BOXING AND UNBOXING IN C# Articles, samples and tutorials

BOXING AND UNBOXING IN C#

Boxing refers to the conversion of a value type into a reference type whereas Unboxing means converting a reference type into a value type.These are very powerful features of C# .With boxing,you can manipulate complex reference type in the way that you would manipulate simple value types.This plays an important role in implementing polymorphism.

The following example depicted below in order to understand the concept of boxing and unboxing clearly.

...
class BoxMe
{
int iTakeObjs(object x)
}
//iTakeObjs takes an object
//and processes it here
}

object iSpitObjs()
{
//ispitObjs does the processing
//and returns an object
}
}
...

//Implementation of code
int v;
v=5;
BoxMe up = new BoxMe();
up.TakeObjs(v);
//BookMark 1

int unBox = (int) up.iSpitObjs();
//bookmark 2
...

In the example above,a class having two methods has been defined.The First method,iTakeObjs() takes in an object as a parameter.The second method
iSiptObjs() returns an object and does not take any parameters.In the implementation part of the code,a variable called v has been declared,which is of int type and hence,a value type.we assign 5 to v and also creates a new object up of the class BoxMe.
The next two lines are important.In the line commented BookMark1, we have called the iTakeObjs method and passed v as a parameter.recall that itakeObjs() takes in an Object as a parameter.An object is of reference type and we have passed v (a value type) as a parameter.genereally,you would be inclined to think that this would generate an error.however,it does not!!.The value type v gets implcitly converted into a reference type.This process of converting a value type into a reference type(either explicitly or implicitly ) is known as Boxing.

Following up from here,in the next line marked BookMark2 , we have created a new variable type int called unBox. We have then equated this varuiable to the iSitObjs() method.Recall that ispitObjs() does not take in any parameters but returns an object.But we have equated it to a variable of type int , which is of value type.For this reason,we have to explicitly cast the object to an int (the type conversion is done enclosing the desired datatype in paranthesis).This process of converting a reference type into a value type is known as Unboxing

However Note that in the mentioned example,Unboxing required an explicit cast.The runtime performs a check to make sure that the specified value type matches the type contained in the reference type.If the check in this fails,an exception is thrown,which,if not taken care of,will terminate the application.

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BOXING AND UNBOXING IN C#

BOXING AND UNBOXING IN C#

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