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Constructor plays a very important role in Object-Oriented Programming. Let us understand the role of constructor in C# with the help of the following points:
Syntax:
public class Student() { //constructor public Student() { //code } }
Here, public Student() is a method that does not have any return type, not even void, and its name is the same as the class name, i.e. ‘Student’. Thus, this method is the constructor of this class.
When we create an object of this class using:
Student obj = new Student();
Then the code inside the constructor will be executed.
1. The constructor initializes data members for the new object. It is invoked by the ‘new’ operator immediately after memory gets allocated to the new object.
2. Explicit constructors (constructors defined by the user) can be parameterless or parameterized. If it is parameterized, then the values passed to the constructor can be assigned to the class’s data members.
3. The implicit constructor initializes variables of the class with the same value even if we create multiple instances of that class.
Example:
Code:
using System; public class ConstructorDemo { public int num = 10; public static void Main() { ConstructorDemo obj1 = new ConstructorDemo(); ConstructorDemo obj2 = new ConstructorDemo(); ConstructorDemo obj3 = new ConstructorDemo(); Console.WriteLine("obj1.num = "+obj1.num+"\nobj2.num = "+obj2.num +"\nobj3.num = "+obj3.num); } }
Output:
Pictorial Representation of Above Program:
4. Explicit constructor with parameters allows us to initialize variables of the class with a different value each time we create an instance of that class.
Example:
Code:
using System; public class ConstructorDemo { public int num; //explicit constructor public ConstructorDemo(int num) { this.num = num; } public static void Main() { ConstructorDemo obj1 = new ConstructorDemo(10); ConstructorDemo obj2 = new ConstructorDemo(20); ConstructorDemo obj3 = new ConstructorDemo(30); Console.WriteLine("obj1.num = "+obj1.num+"\nobj2.num = "+obj2.num +"\nobj3.num = "+obj3.num); } }
Output:
Pictorial Representation of Above Program:
C# provides five types of constructors. They are as follows:
Example:
Code:
using System; public class DefaultConstructor { public int num; public string str; } public class Demo { public static void Main() { DefaultConstructor obj = new DefaultConstructor(); Console.WriteLine("obj.num = "+obj.num+"\nobj.str = "+obj.str); } }
Output:
A constructor with at least one parameter is called Parameterized Constructor. Parameters to the constructor can be passed while creating the instance of the class. It allows us to initialize each instance of a class with different values.
Example:
Code:
using System; public class ParameterizedConstructor { public int num; public string str; //parameterized constructor public ParameterizedConstructor(int num, string str) { this.num = num; this.str = str; } } public class Demo { public static void Main() { //passing values to constructor while creating instance ParameterizedConstructor obj = new ParameterizedConstructor(50, "constructor"); Console.WriteLine("obj.num = "+obj.num+"\nobj.str = "+obj.str); } }
Output:
It is a parameterized constructor that takes the same class’s object as a parameter. It copies the existing object’s value (which is passed as a parameter) to the newly created object instantiated by the constructor. We can say that it copies data of one object to another object.
Example:
Code:
using System; public class CopyConstructor { public int num; public CopyConstructor(int num) { this.num = num; } //copy constructor public CopyConstructor(CopyConstructor obj) { num = obj.num; } } public class Demo { public static void Main() { CopyConstructor obj1 = new CopyConstructor(50); //passing same class's object as parameter CopyConstructor obj2 = new CopyConstructor(obj1); Console.WriteLine("Original object:"); Console.WriteLine("obj1.num = "+obj1.num); Console.WriteLine("\nCopied object:"); Console.WriteLine("obj2.num = "+obj2.num); } }
Output:
Example:
Code:
using System; public class StaticConstructor { //static constructor static StaticConstructor() { Console.WriteLine("Static constructor executed"); } public static void Display() { Console.WriteLine("\nDisplay method executed"); } } public class Demo { public static void Main() { StaticConstructor.Display(); } }
Output:
A constructor created with a private specifier is called a private constructor. We cannot create an instance of the class if it contains only a private constructor, and it does not allow other classes to derive from this class. Used in class that contains only static members.
Example:
Code:
using System; public class PrivateConstructor { public static int num = 100; //private constructor private PrivateConstructor() { } } public class Demo { public static void Main() { //PrivateConstructor obj = new PrivateConstructor(); //Error Console.WriteLine("num = "+PrivateConstructor.num); } }
Output:
If we define any type of constructor in a class, then there will not be any implicit constructor in the class provided by the compiler. Like methods, parameterized constructors can also be overloaded with different numbers of parameters. Constructors defined implicitly by the compiler are always public.
This is a guide to Constructor in C#. Here we discuss the types of Constructor in C# and its Work along with Code Implementation and Output. You can also go through our other suggested articles to learn more –
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