Expert in 10 days... Seriously?!
Paul Boby depends on the area in which you wanna become an expert, there are a lot of different technologies based on Java, most experts are only experts in some of them.
It depends on you that I which way you will learn it , but as you already told that you know to code c language then may be it will easy for you to learn Java as java is somewhat similar to c.
Try to learn it regularly , I am sure that within 10 days you will become expert in it👍 good luck!