java代码，空字符或者空值在控制台输入，下面的程序要输入啥才会显示ERRORCODE=02？？急求大神解答！

Posted 2023-05-02

import java.util.Scanner;

class UdbException extends Exception
private static final long serialVersionUID = 1L;
public UdbException(String msg)
super(msg);


public class EexceptionTest
public static void throw1() throws UdbException
Scanner sc = new Scanner(System.in);
System.out.print("请输入帐号：");
String data1=sc.next();
if ((data1.equals("")==false)&&(data1.equals("udb")==false))
throw new UdbException("ERRORCODE=01");
else if (data1==null||data1.equals(""))
throw new UdbException("ERRORCODE=02");

public static void main(String[] args)
try
EexceptionTest.throw1();
catch (UdbException e)
e.printStackTrace();

参考技术A public void throw1() throws UdbException
Scanner sc = new Scanner(System.in);
System.out.print("请输入帐号：");
String data1=sc.next();
String str="^[A-Za-z]+$";
if ((data1.equals("")==false)&&(data1.equals("udb")==true))
throw new UdbException("ERRORCODE=01");

else if (data1 != str )
throw new UdbException("ERRORCODE=02");


把这个方法改了一下 你看看！追问

要求输入空字符或者空值的时候显示ERRORCODE=02

参考技术B else if (data1==null||data1.equals(""))
throw new UdbException("ERRORCODE=02");


什么 都不输入追问

直接按回车的结果就是一直换行，并没有结果啊

追答

else if (data1==null||data1.equals(""))
System.out.print("ERRORCODE=02");
throw new UdbException("ERRORCODE=02");

追问

还是不行。。。

追答if ((data1.equals("")==false)&&(data1.equals("udb")==false))
            System.out.print("ERRORCODE=01");
           throw new UdbException("ERRORCODE=01");
       else if (data1==null||data1.equals(""))
                System.out.print("ERRORCODE=02");
               throw new UdbException("ERRORCODE=02");
   
   else 
       System.out.print("ERRORCODE=03");
      throw new UdbException("ERRORCODE=03");
   

直接 回车 结果 是 什么

追问

没有结果。。必须输点啥才有结果。。。。

追答

解决了？

本回答被提问者采纳

Angular 服务问题类型字符串 |空值

【中文标题】Angular 服务问题类型字符串 |空值

【英文标题】：Angular Service Issue Type string | null

【发布时间】：2022-01-06 02:04:11

【问题描述】：

我的 Angular 代码有这个问题，顺便说一下，我在我的应用程序中使用了 Angular 13。 问题在于调用服务我试图从后端调用用户 api 并且一直面临这个问题。 我进行了很多搜索并尝试了一切以使其正常工作，但没有任何解决方案。 这是下面的代码： 这是用户服务：

import  HttpClient, HttpResponse  from '@angular/common/http';
import  Injectable  from '@angular/core';
import  Observable  from 'rxjs';
import  JwtHelperService  from '@auth0/angular-jwt';
import  environment  from 'src/environments/environment';
import  User  from "../module/user";

@Injectable(providedIn: 'root')
export class UserService 
  public apiUrl = environment.apiUrl;
  private jwtHelper = new JwtHelperService();

  constructor(private http: HttpClient) 

  login(user: User): Observable<HttpResponse<User>> 
    return this.http.post<User>(`$this.apiUrl/user/login`, user,  observe: 'response');
  

  register(user: User): Observable<HttpResponse<User>> 
    return this.http.post<User>(`$this.apiUrl/user/register`, user,  observe: 'response');
  

  updateUser(formData: FormData): Observable<User> 
    return this.http.post<User>(`$this.apiUrl/user/update`, formData);
  

  deleteUser(username: string): Observable<any> 
    return this.http.delete<any>(`$this.apiUrl/user/delete/$username`);
  

  addUserToCache(user: User): void 
    localStorage.setItem('user', JSON.stringify(user));
  

  getUserFromCache(): User 
    return JSON.parse(localStorage.getItem('user'));
  

  addTokenToCache(token: string): void 
    localStorage.setItem('token', token);
  

  getTokenFromCache(): string 
    return localStorage.getItem('token');
  

  logOut(): void 
    localStorage.removeItem('user');
    localStorage.removeItem('token');
  

  getTokenExpirationDate(): Date | null 
    return this.jwtHelper.getTokenExpirationDate(this.getTokenFromCache());
  

  isUserLoggedIn(): boolean 
    if (this.getTokenFromCache() && this.getUserFromCache() &&
      this.jwtHelper.decodeToken(this.getTokenFromCache()).sub &&
      !this.jwtHelper.isTokenExpired(this.getTokenFromCache())) 
      return true;
     else 
      this.logOut();
      return false;
    
