ArrayList Student Ошибка входа в систему
У меня проблема с моим кодом. Я пытаюсь создать журнал учащегося, в котором при правильном вводе пользователь получит доступ к части memberEnter(), и, если она не верна, система должна выйти.
Я пытался скомпилировать код, и он дает мне ошибку, может кто-нибудь помочь мне исправить это?
Я получаю ошибку:
не может найти символ - переменная studentidlogin
Строка, где происходит ошибка
if(mem.studentidlogin = ("\n Not a member "))
в main метод MainSystem (также отмечено в самом коде).
Основной системный код:
import java.io.*;//imports the io package
import java.util.Scanner;//imports scanner
import java.util.*;//imports the util package
public class MainSystem {
static String fileName = null;
static Library lib = new Library();
static Scanner in = new Scanner(System.in);
static Boolean running = true;
static Member mem = new Member();//static variables that can be initialised at compile time, but can be modified at run time
public static void main(String[] args) throws IOException {// there has to be an input/output
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));//allows the user to type in the script.
String user, password;
while (running) {
System.out.println("\nEnter 0 To login as a Librarian"
+ "\nEnter 1 to Login"
+ "\nEnter 2 to Sign Up");//first display screen in the interface.
int answer = in.nextInt();
switch (answer) {
case 0:
System.out.println("\nEnter Username: ");
user = br.readLine();
System.out.println("\nEnter Password: ");
password = br.readLine();//if '0' is selected this is displayed.
if (user.matches("enter") && (password.matches("Password")))// if 0 is entered this has to be entered.
{
librairanEnter();
break;
}
else
{
System.exit(0);
}
case 1:
String studentidlogin;
System.out.println("\nEnter Student ID: ");
studentidlogin = br.readLine();//if '1' is pressed this is displayed
System.out.println(mem.studentidlogin(studentidlogin));
/************* ERROR OCCURS HERE **************/
if(mem.studentidlogin = ("\n Not a member "))
{
System.exit(0);
}else
{
memberEnter();
break;
}
case 2:
newMember();//if '2' is selected this is displayed.
break;
}
}
}
private static void newMember() throws IOException
{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
int libraryNumber;
String StudentID, Username, FullName, Address, email, PhoneNumber;
System.out.println("\nEnter Library Number: ");
libraryNumber= Integer.parseInt(br.readLine());;//prompts user to enter library number.
System.out.println("\nEnter Student ID: ");//prompts user to enter student id.
StudentID = br.readLine();
System.out.println("\nEnter Full Name: ");//prompts user to enter full name
FullName = br.readLine();
System.out.println("\nEnter Username: ");//prompts user to enter username
Username = br.readLine();
System.out.println("\nEnter E-Mail Address: ");//prompts user to enter an email address
email = br.readLine();
System.out.println("\nEnter Home Address: ");//prompts user to enter home address
Address = br.readLine();
System.out.println("\nEnter Phone Number: ");//prompts user to enter phone number
PhoneNumber = br.readLine();
StudentSignUp b = new StudentSignUp(libraryNumber, FullName, StudentID, Username, Address, email, PhoneNumber);
mem.newMember(b);
System.out.println("\nThankyou. You can now Login.: ");// prompts user that they can now sign in.
}
private static void memberEnter() throws IOException {
while (running) {
System.out.println("\nEnter 0 for load a library."
+ "\nEnter 1 for save and quit"
+ "\nEnter 2 for list all books in library"
+ "\nEnter 3 for Search For A Book");//options available if member is enters.
int answer = in.nextInt();
switch (answer) {
case 0:
System.out.println("Enter the file name to load");
loadScript(in.next());//loads previously saved script
break;
case 1:
saveAndQuit();//saves and quits from the system
break;
case 2:
System.out.println(lib.toString());//lists all the books in the library
break;
case 3:
searchBook();//searches for a book
break;
}
}
System.exit(0);
}
private static void librairanEnter() throws IOException {
while (running) {
System.out.println("\nEnter 0 for load a library."
+ "\nEnter 1 for save and quit"
+ "\nEnter 2 for list all books in library"
+ "\nEnter 3 for add book to library"
+ "\nEnter 4 for Search For A Book"
+ "\nEnter 5 for list of current members"
+ "\nEnter 6 to borrow a book"
+ "\nEnter 7 to return a book");//options available if the librarian logs in.
int answer = in.nextInt();
switch (answer) {
case 0:
System.out.println("Enter the file name to load");
loadScript(in.next());//loads previously saved libraries
break;
case 1:
saveAndQuit();//saves and quits
break;
case 2:
System.out.println(lib.toString());//prints current books in library
break;
case 3:
addBook();//adds a book to the system
break;
case 4:
searchBook();//searches for a book in the system
case 5:
System.out.println(mem.toString());//list of current members
break;
case 6:
borrowBook();//allows to borrow a book.
case 7:
returnBook();//allows to return a book.
