如果银行账户类中遗漏了对帐单？

Question

我在使用以下语法时遇到了一些问题。

我目前正在学习 Java，并且一直在通过过去的试卷来帮助建立我的 Java 知识。

问题来了：

编写一个 Account 类，其中包含帐号和当前余额的实例变量。实现构造函数和方法 getAccountNumber()、getBalance()、debit(double amount) 和 credit(double amount)。在您的借记卡和贷记卡实现中，检查指定金额是否为正数，以及在借记卡方法中不会导致透支。在这些情况下返回 false。否则，更新余额。

我已经尝试过这样做，但是，我还没有为借方和贷方方法实现布尔函数。我只是想先构建程序并尝试让它工作。之后我打算看看这个，因为我不确定如何返回 true 或 false，同时还试图从上述方法返回一个金额。

由于我还在学习 Java，请原谅我的代码中的任何错误。

我可以运行我的代码，但是当我输入存款时，它似乎无法正常工作，我将不胜感激。

这是我的代码：

import java.util.*;

public class Account {

private int accountNumber;
private static double currentBalance;
private static double debit;

// ***** CONSTRUCTOR *****//
public Account(double currentBalance, int accountNumber) {
    accountNumber = 12345;
    currentBalance = 10000.00;
}

public int getAccountNumber(int accountNumber) {
    this.accountNumber = accountNumber;
    return accountNumber;
}

public double getcurrentBalance(double currentBalance) {
    this.currentBalance = currentBalance;
    return currentBalance;
}

public static double debit(double currentBalance, double amount) {
    currentBalance -= amount;
    return currentBalance;
}

public static double credit(double currentBalance, double amount) {
    currentBalance += amount;
    return currentBalance;
}

public static void main(String [] args){
    String withdraw = "Withdraw";
    String deposit = "Deposit";
    double amount;
    Scanner in = new Scanner(System.in);
    System.out.println("Are you withdrawing or depositing? ");
    String userInput = in.nextLine();
    if(userInput == withdraw)
        System.out.println("Enter amount to withdraw: ");
        amount = in.nextDouble();
            if(amount > currentBalance)
                System.out.println("You have exceeded your amount.");

                debit(currentBalance, amount);

            System.out.println("Your new balance is: " + currentBalance);

            if (userInput == deposit)
                System.out.println("Enter amount to deposit: ");
                    amount = in.nextDouble();
                    credit(currentBalance, amount);

        System.out.println("Your new balance is: " + currentBalance);

}
}

再次请原谅我的代码中的任何错误。我还在学习它的语法。

Answer 1

在 if 语句 if(userInput == withdraw) 中，您尝试比较 String 对象。

在 Java 中比较 String 对象时使用 equals 方法而不是比较运算符 ==

if(userInput.equals(withdraw))

代码中有几个实例使用== 比较String 对象，将它们更改为使用equals。

此外，当使用条件块时，最好用大括号将块括起来{}

if(true){

}

Answer 2

您不使用方括号，因此仅执行 if 语句后的第一行。此外，应使用.equals(otherString) 比较字符串。像这样：

if(userInput.equals(withdraw))
    System.out.println("Enter amount to withdraw: "); //Only executed if userInput == withdraw
    amount = in.nextDouble(); //Always executed

if(userInput.equals(withdraw)) {
    System.out.println("Enter amount to withdraw: "); 
    amount = in.nextDouble(); 
    //All executed
}

这样做：

if(userInput.equals(withdraw)) {
    System.out.println("Enter amount to withdraw: ");
    amount = in.nextDouble();
    if(amount > currentBalance)
            System.out.println("You have exceeded your amount.");

    debit(currentBalance, amount);
    System.out.println("Your new balance is: " + currentBalance);
}

if (userInput.equals(deposit)) {
     System.out.println("Enter amount to deposit: ");
     amount = in.nextDouble();
     credit(currentBalance, amount);
     System.out.println("Your new balance is: " + currentBalance);
}

请注意，如果您的提款金额超过当前余额，您将收到“警告消息”，但您的提款将继续。因此，您最终会得到一笔负数的钱。如果您不想这样做，则必须相应地进行更改。但是，这种方式显示了使用括号（或不使用括号）如何产生不同的效果。

Answer 3

if (userInput == deposit)

应该是

if (userInput.equals(deposit))

