常用的类：
BufferedReader ,BufferedWriter
FileReader ,FileWirter
String ,Integer
Date ,Class
HashMap ,Object
Runtime ,file
Integer ,Long
Thread
常用的包：
java.lang java.io
java.util java.sql
java.swt java.math
javax.servlet org.apache.struts.action
org.hibernate
常用的接口：
List Map
Document NodeList
Servlet HttpServletResponse
Session Transaction
HttpSession Iterator
Comparable Clone
Serializable Runnable