Java interview your java should be much strong then J2EE. core java and Advance java is the basic foundation for Interview. Some of the topic about which you should know before going for a java interview are mentioned below:
1-JRE, JDK & JVM
2-OOPS
3-Different scenarios related to oops like scenarios based on compile-time and runtime polymorphism, different type of inheritence
4-exception hierarchy, checked and unchecked exception, Different scenarios related to exceptions
5-Threads , their states and ways of creating threads.
6-Collection framework and difference between different collections.
7-Generics.
8-Hashcode and equals and their contract.
9-Difference between:
String & StringBuffer
equals and ==
checked and unchecked exceptions
interface and abstract class
Thread class and runnable interface.