This week's book giveaway is in the OO, Patterns, UML and Refactoring forum. We're giving away four copies of Refactoring for Software Design Smells: Managing Technical Debt and have Girish Suryanarayana, Ganesh Samarthyam & Tushar Sharma on-line! See this thread for details.
Is-A requires two class types - this can be explained on the basis of 1st point Inheritance means class A extends B means Class A IS-A B
Also interfaces are like abstract classes interface A implements B ie it requires atleast two class types two show the IS-A relationship
Use of Inheritance means code reuse or use polymorphism thats why IS-A relys on polymorphism
would really appreciate some more people comment on this