Question

我试图在一个对象数组中输入值，但我似乎无法让它工作。从本质上讲，我只需要创建一系列可以提取和存款的帐户。我试着去找我的教授寻求帮助，她说我只需要初始化值，因为它们最初都是null。但是，我不确定这个的语法，我的书有类似的方法，但不完全一样。有人可以帮我这个吗？

import java.util.Scanner;
import java.text.NumberFormat;
public class AccountMain
{
  public static void main(String[] args)
  {
    Scanner scan = new Scanner(System.in);
    Account[] acct = new Account[30];
    for (int count = 0; count < 30; count++)
    {
      acct[count] = new Account("", 0, 0);
    }
                                                                                //creates accounts
    acct[0].Account("Jerry Longhorn", 1, 50.50);
    acct[1].Account("Jimmy Longhorn", 2, 700.20);
    acct[2].Account("Jenny Longhorn", 3, 10000.50);
    acct[3].Account("Jeffrey Longhorn", 4, 400.20);
    acct[4].Account("Jack Longhorn", 5, 500.20);

                                                                                //Determines withdraw or deposit
    System.out.println("Please enter your account number: ");
    int num = scan.nextInt();
    System.out.println("Enter W for withdrawl; D for deposit: ");
    char choice = scan.next().charAt(0);

    if (choice == 'W' || choice == 'w' || choice == 'D' || choice == 'd')
    {

      if (choice == 'W' || choice == 'w')
      {
        System.out.println("Enter amount to withdraw: ");
        double WithdrawMoney = scan.nextDouble();
        acct[--num].withdraw(WithdrawMoney);                                    //MUST --num in order to account for 0
        System.out.println("User # " + num + " funds after withdraw: " + acct[--num].getBalance() + "$");
        System.out.println("User # " + num + " funds after interest: " + acct[--num].addInterest() + "$");
      }
      if (choice == 'D' || choice == 'd')
      {
        System.out.println("Enter amount to deposit: ");
        double DepositMoney = scan.nextDouble();
        acct[--num].deposite(DepositMoney);                                    //MUST --num in order to account for 0
        System.out.println("User # " + num + " funds after deposit: " + acct[--num].getBalance() + "$");
        System.out.println("User # " + num + " funds after interest: " + acct[--num].addInterest() + "$");
      }
      else
        System.out.println("Invalid input.");



    }
  }
}

支持班：

import java.text.NumberFormat; //links to Part2

public class Account
{
  private final double RATE = 0.03; //Interest is 3%

  private int acctNumber;
  private String name;
  private double balance;

  //Defines owner, account number, and initial balance.
  public Account(String owner, int account, double initial)
  {
    name = owner;
    acctNumber = account;
    balance = initial;
  }

  //deposits a specified amount and returns new balance
  public double deposit(double amount)
  {
    balance = balance + amount;
    return balance;
  }

  //withdraws the specified amount from the account and applies the fee
  //                                                  + returns balance
  public double withdraw(double amount)
  {
    int fee = 1;
    balance = balance - amount - fee;
    return balance;
  }

  //Adds interest to the account
  public double addInterest()
  {
    balance += (balance * RATE);
    return balance;
  }
  public double getBalance()
  {
    return balance;
  }

  //returns a one line description of the account as a string
  public String toString()
  {
    NumberFormat fmt = NumberFormat.getCurrencyInstance();
    return acctNumber + "/t" + name + "/t" + fmt.format(balance);
  }
}

Answer 1

这是无效的语法：

acct[0].Account("Jerry Longhorn", 1, 50.50);
acct[1].Account("Jimmy Longhorn", 2, 700.20);
acct[2].Account("Jenny Longhorn", 3, 10000.50);
acct[3].Account("Jeffrey Longhorn", 4, 400.20);
acct[4].Account("Jack Longhorn", 5, 500.20);

你的意思可能是：

acct[0] = new Account("Jerry Longhorn", 1, 50.50);
acct[1] = new Account("Jimmy Longhorn", 2, 700.20);
acct[2] = new Account("Jenny Longhorn", 3, 10000.50);
acct[3] = new Account("Jeffrey Longhorn", 4, 400.20);
acct[4] = new Account("Jack Longhorn", 5, 500.20);

顺便说一句，你在这里也有语法错误：

acct[--num].deposite(DepositMoney);

看起来像是一个简单的拼写错误：

acct[--num].deposit(DepositMoney);

而且......有很多问题......例如：

acct[--num].withdraw(WithdrawMoney);                                    //MUST --num in order to account for 0
System.out.println("User # " + num + " funds after withdraw: " + acct[--num].getBalance() + "$");
System.out.println("User # " + num + " funds after interest: " + acct[--num].addInterest() + "$");

重复的--num索引在这里发生了什么？我严重怀疑你真的想减少那里的索引变量。我怀疑这更接近你真正想要的（num而不是所有--num）：

acct[num].withdraw(WithdrawMoney);                                    //MUST --num in order to account for 0
System.out.println("User # " + num + " funds after withdraw: " + acct[num].getBalance() + "$");
System.out.println("User # " + num + " funds after interest: " + acct[num].addInterest() + "$");

无论如何，这有点难以辨别。代码有几个问题，通过问题答案调试不太实用。

Answer 2

这一行

acct[--num].withdraw(WithdrawMoney);

有问题。如果用户输入数字 0 怎么办？然后num将等于 0 ，＆amp;你会得到一个ArrayIndexOutOfBoundsException。（除了 @Janos 所说的）

由于您从 1 开始初始化帐号，您应该检查用户是否输入 0 ，＆amp;相应地采取行动。

将参数输入到对象数组中？

2 个答案: