Boxing is used to store value types in the garbage-collected heap. Boxing is an implicit conversion of a value type to the type object or to any interface type implemented by this value type. Boxing a value type allocates an object instance on the heap and copies the value into the new object.

Consider the following declaration of a value-type variable:

int i = 123;

The following statement implicitly applies the boxing operation on the variable i:

// Boxing copies the value of i into object o. object o = i;  

The result of this statement is creating an object reference o, on the stack, that references a value of the type int, on the heap. This value is a copy of the value-type value assigned to the variable

for example:(Consider follwing C# code)

class TestBoxing
{
static void Main()
{
int i = 123;
// Boxing copies the value of i into object o. object o = i;  
// Change the value of i.
i = 456;  
// The change in i does not effect the value stored in o.
System.Console.WriteLine("The value-type value = {0}", i);
System.Console.WriteLine("The object-type value = {0}", o);
}
}
/* Output:
The value-type value = 456
The object-type value = 123
*/

Unboxing