Constructor in C#

A constructor is a special method in C# that is used to initialize an object of a class. It is called automatically when an object is created, and its primary purpose is to set the initial values of the object’s properties.

Here is an example of a constructor in C#:

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string Gender { get; set; }

    public Person(string name, int age, string gender)
    {
        Name = name;
        Age = age;
        Gender = gender;
    }
}

In this example, we have defined a constructor for the Person class that takes three parameters: name, age, and gender. When an object of the Person class is created, the constructor will automatically be called and the object’s Name, Age, and Gender properties will be initialized with the values passed to the constructor.

Here is an example of how to create an object of the Person class using the constructor:

Person person1 = new Person("John", 30, "Male");

In this example, we have created an object of the Person class named person1 and passed in the values “John”, 30, and “Male” to the constructor. These values will be used to initialize the object’s properties.

Rules for constructors in C#:

1. The constructor must have the same name as the class it belongs to.
2. The constructor can have parameters, but it is not required to have any.
3. If a class does not have any constructors defined, a default constructor will be generated automatically. The default constructor takes no parameters and does not initialize any properties.
4. A class can have multiple constructors with different parameter lists. This is known as constructor overloading.
5. Constructors can call other constructors in the same class using the this keyword. This is known as constructor chaining.

Here is an example of constructor overloading and constructor chaining:

public class Person
{
    public string Name { get; set; }
    public int Age { get; set; }
    public string Gender { get; set; }

    public Person(string name, int age, string gender)
    {
        Name = name;
        Age = age;
        Gender = gender;
    }

    public Person(string name) : this(name, 0, "Unknown")
    {
    }
}

In this example, we have defined two constructors for the Person class: one that takes three parameters and another that takes only one parameter. The second constructor calls the first constructor using the this keyword, passing in the name parameter and default values for age and gender.

Here is an example of how to create an object of the Person class using the second constructor:

Person person2 = new Person("Jane");

In this example, we have created an object of the Person class named person2 using the second constructor, which only takes the name parameter. Since the age and gender parameters are not specified, their default values will be used.

6. Constructors can also call constructors of the base class using the base keyword. This is known as base constructor chaining.

Here is an example of using the base keyword to call the constructor of the base class:

public class Student : Person
{
    public int Grade { get; set; }

    public Student(string name, int age, string gender, int grade) : base(name, age, gender)
    {
        Grade = grade;
    }
}

In this example, we have defined a Student class that inherits from the Person class. The Student class has an additional Grade property. The constructor of the Student class calls the constructor of the base Person class using the base keyword, passing in the name, age, and gender parameters. The Grade property is initialized with the value passed in to the constructor.

Here is an example of how to create an object of the Student class:

Student student1 = new Student("Mary", 18, "Female", 12);

In this example, we have created an object of the Student class named student1 and passed in the values “Mary”, 18, “Female”, and 12 to the constructor. The Student class constructor calls the base Person class constructor to initialize the Name, Age, and Gender properties, and then initializes the Grade property with the value 12.

In summary, a constructor is a special method in C# that is used to initialize an object of a class. It is called automatically when an object is created and its primary purpose is to set the initial values of the object’s properties. The rules for constructors in C# include having the same name as the class, being able to have parameters, generating a default constructor if none is defined, allowing for constructor overloading and chaining, and being able to call the base class constructor using the base keyword.