I don't know if this is answered in Kishori's books: I work on a Struts web application with lots of legacy code. Do you have examples of how the power of lambda expressions can help improve code in existing projects without spending an awful lot of time on refactoring?
Also, which of your books is best for experienced Java programmers who want to learn what's new in Java 8?
As far as refactoring legacy code to use lambda expressions, I think there are certainly opportunities to leverage the expressiveness and elegance that lambda expressions can bring but unless things are absolutely horrible in your legacy code, I would be inclined to leave well enough alone.
Practice only makes habit, only perfect practice makes perfect.
Practice mindfully by doing the right things and doing things right.— Junilu