Best/quickest way to learn Java for a seasoned .NET/C# and C++ developer
I suggest starting with The Java Language Specification. I don't think there is any quicker or more comprehensive way of gaining an understanding of the language for a seasoned programmer.
Followed by Java Collections Tutorial.
Followed by
java.lang.*andjava.util.*classes, interfaces and packages.
This will give a good basis for learning and understanding any other branch of Java as it becomes necessary.
I would take a completely different approach to reading books upfront. Simply download an IDE and get coding. The netbeans tutorials tend to get you up and running with a variety to technologies very quickly.
If you can code C# then you should have no problem getting something up and running.
Once you have some code up and running that is when you would then dig out the likes of effective Java.
Karl