A Google search for "java interview questions" will find several  
(thousands even).  You could also search for example questions for the Sun  
Certified Java Programmer exam, as these might be the kind of things you  
would be asked.

Beyond giving you practice, preparing for particular questions will only  
be helpful if you get lucky and meet the same questions.

It depends on what you claim to know and what the position requires.  For  
entry-level, at the very least, as well as knowing all the main language  
features (classes, interfaces, exceptions, synchronisation, etc.), you  
would be expected to know about and be able to use most of the classes in  
the java.lang, java.util and java.io packages.  Pay particular attention  
to the collections classes.  You should know which ones to use in which  
circumstances (e.g. what are the advantages of a LinkedList over an  
ArrayList).  Make sure you know, and can explain clearly, what the  
hashCode method is for, how it relates to the equals method and how it is  
used by collections classes (this is a typical question to separate the  
wheat from the chaf).

You are unlikely only to be asked coding questions.  You may be asked  
about general OO concepts such as polymorphism, or asked about design  
issues.  You could prepare for this by considering the design of some of  
these core classes.  Have a look at the way interfaces (particularly List,  
Set and Map) and abstract classes are used in the collections heirarchy  
and think about why these decisions were made.  If you don't know already,  
find out what the Decorator pattern is and then try to identify how it is  
used in the java.io package.

Good luck,

Dan.