why we need to declare the collection classes polymorphically

[Maheswaran Devaraj]

Hi All,


What is the benefit of declaring the collection classes polymorphically

 

    List<String> sList = new ArrayList<String>();

   

thanks and regards,
Mahes

[Christophe Verré]

Quoting this page :
When you take an element out of a Collection, you must cast it to the type of element that is stored in the collection. Besides being inconvenient, this is unsafe. The compiler does not check that your cast is the same as the collection's type, so the cast can fail at run time.

[Moojid Hamid]

Christophe Verré wrote:Quoting this page : When you take an element out of a Collection, you must cast it to the type of element that is stored in the collection. Besides being inconvenient, this is unsafe. The compiler does not check that your cast is the same as the collection's type, so the cast can fail at run time.

As far as I understand the question is about the OO design principle "Program to interface not implementation", it is not about generics. There are many advantages, biggest one being loose coupling and flexible design. It allows for the implementation to be changed with minimal code changes.

This is one of the core OO design principles. To really appreciate the benefits, it would be a good idea to read a book on design patterns. Head first series has a good one on this topic that makes the design principles and design patterns easy to understand.