java - Java 中的数组和银行账户

Question

我正在尝试编写一个简单的银行帐户管理程序，该程序执行以下操作:

使用从用户处获取的帐号和余额并存储在数组中创建一个新帐户选择一个帐户(从数组中)删除所选帐户提款并存入所选账户。

问题:我不明白我的错误是什么。

我尝试使用不同类型的数组来存储帐号和余额，但我还没有找到答案。我在网络和 Stackoverflow 上搜索引用资料、文档、简单的示例，但找不到任何内容(我找到的那些使用了一些我还没有学过的命令和东西，所以我可以理解它们是如何工作的)。我是初学者，仍在学习中，希望得到一些建议。谢谢!

//Bank account class
public class account {
private int ANumber;
private double balance;

public account(double initialBalance, int accno) {
    balance = initialBalance;
    ANumber = accno;
}

public void deposit (double u_amm){
    balance += u_amm;
}

public double withdraw(double amount) {
    balance -= amount;
    return amount;
}

public double getBalance() {
    return balance;
}
public int getAccount(){
    return ANumber;
}
}

这是主类

 import java.util.Scanner;
 // main class
 public class bankmain {
 public static void main(String[] args) {
    Scanner scan = new Scanner(System.in);
    // Menu starts from here
    Scanner input = new Scanner(System.in);
    System.out.println("Enter the option for the operation you need:");
    System.out.println("****************************************************");
    System.out.println("[ Options: ne - New Account de - Delete Account ]");
    System.out.println("[       dp - Deposit    wi - Withdraw      ]");
    System.out.println("[           se - Select Account ex - Quit      ]");
    System.out.println("****************************************************");
    System.out.print("> ");  //indicator for user input
    String choice = input.next();
    //Options
    while(true){
  if(choice == "ne"){
    int nacc;
    int bal;
    int [][]array = new int[nacc][bal];   // Array for account and balance
    System.out.print("Insert account number: ");
    nacc =input.nextInt(); //-- Input nr for array insertion
    System.out.print("Enter initial balance: ");
    bal=input.nextInt(); //-- Input nr for array insertion
    System.out.println("Current account: " + nacc + " " +  "Balance " + bal);
    break;
  }
  // account selection      
  if(choice.equals("se")){
    System.out.println("Enter number of account to be selected: ");
    //user input for account nr from array
    System.out.println("Account closed.");
  }     
  //close account
  if(choice.equals("de")){
    //array selected for closing
    System.out.println("Account closed.");
  }
  // deposit
  if(choice.equals("dp")){
    System.out.print("Enter amount to deposit:  ");
    double amount = scan.nextDouble();
    if(amount <= 0){
        System.out.println("You must deposit an amount greater than 0.");
    } else {
        System.out.println("You have deposited " + (amount + account.getBalance()));
    }
  }
  // withdrawal     
  if(choice.equals("wi")){
    System.out.print("Enter amount to be withdrawn: ");
    double amount = scan.nextDouble();
        if (amount > account.balance()){ 
            System.out.println("You can't withdraw that amount!");
   } else if (amount <= account.balance()) {
    account.withdraw(amount);
    System.out.println("NewBalance = " + account.getBalance());
   }
   }
//quit 
if(choice == "ex"){
    System.exit(0);
        } 
    }   // end of menu loop
 }// end of main
 } // end of class

Answer 1

您的代码在很多层面上都是错误的 - 首先尝试调整您的格式和命名约定，这样您就不会养成坏习惯。不要使用小字母来命名类，尝试使用完整的单词来描述变量和字段，就像 Account.class 示例中的那样:

public class Account  {
    private Integer accountNumber;
    private Double balance;

    public Account(final Integer accountNumber, final Double initialBalance) {
        this.accountNumber = accountNumber;
        balance = initialBalance;
    }

    public Double deposit (double depositAmmount) {
        balance += depositAmmount;
        return balance;
    }

    public Double withdraw(double withdrawAmmount) {
        balance -= withdrawAmmount;
        return balance;
    }

    public Double getBalance() {
        return balance;
    }

    public Integer getAccountNumber() {
        return accountNumber;
    }
}

还尝试在所有代码中使用相同的格式(即括号后的空格)，以便您更容易阅读。

现在 - 您的应用出了什么问题:

1. 为您的帐户定义适当的持有者，即 HashMap，它将保存有关所有帐户的信息，并能够通过 accountNumber 找到它们。

   HashMap<Integer, Account> accountMap = new HashMap<Integer, Account>() ;

2. 这个应该位于 while 循环内，因为您希望用户执行多项任务。您可以省略 println，但用户必须返回到屏幕顶部才能看到选项。

   System.out.println("Enter the option for the operation you need:");
   System.out.println("****************************************************");
   System.out.println("[ Options: ne - New Account de - Delete Account ]");
   System.out.println("[       dp - Deposit    wi - Withdraw      ]");
   System.out.println("[           se - Select Account ex - Quit      ]");
   System.out.println("****************************************************");
   System.out.print("> ");  //indicator for user input
   String choice = input.nextLine();   
   System.out.println("Your choice: " + choice);
   