}
}
System.exit(0);//exits from the system/
}
private static void addBook() throws IOException
{
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
int isbn, numcopies;
String author, title, genre;// initializes the variables
System.out.println("\nEnter ISBN: ");
isbn = Integer.parseInt(br.readLine());//prompts user to enter isbn
System.out.println("\nEnter Author: ");//prompts user to enter the auth
author = br.readLine();
System.out.println("\nEnter Title: ");//prompts user to enter title
title = br.readLine();
System.out.println("\nEnter Genre: ");//prompts user to enter genre
genre = br.readLine();
System.out.println("\nEnter Number Of Copies: ");//prompts user to enter number of copies
numcopies = Integer.parseInt(br.readLine());
Book b = new Book(isbn, author, title, genre, numcopies);//Creates the new book and adds it to the library
lib.addBook(b);
}
private static void saveAndQuit() {//saves and quits
// TODO Auto-generated method stub
System.out.println("Enter file name: ");//prompts the user to enter the file name.
fileName = in.next() + ".ser";//saves the file name
running = false;
FileOutputStream fos = null;
ObjectOutputStream out = null;
try {
fos = new FileOutputStream(fileName);
out = new ObjectOutputStream(fos);
out.writeObject(lib);
fos.close();
out.close();
} catch (FileNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
}
private static void loadScript(String name) {//loads a previously saved script
// TODO Auto-generated method stub
FileInputStream fis = null;
ObjectInputStream in = null;
File file = new File(name + ".ser");
if (file.exists()) {
try {
fis = new FileInputStream(file);
in = new ObjectInputStream(fis);
lib = (Library) in.readObject();
fis.close();
in.close();
} catch (IOException e) {
// TODO Auto-generated catch block
e.printStackTrace();
} catch (ClassNotFoundException e) {
// TODO Auto-generated catch block
e.printStackTrace();
}
} else {
System.out.println("\nThe file does not exist!");
}
}
private static void searchBook() throws IOException//allows searching for a book
{
String titleSearch;
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
while(running) {
System.out.println("\nEnter 0 to search on title."////prompts the user to answer 0
+ "\nEnter 3 to go back");//promts the user to enter 3
int answer = in.nextInt();
switch (answer) {
case 0:
System.out.println("Enter the book Title");//promts the user to enter the title of the book
titleSearch = br.readLine();
System.out.println(lib.searchTitle( titleSearch));
break;
case 3:
librairanEnter();//takes the user back to the librarian home page.
}
}
}
private static void borrowBook() throws IOException
{
String titleBorrow;
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
while(running) {
System.out.println("\nEnter 0 to search on title."//prompts the user to answer 0
+ "\nEnter 3 to go back");//prompt the user to answer 3
int answer = in.nextInt();
switch (answer) {
case 0:
System.out.println("Enter the book Title");//promts the user ot enter the book title
titleBorrow = br.readLine();
System.out.println(lib.borrowBook( titleBorrow));
break;
case 3:
librairanEnter();//takes the user back to the librarian home page.
}
}
}
private static void returnBook() throws IOException
{
String returnedBook;
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));
while(running) {
System.out.println("\nEnter 0 to retrun a book."//promts the user to enter 0
+ "\nEnter 3 to go back");//prompts the user to enter 3
int answer = in.nextInt();
switch (answer) {
case 0:
System.out.println("Enter the book Title");//promts the user to enter the book title.
returnedBook = br.readLine();
System.out.println(lib.returnBook( returnedBook));
break;
case 3:
librairanEnter();//takes the user back to the librarian home page.
}
}
}
}
Класс участника:
import java.util.*;
import java.io.*;
/**
* Write a description of class Member here.
*
* @author (your name)
* @version (a version number or a date)
*/
public class Member
{
private List<StudentSignUp> memberList;//creates the array list
public Member()
{
memberList = new ArrayList<StudentSignUp>(); //makes the 'memberList' the array list.
}
public void newMember(StudentSignUp student)
{
memberList.add(student);//adds a student to the array list.
