Basic Java:
- what is / structure of: SDK, JVM, Java binary code, Java packages
- interface and its implementations
- (reviewers favorite) difference between interface and abstract class
- Inheritance and polymorphism
- bucle
- variable scope
- differences between primitives and objects in Java, list of primitives you remember
- recursive algorithms (usually Fibonacci sequence generator)
- basic algorithms (prime number generator, any)

Basic Java for Web:
- servlets
- http, headers, content types, etc.
- JSP (don't mention scriplets, companies hate em, say you use JSTL)
- request and response objects
- web forms
- JavaScript basics (at least you should know basic browser events)
- XHTML basics
- CSS basics

Hope this helps.
In more advanced interviews its about software architecture and related frameworks but I doubt they'd mention that considering the case.