Java Tutorial - http://java.sun.com/docs/books/tutorial/index.html

Java API - http://java.sun.com/j2se/1.5.0/docs/api/

Packages and classes you might want to explore:

java.io

OutputStream, InputStream

Writer, Reader - has more functionality than Streams.

PrintWriter - can print int, long, String, and much more.

BufferedReader - can read in whole lines

java.lang

System - out, in, err (similar to cout, cin, and cerr)

String

Throwable

Exceptions - getMessage and getStackTrace are helpful with debugging

java.util

Iterator

List

Map - also called a "table" ADT

ArrayList - ooh, growable arrays

LinkedList - yes, Java has built-in ADTs

Stack

Queue

TreeMap - look, a red-black tree implemented for you!

Eclipse - http://www.eclipse.org