}
public String toString()
{
String totalmem = "\n ";
for (int i=0; i<memberList.size(); i++)
{
StudentSignUp b = memberList.get(i);
totalmem = totalmem + b.toString(); //prints out all students
}
return totalmem;
}
public String studentidlogin(String studentidlogin) {
if (studentidlogin == null) return "\n Not a member ";
for(int i = 0; i < memberList.size(); i++){
if(studentidlogin.equalsIgnoreCase(memberList.get(i).getStudentID())){
return memberList.get(i).toString();//allows user to search for a book in the system
}
}
return "\n Not a member "; //reachable only if no book found
}
}
3 ответа
Решение
Ваш код:
System.out.println(mem.studentidlogin(studentidlogin));
if(mem.studentidlogin = ("\n Not a member "))
Первое использование mem.studentidlogin, в println() Звоните, это правильно. поскольку studentidlogin это метод Member класс, он должен вызываться как метод - с круглыми скобками и аргументами, которые соответствуют его параметрам.
Второе использование неверно. Вы рассматриваете это, как будто это поле. Я думаю, возможно, вы ожидали, что это будет результат, который был возвращен из предыдущего вызова, но если это так, Java не работает таким образом.
Кроме того, я считаю, что вы пытаетесь сравнить его со строкой "\n Not a member ", Сравнение строк должно быть сделано только с equals() или же equalsIgnoreCase()!
Когда код стоит, похоже, что вы пытаетесь присвоить значение полю (которого не существует) внутри if утверждение, которое ожидает только логическое значение (сравнение будет == который, как я уже сказал, вы не должны использовать в любом случае, но вы используете назначение =).
У вас есть два варианта. Либо позвоните еще раз правильно:
System.out.println(mem.studentidlogin(studentidlogin));
if(mem.studentidlogin().equals("\n Not a member "))
Или, желательно, чтобы не выполнять всю работу дважды, определите переменную:
String loginResult = mem.studentidlogin(studentidlogin);
System.out.println(loginResult);
if( loginResult.equals("\n Not a member "))
Это:
public static void main(String[] args) throws IOException {// there has to be an input/output
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));//allows the user to type in the script.
String user, password;
while (running) {
System.out.println("\nEnter 0 To login as a Librarian"
+ "\nEnter 1 to Login"
+ "\nEnter 2 to Sign Up");//first display screen in the interface.
int answer = in.nextInt();
switch (answer) {
case 0:
System.out.println("\nEnter Username: ");
user = br.readLine();
System.out.println("\nEnter Password: ");
password = br.readLine();//if '0' is selected this is displayed.
if (user.matches("enter") && (password.matches("Password")))// if 0 is entered this has to be entered.
{
librairanEnter();
break;
}
else
{
System.exit(0);
}
case 1:
String studentidlogin;
System.out.println("\nEnter Student ID: ");
studentidlogin = br.readLine();//if '1' is pressed this is displayed
System.out.println(mem.studentidlogin(studentidlogin));
if(mem.studentidlogin = ("\n Not a member "))
{
System.exit(0);
}else
{
memberEnter();
break;
}
case 2:
newMember();//if '2' is selected this is displayed.
break;
}
}
}
чтобы вы сделали mem.studentidlogin вместо studentidlogin в операторе if:
public static void main(String[] args) throws IOException {// there has to be an input/output
BufferedReader br=new BufferedReader(new InputStreamReader(System.in));//allows the user to type in the script.
String user, password;
while (running) {
System.out.println("\nEnter 0 To login as a Librarian"
+ "\nEnter 1 to Login"
+ "\nEnter 2 to Sign Up");//first display screen in the interface.
int answer = in.nextInt();
switch (answer) {
case 0:
System.out.println("\nEnter Username: ");
user = br.readLine();
System.out.println("\nEnter Password: ");
password = br.readLine();//if '0' is selected this is displayed.
if (user.matches("enter") && (password.matches("Password")))// if 0 is entered this has to be entered.
{
librairanEnter();
break;
}
else
{
System.exit(0);
}
case 1:
String studentidlogin;
System.out.println("\nEnter Student ID: ");
studentidlogin = br.readLine();//if '1' is pressed this is displayed
System.out.println(mem.studentidlogin(studentidlogin));
if(studentidlogin.equals("\n Not a member "))
{
System.exit(0);
}else
{
memberEnter();
break;
}
case 2:
newMember();//if '2' is selected this is displayed.
break;
}
}
}
Ваша функция
public String studentidlogin(String studentidlogin)
принимает строковый аргумент, но вы вызываете его так:
mem.studentidlogin = ("\n Not a member ")
редактировать: просто чтобы расширить мои ответы. вам нужно решить еще несколько проблем. возможно, чтение по основам Java поможет.
например
if(studentidlogin = ("\n Not a member "))
Вы хотите сравнить две строки и использовать оператор присваивания (=), но в вашем случае вам нужен метод equals.
String str = "anything";
if (str.equals("anything")) {
//do something
}
Я думаю, что вы имели в виду использование оператора ==, но это сравнивает только две области памяти.