为什么我的程序中始终会删除存储的值

Question

Ok, so I'm trying to finish our simple project for Data Strcutures but there is always some error that just keep showing up on my program. I have fixed some of them but there is this one that makes me want to give up. Maybe you guys could help me find the solution?

Here is my code (class LogInSystem):

    // NMQ

    import java.util.ArrayList;
    import java.util.Scanner;
    import java.util.Vector;

public class LogInSystem {
    private static final int MAX_SEATS = 10;

    Vector<String> username = new Vector<String>();
    ArrayList<String> password = new ArrayList<String>();

    int p;
    String Username, Password, rUsername, rPassword;

    private Scanner input = new Scanner(System.in);


    public LogInSystem() {
        loginScreen();
    }
    private void loginScreen() {
        boolean done = false;

        do {
            printMainMenu();
            int choice = getMainMenuChoice();

            switch (choice) {
            case 1: // Log In
                logIn();
                break;

            case 2: // To Register
                register();
                break;

            case 3: // Exit
                done = true;
                break;
            }

        } while (!done);
    }

    //Registration

    private void register() {
        System.out.println("Input a Username");
        Username = input.next();
        System.out.println("Input a Password");
        Password = input.next();
        System.out.println("... Registered!");

    }

    //Log In

    private void logIn() {
        p = 0;
        System.out.println("Input a Username");
        rUsername = input.next();
        System.out.println("Input a Password");
        rPassword = input.next();

        // If the log in is successful it will got to the next menu

        if(rUsername.equals(Username)&& rPassword.equals(Password))
        {
            System.out.println("... Logging In");
            boolean done = false;

            String[] seats = new String[MAX_SEATS]; // the item list
            initializeItems(seats);
         // Printing of 2nd menu
            do {
                printMainMenu2();
                int choice = getMainMenuChoice2(); // choice off of the main menu

                switch (choice) {
                case 1: // Adding Seat
                    addSeat(seats);
                    break;
                case 2: // Viewing Seat List
                    viewSeatList(seats);
                    break;
                case 3: // Exit
                    done = true;
                    break;
                }

            } while (!done);
        }

        else
            System.out.println("Invalid log in, please try again.");

    }
    private int getMainMenuChoice() {
        int choice; // choice entered
        boolean valid = false; // is choice valid?

        do {
            System.out.print(">>>>> ");
            choice = cineplexError.readInt();

            if (1 <= choice && choice <= 4) {
                valid = true;
            } else {
                System.out.println("Invalid choice.");
            }
        } while (!valid);

        return choice;
    }
    private void printMainMenu() {
        System.out.println("\nMain Menu\n");
        System.out.println("Press 1 to Log In");
        System.out.println("Press 2 to Register");
        System.out.println("Press 3 to Exit");
        System.out.println();
    }
    public static void main(String[] args) {
        new LogInSystem();
    }

    int getMainMenuChoice2() {
        int choice; // choice entered
        boolean valid = false; // is choice valid?

        do {
            System.out.print(">>>>> ");
            choice = cineplexError.readInt();

            if (1 <= choice && choice <= 4) {
                valid = true;
            } else {
                System.out.println("Invalid choice.");
            }
        } while (!valid);

        return choice;
    }
    void printMainMenu2() {
        System.out.println("\nMain Menu\n");
        System.out.println("Press 1 to Reserve a Seat");
        System.out.println("Press 2 to View the Seat List");
        System.out.println("Press 3 to Exit Buying");
        System.out.println();
    }
    void initializeItems(String[] seats) {
        for (int i = 0; i < seats.length; i++) {
            seats[i] = "";
        }
    }
    void addSeat(String[] seats) {
           int seatIndex = findEmptySeatList(seats); // index of first empty item list
            if (seatIndex == seats.length) {
                System.out.println("Seat is already occupied. Sorry.");
            } 

            else {
                String seat = getSeatName(); // seat's name
                seats[seatIndex] = seat;
                System.out.println(seat + " is on seat list #"
                        + (seatIndex + 1));
            }
        }
    int findEmptySeatList(String[] seat) {
        for (int i = 0; i < seat.length; i++) {
            if (isEmpty(seat, i)) {
                return i;
            }
        }

        return seat.length;
    }
    boolean isEmpty(String[] seats, int seatIndex) {
        return seats[seatIndex].equals("");
    }
    String getSeatName() {
        System.out.print("Enter the name of reservator: ");
        return cineplexError.readString();
    }
    void viewSeatList(String[] seats) {
        System.out.println("\nSeat List\n");
        for (int i = 0; i < seats.length; i++) {
            System.out.println((i + 1) + ". " + seats[i]);
        }
    }
}

Here is the other class (cineplexError):

// NMQ

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

public class cineplexError {
    private  static BufferedReader in = new BufferedReader(new InputStreamReader(System.in));
    private  static String integerReprompt = "Invalid integer. Try again: ";
    private  static String doubleReprompt = "Invalid double. Try again: ";
    private  static String charReprompt = "Invalid character. Try again: ";

    public static String readString() {
        String s = null;
        try {
            s = in.readLine();
        } catch (IOException ex) {}
        return s;
    }

    public static char readChar() {
        char c = 0;
        String s = null;
        try {
            s = in.readLine();
        } catch (IOException ex) {}
                if (s.length() == 1) {
                    c = s.charAt(0);
//                  valid = true;
                } else {
                    System.out.print(charReprompt);
                }
        return c;
    }

    public static int readInt() {
        int i = 0;

            boolean valid = false;

            try {
                    i = Integer.parseInt(in.readLine());
            } catch (IOException ex) {
                System.out.print(integerReprompt);
                }
                    valid = true;



        return i;
    }

    public static double readDouble() {
        double d = 0.0;

        boolean valid = true;

        try {
                    d = Double.parseDouble(in.readLine());
        } catch (IOException ex) {}
                    valid = true;
                    valid = false;
                    System.out.print(doubleReprompt);


        return d;
    }

    public void pause() {
            System.out.print("Press enter to continue...");
            try {
            in.readLine();
            } catch (IOException ex) {}
        }

    public static void setIntegerReprompt(String prompt) {
        integerReprompt = prompt;
    }

    public void setDoubleReprompt(String prompt) {
        doubleReprompt = prompt;
    }

    public void setCharReprompt(String prompt) {
        charReprompt = prompt;
    }

 }

---

The bug in the program is that whenever I reserve a seat and log out and log in again the name of the reservator or the name of the one that reserves a seat is being erased when I view the seat list. Should I put a control statement that makes the value stored permanently? Can you help me out? Thanks.

Answer 1

you need to make seats a member of class as password and username. it is now only defined within a function, so at the end of function call it is destroyed.

Answer 2

Line 73:   String[] seats = new String[MAX_SEATS]; // the item list
Line 74:   initializeItems(seats);

Every time you call logIn you are re-initializing the list of seats to all empty strings. That initialization should be done in the constructor. So move Line 73 (declaration of String[] seats) to be an instance variable of the class, and move Line 74 to be in the constructor.