0a1eeea424
* fix: replace sh with shell fix replace terminal with shell fix replace node with js fix replace output with shell fix replace cs with csharp fix replace c++ with cpp fix replace c# with csharp fix replace javasctipt with js fix replace syntax with js fix replace unix with shell fix replace linux with shell fix replace java 8 with java fix replace swift4 with swift fix replace react.js with jsx fix replace javascriot with js fix replace javacsript with js fix replace c++ - with cpp fix: corrected various typos fix: replace Algorithm with nothing fix: replace xaml with xml fix: replace solidity with nothing fix: replace c++ with cpp fix: replace txt with shell fix: replace code with json and css fix: replace console with shell
124 lines
3.4 KiB
Markdown
124 lines
3.4 KiB
Markdown
---
|
|
title: Class
|
|
---
|
|
|
|
## Class
|
|
|
|
A class in C# is defined as a reference type. In order to instantiate a variable of a reference type you must specify the `new` keyword, otherwise the variable will have the default value of `null`. See below for an example.
|
|
|
|
```csharp
|
|
// The value of variableOne is null at this point.
|
|
NewClass variableOne;
|
|
|
|
// Now the value of variableOne will be an instance of the class NewClass
|
|
variableOne = new NewClass();
|
|
```
|
|
|
|
At runtime, when the class is instantiated, enough memory is allocated onto the heap for that specific instance of the class held in the variable.
|
|
|
|
#### Creating Classes
|
|
To create a class in C# we need to use the `class` keyword followed by a unique identifier.
|
|
|
|
Like other languages, C# creates a default constructor that accepts no parameters. We can also specify our own constructor if we need to take in special parameters or have custom initialization steps in our constructor.
|
|
|
|
```csharp
|
|
public class NewClass
|
|
{
|
|
NewClass(string name)
|
|
{
|
|
// Initialization steps...
|
|
}
|
|
}
|
|
```
|
|
|
|
A class is a prototype or blueprint from which objects are created. In C#, the class is defined by using the keyword `class`. A class is used to combine together some methods, properties, fields, events, and delegates into a single unit. A class may contain nested classes too.
|
|
|
|
#### Example: Consider the case of Employee Class below:
|
|
```csharp
|
|
using System;
|
|
|
|
namespace CPrograms
|
|
{
|
|
class Employee
|
|
{
|
|
private string name;
|
|
private int employeeId;
|
|
|
|
public Employee(string name, int employeeId)
|
|
{
|
|
this.name = name;
|
|
this.employeeId = employeeId;
|
|
}
|
|
public void PrintEmployee()
|
|
{
|
|
Console.WriteLine("Employee Name: {0}, Employee ID: {1}", this.name, this.employeeId);
|
|
}
|
|
}
|
|
|
|
class Program
|
|
{
|
|
static void Main(string[] args)
|
|
{
|
|
Employee employeeObject = new Employee("John Doe", 420156);
|
|
employeeObject.PrintEmployee();
|
|
}
|
|
}
|
|
}
|
|
```
|
|
|
|
## Output:
|
|
```shell
|
|
> Employee Name: John Doe, Employee ID: 420156
|
|
```
|
|
|
|
A class can inherit from one base class only. However, it can implement from more than one interface.
|
|
|
|
#### Example of inheriting from one class and 2 interfaces
|
|
```csharp
|
|
// base class: Human
|
|
public class Human {
|
|
public int Age;
|
|
|
|
public Human (int age) {
|
|
Age = age;
|
|
}
|
|
}
|
|
|
|
// first interface: Student
|
|
public interface Student {
|
|
int StudentNumber { get; set; }
|
|
}
|
|
|
|
// second interface: Employee
|
|
public interface Employee {
|
|
int EmployeeNumber { get; set; }
|
|
string JobTitle { get; set; }
|
|
}
|
|
|
|
// Example of class extending a class and using 2 interfaces
|
|
public class Person : Human, Student, Employee {
|
|
// new field for Person
|
|
public string Name;
|
|
|
|
// needed to satisfy Student interface
|
|
public int StudentNumber { get; set; }
|
|
|
|
// needed to satisfy Employee interface
|
|
public int EmployeeNumber { get; set; }
|
|
public string JobTitle { get; set; }
|
|
|
|
// set the instance variables and pass the age to the base class
|
|
public Person(string name, int age, int studentNum, int employeeNum, string jobTitle) : base(age)
|
|
{
|
|
Name = name;
|
|
StudentNumber = studentNum;
|
|
EmployeeNumber = employeeNum;
|
|
JobTitle = jobTitle;
|
|
}
|
|
}
|
|
```
|
|
|
|
## More Information
|
|
Read more about classes [here](https://docs.microsoft.com/en-us/dotnet/csharp/language-reference/keywords/class)
|
|
|