Interview experience

Recently, we interviewed a candidate for Senior Java Developer position.

I was surprised to find that person couldn't even answer few fundamental questions like:

1. How do HashMap works? Why do we have to implement hashcode and equals method of an object?

2. Parallel garabage collector in Java 1.4 onwards.

3. Pros and cons of adding index to a database column

At a Senior Developer position, I expect people to answer these basic questions.