Nope, you can start java  from the gecko. I recommend
to log into http://sun.java.com search around for
technology blueprint or overall picture, see how C and
C++ play in the overall picture. That's about it.

The reason why people tell you to know C++ because the
concept of Object Oriented is too complicated for
them. Who knows you may be smarter-- Different folk
have different yolks.

People who know C & C++ seems to grasp Java quicker
because they can spot the similarity in syntax. This
bring me a story at my company.

I have a "kid" about 18 or 19 years old who primary
duty is office materials inventory. Who happens never
get on my nerve. He wants to do things like the
developer/programmer because to him it is very easy
job and have the honor to lunch or dinner with the
executives once awhile??? I conduct an impromptu
interview and know the kid never taking a computer
course in his life.

I lend him Arnold, Gosling, & Holmes's The Java
Programming Language, 3rd ed., Joshua Bloch's
Effective Java, and Kathy Sierra & Bert Bates's Sun
Certified Programmer & Developer. At the same time, I
check his profile from human resource department and
found the kid honest.

After two months, he shows me his Sun Certified
Programmer Exam Result 98% with category breaking
down. The myth about elite IT Engineer that Silicon
Valley painted just shatter right on front of me.

Now, the kid is Java Programmer handle entry level
task and on company paid tuition for as long as he
could handle.