by Allen B. Downey: Focuses on the logic of programming and is excellent for absolute beginners. You can find the PDF on GitHub .
by David J. Eck: A comprehensive open-source textbook widely used in universities. It is available for free download at Hobart and William Smith Colleges . Download Java Programming Fundamentals pdf
Most of these guides follow a structured path to help you master the language: Intro to Java Programming - Course for Absolute Beginners by Allen B