JAVA...
On
to Java 
On to Java: Fast Travel on
the Natural Path to Java Essentials and Effective
Programming Practices is a clear, concise, no-nonsense
book on Java that would appeal most to serious programmers.
Authored by an MIT CS prof and a real-world Java expert.
Written in a terse, slide-show style that presents
each essential idea in a brief paragraph without unnecessary
verbiage.
Karel
J. Robot 
Karel J. Robot: A Gentle Introduction
to the Art of Object-Oriented Programming in Java
is available online free of charge.
Java
Precisely 
Free online
book Java Precisely provides a concise reference for
the Java programming language and some of its essential
libraries. The book covers Java 2, versions 1.3 and
1.4. It is intended both for students learning Java
and for more experienced Java programmers.
Interactive
Programming In Java
Free online book Interactive
Programming In Java by Lynn Andrea Stein is divided
into following parts: Part 1: Introduction to Interactive
Program Design, Part 2: Entities and Interactions,
Part 3: Refining Designs, Part 4: Refining Interactions
and Part 5: Systems of Objects.
Java
Data Structures (2nd edition)
Java Data Structures by theparticle.com
is a free online Java book
Java
