Question

我是一名新的Java学生，我正在编写一个程序，该程序包含一个main方法，一个类文件，两个输入.txt文件和一个output.txt文件。主要方法应询问用户帐户余额和年度利息是什么，并从各自的文件中导入存取款信息，然后在输出文件中显示类文件中的所有计算。我最初写这个文件是为了让用户使用扫描仪询问所有这些输入，现在我正试图让它使用文件作为输入工作...这不是很好。

主要方法：

    import java.util.Scanner;
    import java.io.*;
    public class SavingsAccountDemo {

   public static void main(String[] args) {
   //declare variables
   double interest;
   double startAmount;
   double amountDeposit;
   double amountWithdraw;
   double d, w;
   String filenameInputW, filenameInputD, filenameOutput;
   PrintWriter oFile;
   File wFile, dFile;
   Scanner iFile;

   Scanner key = new Scanner(System.in);

    //get initial balance
   System.out.println("Enter initial account balance: ");
   startAmount = key.nextDouble();

   //create SavingsAccount class object sending starting amount to constructor
   SavingsAccount money = new SavingsAccount(startAmount);

   //get annual interest rate
   System.out.println("Enter annual interest rate: ");
   interest = key.nextDouble();

   //send interest rate to class
   money.setInterest(interest);

   //Retrieve withdrawals from withdrawal.txt
   filenameInputW="withdrawal.txt";
   wFile = new File (filenameInputW);
   iFile = new Scanner (wFile);
   while(iFile.hasNext())
   {
        double num;

        num=iFile.nextDouble();
        amountWithdraw += num;

        if(amountWithdraw >= 0.1)
        w++;
   }

   //send to SavingsAccount class
    money.withdraw(amountWithdraw);

   //Retrieve deposits from deposit.txt
   filenameInputD="deposit.txt";
   dFile = new File (filenameInputD);
   iFile = new Scanner (dFile);

   while(iFile.hasNext())
   {
        double num;

        num=iFile.nextDouble();
        amountDeposit += num;

        if (amountDeposit >= 0.1)
        d++;
   }

   //send to SavingsAccount class
    money.deposit(amountDeposit);

   //display retults
   filenameInputW="output.txt";
   oFile=new PrintWriter (filenameOutput);
   oFile.println("The ending balance is: " + money.getBalance());
   oFile.println("The total amount of withdrawls are: " + w);
   oFile.println("The total amount of deposists are: " + d);
   oFile.println("The annual interest rate is: " + money.getInterest());

}

}

我的班级文件

/**
 * @(#)SavingsAccount.java
 *
 *
 * @author 
 * @version 1.00 2013/5/6
 */


public class SavingsAccount {

        //variables
        private double interest;
        private double balance;


        //Constructor
        public SavingsAccount(double b)
        {
            balance = b;
            interest = 0.0;
        }

        //Accessors
        public void setInterest(double i)
        {
            interest = i;
        }

        public void setBalance(double b)
        {
            balance = b;
        }

        //Mutators
        public double getInterest()
        {
            return interest;
        }

        public double getBalance()
        {
            return balance;
        }

        //Withdraw method
        public void withdraw(double withdraw)
        {
            balance = balance - withdraw;
        }

        //Deposit method
        public void deposit(double deposit)
        {
            balance = balance + deposit;
        }


        //Adding monthly interest to the balance
        public void addInterest()
        {
            double x = ((interest/12) * balance);
            balance = balance + x;
        }

