Java的继承体系中,因为有重写的概念,所以说this在子父类之间的调用到底是谁的方法,或者成员属性,的问题是一个值得思考的问题;
先说结论:如果在测试类中调用的是子父类同名的成员属性,这个this.成员 属性的值就是父类中这个成员属性的值,因为在Java中没有重写成员属性这一概念
,如果调用的是同名的成员方法的话,那就应该调用的是重写后的成员方法.....如果子类中没有这个成员方法,则向父类中寻找.
上代码支持论证:
package Test_This; public class Demo { public static void main(String[] args) { Fu f = new Zi(); System.out.println(f.num);//这里定义的是父类,而成员变量没有多态,所以即使你new的子类,依然指向父类的成员变量。 System.out.println(f.fun1());//不解释了,就是多态。 f.show(); } } class Fu { public String num = "父类成员变量"; public void show() { System.out.println(this.num);//因为成员变量没有多态,所以this指向当前类对象的成员变量。 System.out.println(this.fun1());//因为方法有多态,所以this指向new对象的方法。 } public String fun1() { System.out.println(this.num);//因为成员变量没有多态,所以this指向当前类对象的成员变量。 return "父类调用"; } } class Zi extends Fu { public String num = "子类成员变量"; public String fun1() { System.out.println(this.num);//因为成员变量没有多态,所以this指向当前类对象的成员变量。 return "子类调用"; } }
运行结果:
以上代码实验结果即可证明其论证;
在web开发中可以用这一特性,结合反射来抽取servlet方法
上代码:这个是父类
import java.io.IOException; import java.lang.reflect.Method; import javax.servlet.ServletException; import javax.servlet.http.HttpServlet; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; public class BaseServlet extends HttpServlet { @Override public void doGet(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { this.doPost(req, resp); } @Override public void doPost(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { // localhost:8080/Test/productServlet?method=addProduct String method = req.getParameter("method"); if (null == method || "".equals(method) || method.trim().equals("")) { method = "execute"; } // 注意:此处的this代表的是子类的对象 System.out.println("baseservlet this"); System.out.println(this); // 子类对象字节码对象 Class clazz = this.getClass(); try { // 查找子类对象对应的字节码中的名称为method的方法.这个方法的参数类型是:HttpServletRequest.class,HttpServletResponse.class Method md = clazz.getMethod(method, HttpServletRequest.class, HttpServletResponse.class); if (null != md) { String jspPath = (String) md.invoke(this, req, resp); if (null != jspPath) { req.getRequestDispatcher(jspPath).forward(req, resp); } } } catch (Exception e) { e.printStackTrace(); } } // 默认方法 public String execute(HttpServletRequest req, HttpServletResponse resp) throws ServletException, IOException { return null; } }
子类:
import java.io.IOException; import javax.servlet.ServletException; import javax.servlet.http.HttpServletRequest; import javax.servlet.http.HttpServletResponse; import cn.itcast.domain.User; import cn.itcast.service.IUserService; import cn.itcast.service.serviceImp.UserServiceImp; import cn.itcast.utils.MyBeanUtils; import cn.itcast.utils.UUIDUtils; import cn.itcast.web.base.BaseServlet; public class UserServlet extends BaseServlet { private static final long serialVersionUID = 1L; public String registUI(HttpServletRequest request, HttpServletResponse response) throws ServletException, IOException { return "/jsp/register.jsp"; } //regist public String regist(HttpServletRequest request, HttpServletResponse response) throws Exception { //接受用户的表单数据,将其封装到一个对象User上 User user=MyBeanUtils.populate(User.class, request.getParameterMap()); user.setUid(UUIDUtils.getId()); user.setCode(UUIDUtils.getUUID64()); System.out.println(user); //调用sevice用户注册功能 IUserService userService=new UserServiceImp(); userService.regist(user); //转发到个提示页面info.jsp request.setAttribute("msg", "用户注册成功,请激活"); return "/jsp/info.jsp"; } //active public String active(HttpServletRequest request, HttpServletResponse response) throws Exception { //获取用户的激活码 String code = request.getParameter("code"); //调用SERVICE层激活功能,返回用户对象 IUserService userService=new UserServiceImp(); User user=userService.active(code); System.out.println(user); if(null!=user) { //如果用户不为空,可以激活,更改用户的状态,清空用户的激活码,向request放入提示消息,转发到登录页面 user.setState(1); user.setCode(""); userService.updateUser(user); request.setAttribute("msg", "用户激活成功,请登录"); return "/jsp/login.jsp"; }else { //如果用户为空,可以失败,向request放入提示消息,转发到info.jsp页面 request.setAttribute("msg", "用户激活失败,请重新激活"); return "/jsp/info.jsp"; } } //loginUI public String loginUI(HttpServletRequest request, HttpServletResponse response) throws Exception { return "/jsp/login.jsp"; } //用户登录 //login public String login(HttpServletRequest request, HttpServletResponse response) throws Exception { //接受表单参数 User user=MyBeanUtils.populate(User.class, request.getParameterMap()); //调用业务层登录功能,返回用户对象 IUserService userService=new UserServiceImp(); User uu=userService.login(user); if(null!=uu) { //用户名不为空,登录成功,将登录成功的用户放入session,重定向到项目首页 request.getSession().setAttribute("user", uu); response.sendRedirect("/store_v4/index.jsp"); return null; }else { //用户名为空,登录失败,向request中放入提示消息,转发/jsp/info.jsp request.setAttribute("msg", "用户登录失败,请重新登录"); return "/jsp/info.jsp"; } } //logOut public String logOut(HttpServletRequest request, HttpServletResponse response) throws Exception { request.getSession().invalidate(); response.sendRedirect("/store_v4/index.jsp"); return null; } }
当请求到servlet后,在servlet
原文地址:https://www.cnblogs.com/YangGC/p/9026170.html
时间: 2024-10-09 01:33:24