David Flanagan, Java in a Nutshell Edition 5, 5th ed., O'Reilly and Associates 2005. Part of the O'Reilly Java series, this book provides a concise desktop reference to Java and the API.
James Gosling, Bill Joy, and Guy Steele, The Java Language Specification, 3d ed., Addison-Wesley, 2005. This book, which is part of Addison-Wesley's Java Series, provides a detailed description of the Java language. An online version is available at
http://java.sun.com/docs/books/jls
Martin Fowler, UML Distilled, 3d ed., Addison-Wesley, 2003. This book, which is part of Addison-Wesley's Object Technology Series, provides a concise introduction to UML.
