For the first 6 months of time you spend working on Java, tutorials, blogs and your fellow programmerette should be enough to let you do your job effectively. read more
But you should get the specification (maybe not physically, you can find it online: Java SE Specifications) and have it ready. As you get more experienced with Java and you encounter code or tricky questions that you don’t know the answer to, then you should start reading the JLS. read more
Yes, if you really want to know how the language and the virtual machine are really supposed to work then you should read their actual specifications. read more
The specification needs to be accurate, so all yes/no questions can be answered definitively. Thise who wrote and maintained java compilers /must/ have read it to be able to know how to implement Them. read more