I don’t know how much experience you have in C ++, but provided that you have a good understanding of this language, as well as object-oriented concepts, I recommend reading Head First Java - this is a very simple reading and will introduce you to an overview of the language (including main streams and sockets).
For information on building data structures or implementing algorithms using the Java language, I recommend Data Structures and Algorithms in Java . The presentation of the books is in order - some codes crunch on some pages, but the material is solid.
Finally, the Java API is a great resource in my opinion. I can’t think about the time when I didn’t find what I was looking for on this site. Personally, I believe that if you read Head First, and then work on some personal projects and keep the Java API on your side, you will be fine.