Code To Interfaces Doubt???

[satya mahapatra]

Hi All,

How code to inetrfaces is helping to acheive loose coupling and what is advantage of loose coupling.

Can anyone pls explain this with the help of an example.

Thanks,
Satya

[Joe San]

I guess this question would be better answered at the SCJP forum.

[satya mahapatra]

As Code To Interface is one of the j2ee design principle thats why I have put the question in this forum.

[Saurabh Kumar]

Hi,

"Code to Interface" means you write your program to an abstract type(a super class or an interface) and not to a concrete implementation.

for example:
when you write:

  ArrayList myList= new ArrayList(); 

You are coding to the concrete implementation- ArrayList.

whereas when you write:

 List myList=new ArrayList()   

you are coding to an abstract type: List interface.

So, in the first piece of code, the object "myList" is highly coupled to a particular concrete implementation(ArrayList) whereas in the second piece of code it is loosely coupled.Moreover, doing so, you can achieve better flexibility. You can use 'myList' object for any concrete implementation of the abstract type- List.

Hope this helps.

Thanks and regards,
Saurabh

[Christophe Verré]

Thank you all for answering, but I'm moving this thread which is not related to SCWCD.

[Garrett Rowe]

In my opinion both declarations are equally tightly coupled.

List one = new ArrayList();
ArrayList two = new ArrayList();

Neither line will compile if ArrayList class is not present on the classpath at compile time. Any time you mention a concrete type in your code you are tightly coupled to that implementation. However you don't have to couple clients that use your code to that type. A method that returns an ArrayList reveals implementation details, a method that takes an ArrayList as a parameter forces client code into a particular implementation. Not so if List or Collection is used as the parameter or return type of the method.

[Stan James]

Right, those examples don't quite get to the value of interfaces or abstraction. Let's look at a method:

public void doSomething( List list )
{
   if( list.size() > 0 )
      do something very cool
}

Because this uses List I can pass it any kind of List ... Arraylist, LinkedList or other List implementations nobody has even thought of yet. If the method had been written:

public void doSomething( ArrayList list ) ...

you couldn't call it with those other things.

That just barely scratches the surface of the goodness of abstractions and interfaces. Does it seem worth while so far?

[Saurabh Kumar]

Thats true...
I had the same thing in mind but perhaps couldnot explain in better way as you guys did.

Thanks for your explanations.

Thanks and regards,
Saurabh

[satya mahapatra]

Thanks a lot guys. You all have explained the concept so nicely.