Hi
I would agree with Jesper, although I would put more importance on learning Object Orientated Analaysis & Design, design
patterns and the like.
If you are serious about learning Java, get a book or web resource on Java certification, I have been coding Java for years, and have recently started to look into certification, and the book is helping me to learn the flaws and holes in my own understand of Java.
I am using "Sun Certified Programmer for Java 5: Study Guide Exam 310-055, by Kathy Sierra and Bert Bates" It is an easy read, in the vain of the "Head First..." range of books.
I also personally find the Java community more vibrant then that for C#.
(I recently coded in C#/.net for 2years, I was able to transfer my Java skills and "design" abilities to the C# world quite easierly, the main problems were where the syntax differs between the two langauges)