关于#List#的问题，如何解决？

Question

加上了这个数组赋值就报错

        UserList[0].setName("Anker");
        UserList[0].setNumber("12345");
        UserList[0].setCharacter("designer");
        UserList[0].setCode("12345");
        UserList[0].setStatus("enploy");

        UserList[1].setName("Bob");
        UserList[1].setNumber("12346");
        UserList[1].setCharacter("structer");
        UserList[1].setCode("12346");
        UserList[1].setStatus("employ");

去掉这些赋值就不报错

package com.runoob.test;

import javax.servlet.ServletException;
import javax.servlet.annotation.WebServlet;
import javax.servlet.http.HttpServlet;
import javax.servlet.http.HttpServletRequest;
import javax.servlet.http.HttpServletResponse;

import Entity.User;

import java.io.IOException;
import java.util.ArrayList;

@WebServlet("/loginServlet")
public class loginServlet extends HttpServlet {

    private static final long serialVersionUID = 1L;

    protected void doPost(HttpServletRequest request, HttpServletResponse response)
            throws ServletException, IOException {
        String name = request.getParameter("name");
        String password = request.getParameter("password");
        // ArrayList<User> UserList = null;
        int num = 3;
        User[] UserList = new User[150];
        User u = new User();
        u.setName("aaa");
        u.setNumber("12345");
        u.setCharacter("bbb");
        u.setCode("12345");
        u.setStatus("n");

        UserList[0].setName("Anker");
        UserList[0].setNumber("12345");
        UserList[0].setCharacter("designer");
        UserList[0].setCode("12345");
        UserList[0].setStatus("enploy");

        UserList[1].setName("Bob");
        UserList[1].setNumber("12346");
        UserList[1].setCharacter("structer");
        UserList[1].setCode("12346");
        UserList[1].setStatus("employ");

        /*for (int i = 0; i < 1; i++) {
            if (UserList[i].getNumber().equals(name)) {
                if (UserList[i].getCode().equals(password)) {
                    System.out.println("登录成功");
                    // 设置响应内容类型
                    response.setContentType("text/html;charset=UTF-8");

                    // 要重定向的新位置
                    /*String site = new String("http://www.runoob.com");

                    response.setStatus(response.SC_MOVED_TEMPORARILY);
                    response.setHeader("Location", site);
                }
            }
        }*/
        System.out.println(u.getCharacter());
        System.out.println(UserList[0].getCharacter());
        System.out.println("name:" + name);
        System.out.println("password:" + password);
    }
}

Answer 1

数组赋值有问题，你不能直接给数组中对象赋值，因为因为当前的对像是个null，所以会报空指针异常。

        User user1 = new User();
        user1.setName("Anker");
        user1.setNumber("12345");
        user1.setCharacter("designer");
        user1.setCode("12345");
        user1.setStatus("enploy");

        UserList[0] = user1;

你可以类似这种的，先创建对应的对象，然后将数组指向对应的对象，这样就不会有问题了。