There have been a lot of changes to Java since 1.6. The good news is there are a lot of interesting topics to learn. There are a lot of good books and web sites out there that addresses these changes. The advantage of a book is that it provides a more comprehensive coverage of many features.
As far as topics are concerned, I would look at the language changes such as the try-with-resources block in 1.7 and lambda expressions/streams in Java 1.8. There were a number of useful IO enhancements made to 1.7 that can be quite useful if you applications have a need for that. In Java 1.8, improvements in date and time are significant.