It’s hard to Predict Java’s learning curve, but Java programming is sure to be easier for someone who has experience with either C or C++. But that comes as no wonder because Java is supposed to replace these two languages. If you’re serious about learning Java then you should read the tutorials given on either the Sun website or those written by Kevin Yank. However absolute beginners may feel that it is relatively hard to master the basics of Java, but that feeling will pass once you spend a month or so on the subject.
However if you really want to go all the way then you should certainly consider Sun certifications such as SCJA (Sun Certified Java Associate) or SCJP (Sun Certified Java Programmer). Do note that the exams are really reallty tough to pass; in fact Sun may be making quite a lot of money just because so many people fail these exams every day. However learning basic Java is just the tip of the ocean, there are so many java related technologies out there that you could probably go on learning forever.
However do be warned that Java needs a strong foundation of Object Oriented Programming. You should give OO a good hiding before you consider moving forward with Java.
But do note that all said and done Java is not a fully Object Oriented Language. This is because Java still uses primitives for variables. If you’re interested in a 100% Object Oriented language then you should study Scala, a relatively new Programming language that is almost 100% pure OO.