java中常用的类，包，接口

类
String
Integer
Long
File
Date
Thread
(java.lang.Thread
Thread类的定义：public class Thread extends Object implements Runnable
)
===========================
包
java.lang.*;
java.io.*;
java.util.*;
java.sql.*;
java.math.*;
=======================
接口:
Comparable
Collection
Map
List
Runnable(java.lang.Runnable 该接口的定义public interface Runnable)