Question

我正在玩JAVA，想要模拟一个ATM系统。我有一个BankMember类（int accountNumber，int pin，int balance，String name）和一个使用HashMap的UserDatabase 密钥将是accountNumber，我想将BankMember存储在HashMap中。

我有一个UserInterface接受帐号和PIN码，并尝试登录UserDatabase。

我能够毫无问题地将OBJ存储到HashMap中，但是当我尝试从BankMember中调用方法时，我得到nullPointerExceptions。

Exception in thread "main" java.lang.NullPointerException
    at atm.UserDatabase.validateLogin(UserDatabase.java:65)
    at atm.TheBank.login(TheBank.java:46)
    at atm.UserInterface.validateLogin(UserInterface.java:38)
    at atm.UserInterface.login(UserInterface.java:31)
    at atm.ATM.main(ATM.java:24)
Java Result: 1

我知道我的BankMember没有正确运行方法调用，但我不知道如何解决这个问题。我不应该为此使用HashMap吗？

这是我的userDatabase类

package atm;
import java.util.HashMap;
/**
 *
 * @author Hybrid
 */
public class UserDatabase {
    BankMember bankMember;
    private int currentAccount; //when a user logs in, the currentAccount is stored for quick access to the EU's key
    private HashMap<Integer, BankMember> accountNumberAndMember; //account number, BankMember

    public UserDatabase() {
        bankMember = new BankMember();
        currentAccount = 0;
        accountNumberAndMember = new HashMap<Integer, BankMember>();
    }

    public boolean validateAccountNumberAvailable(int accountNumber) {
        boolean validate = true;
        if (accountNumberAndMember.containsKey(accountNumber)) {
            System.out.println("Account # already in use: "+ accountNumber);
            validate = false;
        }
        return validate;
    }

    private boolean validateAccountExists(int accountNumber) {
        boolean validate = true;
        if (accountNumberAndMember.containsKey(accountNumber)) {
            validate = true;
        }
        return validate;
    }

    /**
     * 
     * @param accountNumber validate the account number is not already in the database.
     * @param bankMember if the account number is not already used, then the bankMember is stored within the database
     * @return  true is bankMember stored, false if not
     */
    public boolean setUpNewUser(int accountNumber, int pin, int balance, String name) {
        boolean validate = true;
        if(!accountNumberAndMember.containsKey(accountNumber)) {
            bankMember = new BankMember(accountNumber, pin, balance, name);
            System.out.println("Member stored in database with key: " + accountNumber);
            accountNumberAndMember.put(accountNumber, bankMember);
            System.out.println(accountNumberAndMember.get(accountNumber).getName()+ " was stored in the map as a new user.");
        } else {
            System.out.println("This account has already been created\nAccount Number:"+accountNumber);
            validate = false;
        }
        return validate;
    }

    /**
     * 
     * @param accountNumber this is the key for accountNumberAndMember map
     * @param pin this is tested within the BankMember to verify it is truly them attempting to login.
     * @return true is login is successful. False if not with proper error message.
     */
    public boolean validateLogin(int accountNumber, int pin) {
        System.out.println("::::::::::::LOGIN SYSTEM::::::::::::");
        boolean validate = validateAccountExists(accountNumber);
        if(validate) {
            System.out.println("\n\n" + accountNumberAndMember.get(accountNumber).getName()); // THIS FAILS
            if(accountNumber == accountNumberAndMember.get(accountNumber).getAccountNumber()) { //if account number is within the map
                if(pin == (accountNumberAndMember.get(accountNumber).getPin())) {
                    System.out.println("Login successful");
                    currentAccount = accountNumberAndMember.get(accountNumber).getAccountNumber();
                } else {
                    System.out.println("Invalid Pin: " + pin);
                    validate = false;
                }
            } else {
                System.out.println("Invalid Account Number: "+ accountNumber);
                validate = false;
            }
        } else {
            System.out.println("The account number does not exist: " + accountNumber);
        }
        return validate;
    }

    //Resetting Map key
    public void logOff() {
        currentAccount = 0;
    }
}

Answer 1

无论如何，您的validateAccountExists方法始终会返回true。简单地

会更好

return accountNumberAndMember.containsKey(accountNumber);

为地图中存储的OBJ调用方法

1 个答案: