Given the major differences in the core language, in effect changing Java into another language with the same name, you're not going to learn Java 7 from a book about 8.
If you're serious about learning both, get both books and use them side by side, each for the version of the language it's intended for.
Do keep in mind that most companies aren't going to change their toolset to include 8 for several years to come, in fact most are still using 6 and I have encountered 1.5 still last year.
1.4 seems to be going the way of the dodo.
AND that's just compiler and JRE versions being used. There are a lot of companies out there running 1.6 and 1.7 runtimes that still require all code to use 1.4 language level, allowing 1.5 language level only where needed for interacting with 3rd party libraries.
Given the massive changes in 8, that situation is going to only get worse. Many companies aren't going to allow any of the new stuff to be used at all.