}

我收到这些错误：

--------------------Configuration: --------------------
C:\Users\Home\Documents\JCreator Pro\MyProjects\SavingsAccount\src\SavingsAccountDemo.java:43: error: variable amountWithdraw might not have been initialized
            amountWithdraw += num;
            ^
C:\Users\Home\Documents\JCreator Pro\MyProjects\SavingsAccount\src\SavingsAccountDemo.java:46: error: variable w might not have been initialized
            w++;
            ^
C:\Users\Home\Documents\JCreator Pro\MyProjects\SavingsAccount\src\SavingsAccountDemo.java:50: error: variable amountWithdraw might not have been initialized
        money.withdraw(amountWithdraw);
                       ^
C:\Users\Home\Documents\JCreator Pro\MyProjects\SavingsAccount\src\SavingsAccountDemo.java:62: error: variable amountDeposit might not have been initialized
            amountDeposit += num;
            ^
C:\Users\Home\Documents\JCreator Pro\MyProjects\SavingsAccount\src\SavingsAccountDemo.java:65: error: variable d might not have been initialized
            d++;
            ^
C:\Users\Home\Documents\JCreator Pro\MyProjects\SavingsAccount\src\SavingsAccountDemo.java:69: error: variable amountDeposit might not have been initialized
        money.deposit(amountDeposit);
                      ^
C:\Users\Home\Documents\JCreator Pro\MyProjects\SavingsAccount\src\SavingsAccountDemo.java:73: error: variable filenameOutput might not have been initialized
       oFile=new PrintWriter (filenameOutput);
                              ^
C:\Users\Home\Documents\JCreator Pro\MyProjects\SavingsAccount\src\SavingsAccountDemo.java:75: error: variable w might not have been initialized
       oFile.println("The total amount of withdrawls are: " + w);
                                                              ^
C:\Users\Home\Documents\JCreator Pro\MyProjects\SavingsAccount\src\SavingsAccountDemo.java:76: error: variable d might not have been initialized
       oFile.println("The total amount of deposists are: " + d);
                                                             ^
C:\Users\Home\Documents\JCreator Pro\MyProjects\SavingsAccount\src\SavingsAccountDemo.java:37: error: unreported exception FileNotFoundException; must be caught or declared to be thrown
       iFile = new Scanner (wFile);
               ^
C:\Users\Home\Documents\JCreator Pro\MyProjects\SavingsAccount\src\SavingsAccountDemo.java:55: error: unreported exception FileNotFoundException; must be caught or declared to be thrown
       iFile = new Scanner (dFile);
               ^
C:\Users\Home\Documents\JCreator Pro\MyProjects\SavingsAccount\src\SavingsAccountDemo.java:73: error: unreported exception FileNotFoundException; must be caught or declared to be thrown
       oFile=new PrintWriter (filenameOutput);
             ^
12 errors

Process completed.

我不是在寻找讲义，这是我在这里的第一篇求助文章，但我知道你们不会为我解决这个问题......我只需要学习如何正确地做到这一点。我只是不知道为什么初始化有问题（所有提到的变量都被初始化）并且文件位于同一个文件夹中。

Answer 1

从您的代码中，您可以在最顶层写下以下内容：double amountWithdraw;就是这样。这不是初始化，而是声明。

如果你的女朋友开始谈论孩子，这同样适用，对吗？如果她宣称“我想要孩子”，那就像她“初始化”（生下）一个孩子一样。两者可能同样有压力，但方式不同。

您需要键入double amountWithdraw = 0.0;或在修改值之前添加以下内容：amountWithdraw = 0.0;。这将解决你的一小部分问题。

Answer 2

编辑：对于错误......

在声明它们时，您应该给出这些变量值。即int w = 0等。

肮脏的快速修复：至于其他与异常相关的错误，为简单起见，您可以放置public static void main(String[] args) throws FileNotFoundException以便在过渡期间使用。

正确修复：通常情况下，应该在catch块中处理FileNotFoundException，因为在willy-nilly重新抛出异常不是好习惯

Answer 3

--------------------配置：-------------------- C：\ Users \ Home \ Documents \ JCreator Pro \ MyProjects \ SavingsAccount \ src \ SavingsAccountDemo.java：43：错误：变量amountWithdraw可能尚未初始化 amountWithdraw + = num;

好吧，你声明变量amountWithdraw为double，但是compilator不知道这个变量的值是什么，他不能添加num。所以声明后你需要初始化amountWithdraw。它可以是这样的：

amountWithdraw = 0;

这很简单。

Answer 4

我认为您对初始化和声明之间的区别感到困惑。确实提供了产生错误的变量，但它们没有初始值。

看看w++。这意味着：向w添加1。但是什么是w？你没有定义它。

同样的问题适用于d，amountWithdraw和amountDeposit

此外，具有文件作为输入的新扫描程序需要FileNotFoundException的try-catch语句。

最后，我认为您的意思是filenameOutput="output.txt";而不是filenameInputW="output.txt";

初始化和FileNotFoundException错误

4 个答案: