I agree with Colin, you do not need to know any other language to learn Java. Please do not listen to the people who say you "need to know C," or "need to have a C reference book."
Java is not based on C, C++, or C#. They have similar characteristics, but Java is not "based" on any C language.
If you know C, or any other language, it will help you with learning a new language, because this assumes that you understand the basics of programming.
Additionally, if you are familiar with object oriented languages and programming, then you should have an easy transition into Java.
In order to learn Java, just get a good introduction to Java book. Try looking at Amazon to see which ones people have said are helpful.