A book (or web documentation structured like a book) is still my preferred way of learning most languages.
If you just dive into a language and find stuff out for yourself, you're likely to miss out on important aspects, which a good book would have delivered to you at the right time.
For example, some colleagues of mine learned Java by diving in without a book. They'd been programming in Java for some years, when I discovered they were routinely manipulating arrays of byte[] by converting the array into a String, using .substring(), then converting the String back into an array. System.ArrayCopy() is introduced on page 155 of Java In A Nutshell
I hope you recognise that learning is easier with a teacher, than alone. A good book is a cheap substitute for a good teacher. It will introduce concepts in a carefully planned order, so you can build up a thorough understanding -- not merely enough to get by.