What is boxing and unboxing in c# .net ?

C# Type System contains three Types , they are Value Types , Reference Types and Pointer Types. C# allows us to convert a Value Type to a Reference Type, and back again to Value Types . The operation of Converting a Value Type to a Reference Type is called Boxing and the reverse operation is called Unboxing.

Boxing is the process of converting a value type to the type object or to any interface type implemented by this value type. When the CLR boxes a value type, it wraps the value inside a System.Object and stores it on the managed heap. Unboxing extracts the value type from the object.

Boxing using code:-

•   int Val = 1;
•   Object Obj = Val;   //Boxing

The first line we created a Value Type Val and assigned a value to Val. The second line , we created an instance of Object Obj and assign the value of Val to Obj. From the above operation (Object Obj = i ) we saw converting a value of a Value Type into a value of a corresponding Reference Type . These types of operation is called Boxing.

UnBoxing using code:-

• int Val = 1;
• Object Obj = Val;        //Boxing
• int i = (int)Obj;            //Unboxing

The first two line shows how to Box a Value Type . The next line (int i = (int) Obj) shows extracts the Value Type from the Object . That is converting a value of a Reference Type into a value of a Value Type. This operation is called UnBoxing.

Boxing and UnBoxing are computationally expensive processes. When a value type is boxed, an entirely new object must be allocated and constructed , also the cast required for UnBoxing is also expensive computationally.


Source code example:-

using System;

using System.Collections.Generic;

using System.Linq;

using System.Text;

using System.Threading.Tasks;

namespace ConsoleDemoApp

{

    class Test

    {

        static void Main(string[] args)

        {

            Console.WriteLine("\n");

            Console.WriteLine("Enter a Integer value");

            int value = Convert.ToInt32(Console.ReadLine());

            //Boxing implicit conversion

            Object Obj = value;

            Console.WriteLine("Boxing(Object/Boxed Value) : {0}\n", Obj.ToString());

            //Unboxing explicit conversion

            int num = (int)Obj;

            Console.WriteLine("UnBoxing(Entered Number Value): {0}\n", num);

            Console.ReadKey();

        }

    }

}

  

Output:-