Question

当我尝试在我的银行帐户计划中创建新客户时，我收到此例外：

Exception in thread "main" java.lang.NullPointerException
    at bank.program.Customer.addAccount(Customer.java:18)
    at bank.program.BankProgram.main(BankProgram.java:24)
Java Result: 1

这是什么意思，我需要改变什么才能摆脱它？

Bank上课：

public class Bank {
    String bankName;    
    private ArrayList<Customer> customers = new ArrayList<Customer>();  

    Bank(String bankName) {
        this.bankName = bankName;
    }

    public void addCustomer(Customer newCustomer) {
        customers.add(newCustomer);
    }
}

Account上课：

public abstract class Account {
    protected double balance = 0;
    protected String accountId;

    public Account() {}  //Defaultkonstruktor

    public Account(double bal, String id) {   //Konstruktor
        if (balance >= 0) {
           balance = bal;
        }
        else {
            balance = 0;
        }
        accountId = id;
    }

    public abstract void deposit(double amount);    

    public abstract void withdraw(double amount);

    public abstract double getBalance();

    public abstract String getAccountId();

    public void transfer(double amount, Account account) {
        account.deposit(amount);
        balance -= amount;
    }
}

SavingsAccount上课：

public class SavingsAccount extends Account {
    private double interest = 2.9;

    public SavingsAccount() {     
        super();
    }

    public SavingsAccount(double bal, String id) {   
        super(bal, id);
    }

    @Override
    public void deposit(double amount) {

    }

    @Override
    public void withdraw(double amount) {

    }

    @Override  
    public double getBalance() {

    }

    @Override
    public String getAccountId() {

    }
}

Customer上课：

public class Customer {
    private String firstName;
    private String lastName;
    private String number;      
    private ArrayList<Account> accounts;

    Customer(String firstName, String lastName, String number) { 
        this.firstName = firstName;
        this.lastName = lastName;
        this.number = number;
    }

    public void addAccount(SavingsAccount account) {
        accounts.add(account);
    }

    public ArrayList<Account> getAccounts() {
        return accounts;
    }
}

银行计划类：

public class BankProgram {
    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);
        int numberOfCustomers = 0;
        Bank bank = new Bank("Bank name");

        System.out.print("Enter amount to deposit: ");
        double amount = input.nextDouble();
        System.out.println("Account number: " + numberOfCustomers);
        System.out.print("First name: ");
        String firstName = input.next();
        System.out.print("Last name: ");
        String lastName = input.next();
        System.out.print("Customer number: ");
        String pnumber = input.next();

        Customer newCustomer = new Customer(firstName, lastName, pnumber);        
        SavingsAccount savingsAccount = new SavingsAccount(amount, "11");
        newCustomer.addAccount(savingsAccount);
        bank.addCustomer(newCustomer);           
    }    
}

Answer 1

您尝试在不初始化存储它们的ArrayList的情况下添加帐户。将其添加到Customer构造函数中。

this.accounts = new ArrayList<Account>();

Answer 2

在您的Customer类中，您声明ArrayList accounts。然后，您有一个名为addAccount的方法，但好像从未初始化此accounts。

在您创建Customer对象的地方，您需要说：

newCustomer.accounts = new ArrayList<Account>();

使用Java中的银行帐户的NullPointerException

2 个答案: