Gosling J., Joy B., Steele G., Bracha G., Buckley A. The Java Language Specification, Java SE 8

This is the definitive technical reference for the Java programming language. Written by the inventors of Java, this book provides complete, accurate, and detailed coverage of the Java programming language. It fully describes all new features of Java SE 8, including lambda expressions, method references, default methods, type annotations, and repeating annotations.Every Java programmer should have this book as the official reference to the Java programming language. I often jump to this book when I want to understand some concepts better and deeply.