is-a Relation Question

[Vishnu Prakash]

Given the following code, which statements are true?

  
interface A{
   int value1 = 20;
}
 
class B implements A{
   int value1 = 10;
}

Options
a. Class B implements interface A.
b. Class B is-a A.
c. class B has-a A


Question: Whether option "b" is correct.

[Akhilesh Trivedi]

Hmm.. vishnu! I would like to know from where did you get the question? Hope you are not trying to replicate the following thread...

http://www.coderanch.com/t/249665/java-programmer-SCJP/certification/Implementing-interface-it

[Rick O'Shay]

The notion of IS-A is independent of Java. Java types that extend a class or implement an interface have an IS-A relationship with the class or interface. If you implement Duck you're a duck; if you extend Duck you're a Duck. Simple.

[Todd Farmer]

Originally posted by Rick O'Shay:
The notion of IS-A is independent of Java. Java types that extend a class or implement an interface have an IS-A relationship with the class or interface. If you implement Duck you're a duck; if you extend Duck you're a Duck. Simple.

In code, this would look like this:

  
A itemA = new B();

It doesn't matter whether A is an interface that B implements, or whether B is a subclass of A. Regardless, B does eveything that an A can, so B is an A.

Todd Farmer