  

  createUserFormData(currentUsername: string, user: User): FormData 
    const formData = new FormData();
    formData.append('currentUsername', currentUsername);
    formData.append('username', user.username);
    formData.append('email', user.email);
    formData.append('role', user.role);
    formData.append('isActive', JSON.stringify(user.active));
    formData.append('isNonLocked', JSON.stringify(user.notLocked));
    return formData;
  

这是用户数据

export class User 
  constructor(
    public id = 0,
    public userId = '',
    public username = '',
    public email = '',
    public lastLoginDate = null,
    public logInDateDisplay = null,
    public joinDate = null,
    public active = true,
    public notLocked = true,
    public role = '',
    public authorities = []) 

这是显示给我的错误：

Error: src/app/role/admin/admin.component.ts:15:22 - error TS2339: Property 'getAdmin' does not exist on type 'UserService'.

15     this.userService.getAdmin().subscribe(
                        ~~~~~~~~


Error: src/app/role/admin/admin.component.ts:16:7 - error TS7006: Parameter 'data' implicitly has an 'any' type.

16       data => 
         ~~~~


Error: src/app/role/admin/admin.component.ts:19:7 - error TS7006: Parameter 'err' implicitly has an 'any' type.

19       err => 
         ~~~


Error: src/app/service/user.service.ts:36:23 - error TS2345: Argument of type 'string | null' is not assignable to parameter of type 'string'.
  Type 'null' is not assignable to type 'string'.

36     return JSON.parse(localStorage.getItem('user'));
                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Error: src/app/service/user.service.ts:44:5 - error TS2322: Type 'string | null' is not assignable to type 'string'.
  Type 'null' is not assignable to type 'string'.

44     return localStorage.getItem('token');
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~




** Angular Live Development Server is listening on localhost:4200, open your browser on http://localhost:4200/ **


✖ Failed to compile.
✔ Browser application bundle generation complete.

5 unchanged chunks

Build at: 2021-11-29T07:19:50.781Z - Hash: 1847dd9fe6fe2628 - Time: 350ms

Error: src/app/role/admin/admin.component.ts:15:22 - error TS2339: Property 'getAdmin' does not exist on type 'UserService'.

15     this.userService.getAdmin().subscribe(
                        ~~~~~~~~


Error: src/app/role/admin/admin.component.ts:16:7 - error TS7006: Parameter 'data' implicitly has an 'any' type.

16       data => 
         ~~~~


Error: src/app/role/admin/admin.component.ts:19:7 - error TS7006: Parameter 'err' implicitly has an 'any' type.

19       err => 
         ~~~


Error: src/app/service/user.service.ts:36:23 - error TS2345: Argument of type 'string | null' is not assignable to parameter of type 'string'.
  Type 'null' is not assignable to type 'string'.

36     return JSON.parse(localStorage.getItem('user'));
                         ~~~~~~~~~~~~~~~~~~~~~~~~~~~~


Error: src/app/service/user.service.ts:44:5 - error TS2322: Type 'string | null' is not assignable to type 'string'.
  Type 'null' is not assignable to type 'string'.

44     return localStorage.getItem('token');
       ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~




✖ Failed to compile.

【问题讨论】：

您提供的代码中没有getAdmin() 函数，这也是您遇到的第一个错误。

【参考方案1】：

尝试使用 any 而不是 User 作为参考，这样可以帮助您获取对象

getUserFromCache(): any return JSON.parse(localStorage.getItem('user'));

请先在 UserService 类中编写 getAdmin() 函数以解决此问题

【参考方案2】：

没错，当你从localStorage中取元素时返回的类型是null或者string，

getItem(key: string): string | null;

你不能解析空值，在JSON.parse之前你必须确保项目存在并且你得到它

【参考方案3】：

试试这个

return localStorage.getItem('token') || '';

这只会解决 tsc 编译器问题。

【讨论】：

最好解释一下为什么确实需要这样做。

【参考方案4】：

服务中没有调用函数

getAdmin()

在调用之前在服务中实现该功能。