There are many online sources for information about Java. Oracle’s official website for Java topics is http://java.sun.com; look here for the software, updates, and Java releases. This is where you’ll find the JDK, which includes the compiler, the interpreter, and other tools.
You should also visit O’Reilly’s Java site at http://oreilly.com/java. There you’ll find information about other O’Reilly Java books, and a pointer to the home page for Learning Java, http://oreil.ly/Java_4E, where you’ll find the source code examples for this book.