Question

我在项目中有以下课程：

帐户
客户
名称：fName和lName（都是字符串字段）
日期：年，月，日（均为int字段）
银行：包含帐户集合
InputReader：从键盘读取输入

Account对象需要Customer对象和期初余额。 Customer对象需要Name对象和Date对象。 Name对象需要字符串来表示名字和姓氏我需要询问用户详细信息以创建名称和日期对象，以及期初余额。

我必须通过从用户那里获取相关信息来创建一个新帐户，即它要求用户键入客户的姓名，出生日期等。它读取用户的回复，创建帐户并将其添加到银行。

当我运行public void createNewAccount（）方法时，我不断收到一条错误消息“java.lang.NullPointerException”。非常感谢任何帮助。提前致谢。

以下是我的班级类的源代码。

import java.util.ArrayList;

public class Bank
{
    public static final double INTEREST_RATE = 0.012;//1.2%
    // instance variables - replace the example below with your own
    private ArrayList<Account> accounts;
    private InputReader reader;
    private Name fullName;
    private Date dateOfBirth;

    /**
     * Constructor for objects of class Bank
     */
    public Bank()
    {
        // initialise instance variables

    }

    /*
     * Adds an existing Account to the bank
     * @param account
     */
    public void addAccount(Account account)
    {
        accounts.add(account);
    }

       public void createNewAccount() { 

        System.out.println("Please enter your first name: ");
        String firstName = reader.readString();

        System.out.println("Hello " + firstName + ". " + "What is your last name?");
        String lastName = reader.readString();
        System.out.println("Your last name is " + lastName);


        System.out.println("Please enter your year of birth: ");
        int thisYear = reader.readInt();

        System.out.println("Please enter your month of birth: ");
        int thisMonth = reader.readInt();

        System.out.println("Please enter your date of birth: ");
        int thisDay = reader.readInt();

        Name theName = new Name(firstName, lastName);
        Date theDateOfBirth = new Date(thisYear, thisMonth, thisDay);

    }


}

Answer 1

您必须先初始化阅读器，然后才能尝试阅读。

Answer 2

Scanner scanner = new Scanner(System.in);

The scanner object has a lot of functions you can use;

Answer 3

您的InputReader阅读器已声明，但未初始化，因此为NullPointerExceptin。将其更改为更常用的：

Scanner scanner = new Scanner(System.in);

然后你可以使用它的方法进行用户输入：

scanner.nextLine() for strings

scanner.nextInt() for ints

scanner.nextDouble() for doubles

等

检查文档here。

Answer 4

您可以使用扫描仪更换阅读器。这样的事情。

    Scanner scan = new Scanner(System.in);
    System.out.println("Please enter your first name: ");
    String firstName = scan.next();

    System.out.println("Hello " + firstName + ". " + "What is your last name?");
    String lastName = scan.next();
    System.out.println("Your last name is " + lastName);


    System.out.println("Please enter your year of birth: ");
    int thisYear = scan.nextInt();

    System.out.println("Please enter your month of birth: ");
    int thisMonth = scan.nextInt();

    System.out.println("Please enter your date of birth: ");
    int thisDay = scan.nextInt();

  //Then do what you are supposed to do......

Answer 5

您需要初始化实例变量：

public class Bank
{
    public static final double INTEREST_RATE = 0.012;

    private ArrayList<Account> accounts;
    private InputReader reader;
    private Name fullName;
    private Date dateOfBirth;

    public Bank()
    {
        // initialise instance variables <- where it says to
        accounts = new ArrayList<Account>();
        reader = new InputReader();
        ...
    }

InputReader必须是赋值包的一部分，所以我不知道它的构造函数是什么。

如何使用用户输入创建银行帐户？

5 个答案: