Question

我在阅读第一个文件并翻译它或写入新文件时遇到了Java程序的问题。

以下是名为'transactions.txt'的第一个文本文件中的输入：

Joe Turing, 4124.50 D 200
Charles Babbage, 300.00 D 100
Sam Backus, 350.25 W 51
Sam Hopper, 600.50 X 600
Robert McCarthy, 1000.00 R 0
Jack Atanasoff, 200.00 W 200
Anne Stroustrup, 300.75 W 301
Amanda Hollerith, 500.00 W 2

我正在写一个名为“output.txt”的文件。我可以让我的程序读取和写入上面的第一行或上面的第二行。我需要它来写所有行。

import java.io.FileInputStream;
import java.io.FileNotFoundException;
import java.io.FileOutputStream;
import java.io.PrintWriter;
import java.util.Scanner;


public class TranactionValidator {

    public static void main(String[] args) {
        // TODO Auto-generated method stub
        Scanner fileIn = null;
        PrintWriter fileOut = null;

        try {   
            fileIn = new Scanner(new FileInputStream("transactions.txt"));
        }
        catch (FileNotFoundException e) {
            System.out.print("Input file not found!!");
            System.exit(0);
        }
        try {
            fileOut = new PrintWriter(new FileOutputStream("output.txt"));
        }
        catch (FileNotFoundException e) {
            System.out.println("Cannot create file!");
            System.exit(0);
        }

        while (fileIn.hasNextLine()) {
            String firstName = fileIn.nextLine();
            String lastName = fileIn.nextLine();
            double beforeTransaction = fileIn.nextDouble();
            String transactionType = fileIn.nextLine();
            int transactionAmount = fileIn.nextInt();



            fileOut.println(lastName + " " +firstName);
            fileOut.println("Before Transaction: " + beforeTransaction);
            fileOut.println("Transaction Type: " + transactionType);

            if (transactionType.equals("W") || transactionType.equals("D") || transactionType.equals("R")){
                switch (transactionType) {
                case "W":
                    fileOut.println("Transaction Amount: " + transactionAmount);
                    if (transactionAmount <= -1) {
                        double afterTransactionW = beforeTransaction - transactionAmount;
                        fileOut.println("After Transaction: " + afterTransactionW);
                        if (afterTransactionW < 300.00) {
                            fileOut.println("Warning! Account balance below $300.00");
                        }
                    }
                    else {
                        fileOut.println("Number must be positive");
                    }
                    break;
                case "D":
                case "d":
                    fileOut.println("Transaction Amount: " + transactionAmount);
                    if (transactionAmount <= -1) {
                        double afterTransactionD = beforeTransaction + transactionAmount;
                        fileOut.println("After Transaction: " + afterTransactionD);
                        if (afterTransactionD < 300.00) {
                            fileOut.println("Warning! Account balance below $300.00");
                        }
                    }
                    else {
                        fileOut.println("Number must be positive");
                    }
                    break;
                case "R":
                case "r":
                    fileOut.println("Transaction Amount: " + transactionAmount);
                    if (transactionAmount <= -1) {
                        double afterTransactionR = beforeTransaction;
                        fileOut.println("After Transaction: " + afterTransactionR);
                        if (afterTransactionR < 300.00) {
                            fileOut.println("Warning! Account balance below $300.00");
                        }
                    }
                    else {
                        fileOut.println("Number must be positive");
                    }
                    break;
                default:
                    fileOut.println("After Transaction: Error");
                    break;
                }
            }
            else {
                fileOut.println("Must enter a code such as W, R, and D");
            }

            fileOut.println("------------------------------------------------------------------------");
            fileOut.close();
        }

        fileIn.close();
        System.exit(0);

    }
}

当我运行程序时，我会在控制台中抛出这个之前得到几个“无法创建文件!!”：

   Exception in thread "main" java.util.InputMismatchException
      at java.util.Scanner.throwFor(Unknown Source)
      at java.util.Scanner.next(Unknown Source)
      at java.util.Scanner.nextDouble(Unknown Source)
      at TranactionValidator.main(TranactionValidator.java:34)

有人能指出我正确的方向吗？

Answer 1

错误InputMismatchException的原因是您尝试分配给String以及double和int这条线：

        String firstName = fileIn.nextLine();
        String lastName = fileIn.nextLine();
        double beforeTransaction = fileIn.nextDouble();// line 34
         ...

但你可以试试这样的事情：

        while (fileIn.hasNextLine()) {
        String[] arr = fileIn.next().split(" ");

        String firstName = arr[0];
        String lastName = arr[0];
        double beforeTransaction = Double.parseDouble(arr[0]);
        String transactionType = arr[0];
        int transactionAmount = Integer.parseInt(arr[0]);

Java - 不写入文件

1 个答案: