ava.lang： 这个是系统的基础类，比如String、Math、Integer、System和Thread， 提供常用功能。java.io: 这里面是所有输入输出有关的类，比如文件操作等java.net: 这里面是与网络有关的类，比如URL,URLConnection等。java.util : 这个是系统辅助类，特别是集合类Collection,List,Map等。java.sql: 这个是数据库操作的类，Connection, Statememt，ResultSet等
Get和Post的区别
1.get是从服务器上获取数据，post是向服务器传送数据，2.get传送的数据量较小，不能大于2KB。post传送的数据量较大，一般被默认为不受限制。3.get安全性非常低，post安全性较高。但是执行效率却比Post方法好。4.在进行文件上传时只能使用post而不能是get。
Java多态的具体体现
面向对象编程有四个特征：抽象，封装，继承，多态。多态有四种体现形式：
https://www.linkedin.com/help/linkedin/answers/丽江高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/桂林高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/洛阳高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/保定高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/义乌高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/三亚高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/台州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/珠海高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/惠州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/嘉兴高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/绍兴高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/金华高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/厦门高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/大连高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/扬州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/徐州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/南通高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/常州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/泉州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/温州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/佛山高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/无锡高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/深圳高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/乌鲁木齐高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/呼和浩特高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/西宁高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/西安高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/贵阳高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/海口高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/长沙高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/郑州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/南昌高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/合肥高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/南京高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/长春高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/太原高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/银川高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/南宁高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/兰州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/昆明高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/成都高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/武汉高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/广州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/济南高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/福州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/杭州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/哈尔滨高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/沈阳高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/石家庄高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/重庆高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/上海高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/天津高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/北京高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/宁波高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/青岛高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/东莞高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/苏州高端外围【vx：9.2.3.6.8.1.8】
https://www.linkedin.com/help/linkedin/answers/丽江高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/桂林高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/洛阳高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/保定高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/义乌高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/三亚高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/台州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/珠海高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/惠州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/嘉兴高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/绍兴高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/金华高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/厦门高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/大连高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/扬州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/徐州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/南通高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/常州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/泉州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/温州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/佛山高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/无锡高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/深圳高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/乌鲁木齐高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/呼和浩特高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/西宁高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/西安高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/贵阳高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/海口高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/长沙高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/郑州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/南昌高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/合肥高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/南京高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/长春高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/太原高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/银川高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/南宁高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/兰州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/昆明高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/成都高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/武汉高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/广州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/济南高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/福州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/杭州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/哈尔滨高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/沈阳高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/石家庄高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/重庆高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/上海高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/天津高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/北京高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/宁波高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/青岛高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/东莞高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/苏州高端外围【vx：8.1.3.4.3.6.2.8】
https://www.linkedin.com/help/linkedin/answers/丽江高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/桂林高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/洛阳高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/保定高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/义乌高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/三亚高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/台州高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/珠海高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/惠州高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/嘉兴高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/绍兴高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/金华高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/厦门高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/大连高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/扬州高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/徐州高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/南通高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/常州高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/泉州高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/温州高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/佛山高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/无锡高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/深圳高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/乌鲁木齐高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/呼和浩特高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/西宁高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/西安高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/贵阳高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/海口高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/长沙高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/郑州高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/南昌高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/合肥高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/南京高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/长春高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/太原高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/银川高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/南宁高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/兰州高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/昆明高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/成都高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/武汉高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/广州高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/济南高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/福州高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/杭州高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/哈尔滨高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/沈阳高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/石家庄高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/重庆高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/上海高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/天津高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/北京高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/宁波高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/青岛高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/东莞高端外围【vx：5.2.2.0.5.2.6.4】
https://www.linkedin.com/help/linkedin/answers/苏州高端外围【vx：5.2.2.0.5.2.6.4】