Q:

benifits of a interfaces

suppose in case of class like
class  person
  {
     String name;
    public void setName()
     {
     }

      }
  class labor extends Person
      {
      }

in that case sub class can reuse the base class data member and function but in the case of interfaces
 interface person
  {

     public void setName();

  }
   class labor extends Person
      {
       }

here we have to give the implementation of a function then if we must have to give the implementation of a function than what is the benifit of a interfaces because if we have to give the definition then without interface we can write a new function in a class and do every thing?

A:

Interfaces declare what behavior and characteristics an object will have when implemented. They are explicitly abstract, which is why you still need to define actual implementations on your objects later.
A fairly classic example and description was provided in the answer to this question.