3. 您不应使用“==”运算符来比较字符串，因为它可能不会返回预期值。看看:How do I compare strings in Java?或What is the difference between == vs equals() in Java? 。为了安全起见，请使用对象等于，即:

   choice.equals("ne")
   

4. 没有您创建帐户的位置:

   Account newAccount = new Account(newAccountNumber, initialBalance);
   

5. 您没有使用 if-else，只是使用了 if's。它应该看起来更像这样(如果已经发现选项是“ne”，为什么要检查选项是否是“wi”):

   if(choice.equals("ne")) {
       //doStuff
   } else if choice.equals("se") {
       //doStuff
   } //and so on.
   

6. 如果您使用的 Java 版本 >= 7，那么您可以使用 switch 来代替 if-else 来比较字符串。

7. 没有错误选项的通知:

   } else {
       System.out.println("Wrong option chosen.");
   }
   

8. 您没有关闭 Scanner 对象。这在这里并不重要，因为它在 main 方法中，并且会随之关闭，但使用完后始终关闭流、数据源等是一个好习惯的问题:

   input.close(); 
   

所以整个代码可以如下所示:

import java.util.HashMap;
import java.util.Scanner;
// main class
public class BankAccount {

    public static void main(String[] args) {

        Scanner input = new Scanner(System.in);
        HashMap<Integer, Account> accountMap = new HashMap<Integer, Account>(); 

         //Options
        while(true) {

            System.out.println("Enter the option for the operation you need:");
            System.out.println("****************************************************");
            System.out.println("[ Options: ne - New Account de - Delete Account ]");
            System.out.println("[       dp - Deposit    wi - Withdraw      ]");
            System.out.println("[           se - Select Account ex - Quit      ]");
            System.out.println("****************************************************");
            System.out.print("> ");  //indicator for user input

            String choice = input.next();   
            System.out.println("Your choice: " + choice);

            if(choice.equals("ne")) {
                Integer newAccountNumber;
                Double initialBalance;
                Account newAccount;

                // Array for account and balance
                System.out.print("Insert account number: ");
                newAccountNumber = input.nextInt(); //-- Input nr for array insertion
                System.out.print("Enter initial balance: ");
                initialBalance=input.nextDouble(); //-- Input nr for array insertion
                newAccount = new Account(newAccountNumber, initialBalance);
                accountMap.put(newAccountNumber, newAccount);
                System.out.println("New Account " + newAccountNumber + " created with balance: " + initialBalance);
            }
            //select account
            else if(choice.equals("se")) {
                System.out.println("Enter number of account to be selected: ");
                Integer accountToGetNumber = input.nextInt();
                Account returnedAccount = accountMap.get(accountToGetNumber);
                if (returnedAccount != null)
                {
                    System.out.println("Account open. Current balance: " + returnedAccount.getBalance());
                }
                else
                {
                    //user input for account nr from array
                    System.out.println("Account does not exist.");
                }
            }
            //close account
            else if(choice.equals("de"))
            {
                System.out.println("Enter number of account to be selected: ");
                Integer accountToDeleteNumber = input.nextInt();
                Account removedAccount = accountMap.remove(accountToDeleteNumber);
                if (removedAccount != null)
                {
                    System.out.println("Account " + removedAccount.getAccountNumber() + " has been closed with balance: " + removedAccount.getBalance());
                }
                else
                {
                    //user input for account nr from array
                    System.out.println("Account does not exist.");
                }
            }
            // deposit
            else if(choice.equals("dp")) {
                System.out.println("Enter number of account to deposit: ");
                Integer accountToDeposit = input.nextInt();
                System.out.print("Enter amount to deposit:  ");
                double amount = input.nextDouble();
                if(amount <= 0){
                    System.out.println("You must deposit an amount greater than 0.");
                } else {
                    accountMap.get(accountToDeposit).deposit(amount);
                    System.out.println("You have deposited " + (amount));
                    System.out.println("Current balance " + accountMap.get(accountToDeposit).getBalance());
                }
            }
            // withdrawal     
            else if(choice.equals("wi")) {
                System.out.println("Enter number of account to withdraw: ");
                Integer accountToWithdraw = input.nextInt();
                System.out.print("Enter amount to withdraw:  ");
                double amount = input.nextDouble();
                if(amount <= 0) {
                    System.out.println("You must deposit an amount greater than 0.");
                } else {
                    accountMap.get(accountToWithdraw).withdraw(amount);
                    System.out.println("You have deposited " + (amount));
                    System.out.println("Current balance " + accountMap.get(accountToWithdraw).getBalance());
                }
            }
            //quit 
            else if(choice.equals("ex")) {
                break;
            } else {
                System.out.println("Wrong option.");
            } //end of if
        } //end of loop

        input.close();
    } //end of main
 } //end of class

还有很多需要改进的地方，即输入验证 - 但这应该在开始时有效。