Basic Java - 2

In interviews, they might want to get your idea on re-usability concepts and how you will really re-use code from a design perspective.

What is an Abstract class ?
What is an interface ?
What are the differences ?
When you use Abstract class ? When you use interface ?
Can abstract class have constructors ?

Java is pass by value...

Try to swap the reference :)

Threads, wait, sleep, notify etc.

lock for static and non static method.