing you to control how other parts of your code access them.

Objects in C#

An object in C# is a particular instance of a class. It represents a real-world or abstract thing your program can work with and manipulate. Objects have a distinct identity, may store data (state), and can act in ways specified by their class (behavior).

Objects as instances of classes

Based on class definitions, objects are formed. A class is a template specifying an object's characteristics, behaviors, and structure. You can make an object with all the features a class lists by instantiating it. A class can produce several objects with unique identities and states.

Characteristics of objects

State and behavior are the two main features of objects in C#.

The data or variables connected to an item are called its state. It represents the current values or properties of the object, which are accessible and modifiable.
An object’s behavior is defined as the activities or operations it is capable of. These actions can be used on an item to change its state or communicate with other objects and are often described as methods inside the class.

Using the `new` keyword to create objects

When creating an object in C#, the new keyword is used, then the class name and brackets. This action is referred to as instantiation. The class's constructora special method within a class that is automatically called when an object is created, used to initialize the object's state. method is called to initialize the object’s initial state if defined. The memory is allocated to keep it when an object is formed. The object is made available in your program using the new keyword, which guarantees that the required memory has been allocated.

Relationship between class and objects in C#

Class and objects have a very close relationship. This can be explained with the help of an example.

The Person class in the example below represents a person with name and age properties. Two objects person1 and person2, are created from the Person class using the new keyword. Each object has its state (name and age) and can invoke the DisplayInfo method to display its information.

using System;
namespace YourNamespace
{
    class Person
    {
        public string Name;
        public int Age;
        
        public void DisplayInfo()
        {
            Console.WriteLine("Name: " + Name);
            Console.WriteLine("Age: " + Age);
        }
    }
    
    class Program
    {
        static void Main(string[] args)
        {
            Person person1 = new Person();
            person1.Name = "John";
            person1.Age = 25;
            
            Person person2 = new Person();
            person2.Name = "Alice";
            person2.Age = 30;
            
            person1.DisplayInfo();
            person2.DisplayInfo();
        }
    }
}