what is advantges of using interface reference instead of class refernce

am 2009

Hi I have one query as Consider i have ICheck interface which is implemented by class "Data". So I can access functions in Class Data using Code as 1) Data obj; obj.Fun(); 2) ICheck ck = new Data(); ck.Fun() So what is advantages of using second code.

DaveyM69

You can implement the ICheck interface in any class/struct you like. You can then use the same method an any instances of any of those classes.

Dave
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OriginalGriff

You can only derive a class from a single other class. For example

public partial class frmMain : Form
    {
    ...
    }

But you can inherit as many Interfaces as you need. For example

public partial class frmMain : Form, ICloneable, IComparable, IDisposable
    {
    ...
    }

(Not that I am suggesting that is a sensible Interface list for a form, it's just an example)

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Pete OHanlon

In your example, there's very little advantage. Where the use of the interface comes into its own is when you want to perform a specific method, e.g. Dispose an object. Rather than having to use reflection to determine whether or not an object contains that method, you can use the interface to do the action. Consider the following snippet:

Data obj = new Data();
ICheck check = obj as ICheck;
if (check != null)
check.Fun();

Now, if Data doesn't implement this interface, the code still compiles and behaves as you'd expect. This really comes into its own if you are using something like Inversion of Control where you'd use the interface to retrieve the object, e.g.:

ICheck obj = MyIocContainer.Resolve(/* some reference to the Data class);
obj.Fun();

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modified on Saturday, September 11, 2010 8:14 AM

PIEBALDconsult

Very little with a local variable -- very much with a parameter or property.

Pete OHanlon

An important one - the using () pattern wouldn't work without the use of IDisposable.

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Paul Michalik · modified on Saturday, September 11, 2010 8:14 AM

Pete O'Hanlon wrote:

Now, if Data doesn't implement this interface, the code still compiles and behaves as you'd expect.

Oh my god, no! If Data does not implement ICheck the code would not compile, at least in the statically typed polymorphic world!

Paul Michalik

Go and google for Dependency inversion. Basically, you use interfaces to loosen dependencies between components. Consider:

public class Data : IData {
private IDataChecker mDataChecker;

//...

public Data(IDataChecker pDataChecker) {
mDataChecker = pDataChecker;
}

//...
}

Your concrete Data depends only on IDataChecker interface, not on its implementation. The consequence is that you can use many different implementations of IDataChecker without changing Data.

Pete OHanlon

I checked the code I typed in and realised I'd forgotten to put as ICheck on the relevant line. I've amended it, and the code works exactly as I described. Thanks for bringing this to my attention.

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