提现也一样。

Answer 4

关于这些方法：

public static double debit(double currentBalance, double amount) {
    currentBalance -= amount;
    return currentBalance;
}

public static double credit(double currentBalance, double amount) {
    currentBalance += amount;
    return currentBalance;
}

函数的输入实际上不应该包括当前余额，对象已经知道当前余额是什么（它保存在对象 currentBalance 字段中，正如已经指出的那样，它不应该是静态的）。

想象一台真正的提款机，其行为如下：

Whats my current balance:
£100
CreditAccount("I promise my current balance is £1 Million, it really is", £10):
Balance:£1,000,010

编辑：包含这样行为的代码

import java.util.*;

public class Account {

private int accountNumber;
private double currentBalance; //balance kept track of internally

// ***** CONSTRUCTOR *****//

    public Account(int accountNumber, double currentBalance) {
        this.accountNumber = accountNumber;
        this.currentBalance = currentBalance;
    }


    public int getAccountNumber() {
        return accountNumber;
    }

    public double getcurrentBalance() {
        return currentBalance;
    }

    public boolean debit(double amount) {
        //we just refer to the objects fields and they are changed

        if (currentBalance<amount){
            return false; //transaction rejected
        }else{
            currentBalance -= amount;
            return true;
            //transaction approaved and occured
        }

        //Note how I directly change currentBalance, there is no need to have it as either an input or an output

    }

    public void credit( double amount) {
        //credits will always go through, no need for return boolean
        currentBalance += amount;

        //Note how I directly change currentBalance, there is no need to have it as either an input or an output
    }

    public static void main(String [] args){
        Account acc=new Account(1234,1000);

        acc.credit(100);

        System.out.println("Current ballance is " + acc.getcurrentBalance());

        boolean success=acc.debit(900); //there is enough funds, will succeed

        System.out.println("Current ballance is " + acc.getcurrentBalance());
        System.out.println("Transaction succeeded: " +  success);


        success=acc.debit(900); //will fail as not enough funds

        System.out.println("Current ballance is " + acc.getcurrentBalance());
        System.out.println("Transaction succeeded: " +  success);


    }
}

我没有打扰使用键入的输入，因为您似乎掌握了窍门

Answer 5

如果没有“{”和“}”，if 语句后的第一行只会作为该语句的一部分执行。此外，您的if (userInput == deposit) 块没有正确缩进，它不应该在if (userInput == withdraw) 之下。字符串比较应该使用userInput.equals(withdraw)

Answer 6

对于借记和贷记方式：

public static boolean debit(double currentBalance, double amount) {
   currentBalance -= amount;
   if<currentBalance < 0){
       return false
   }
   return true;
}

public static boolean credit(double currentBalance, double amount) {
   currentBalance += amount;
   if<currentBalance > 0){
       return false
   }
   return true;
}

现在我想我把布尔值弄混了。描述有点不清楚每种方法返回什么。

Answer 7

使用 equals() 方法代替 == 比较 Objetcs 的相等性而不是值

import java.util.*;

public class Account{

private int accountNumber;
private static double currentBalance;
private static double debit;

// ***** CONSTRUCTOR *****//
public Account(double currentBalance, int accountNumber) {
    accountNumber = 12345;
    currentBalance = 10000.00;
}

public int getAccountNumber(int accountNumber) {
    this.accountNumber = accountNumber;
    return accountNumber;
}

public double getcurrentBalance(double currentBalance) {
    this.currentBalance = currentBalance;
    return currentBalance;
}

public static double debit(double currentBalance, double amount) {
    currentBalance -= amount;
    return currentBalance;
}

public static double credit(double currentBalance, double amount) {
    currentBalance += amount;
    return currentBalance;
}

public static void main(String [] args){
    String withdraw = "Withdraw";
    String deposit = "Deposit";
    double amount;
    Scanner in = new Scanner(System.in);
    System.out.println("Are you withdrawing or depositing? ");
    String userInput = in.nextLine();
    if(userInput.equals(withdraw))
        System.out.println("Enter amount to withdraw: ");
        amount = in.nextDouble();
            if(amount > currentBalance)
                System.out.println("You have exceeded your amount.");

                debit(currentBalance, amount);

            System.out.println("Your new balance is: " + currentBalance);

            if (userInput .equals(deposit))
                System.out.println("Enter amount to deposit: ");
                    amount = in.nextDouble();
                    credit(currentBalance, amount);

        System.out.println("Your new balance is: " + currentBalance);

}
}