This is a broad question. The company should provide their requirements. In the general case the company advertizes their requirements and if you think you match up to the requirements you apply for the job.
Do you have the SCJP book by Kathy and Bert, may be go through it that could help you in the interview for a Jr. Java programmer because I guess it covers most of the basics. Try googling for Java interview questions and I think you would get a good idea of what they expect. Have you tried contacting them in an effort to know what they expect. Anyways, good luck and let us know what you were finally up against. Don't worry be happy