java如何读取文本文件中的字符串并提取单个字符？"0"

3 月，1 周 Questions & Answers 81

如何请求字符串输入，然后提取0字符？我使用的是“fstream.next（）”，它可以输入任何内容，而不仅仅是字符串。我只需要一个字符，我以后可以在循环中使用它，程序只接受T、D和E的字符输入

然后程序读取双精度。然后程序用参数（char，double）调用实例方法。实例方法稍后会执行它的操作并保存输入。该程序稍后会返回并重新执行

目前，我收到一个错误“java.util.InputMismatchException”。如果你能提出建议，我将不胜感激！如果需要澄清，请告诉我。提前谢谢！：）

这是我的代码：

    /** holds answer of whether user has more inputs or not */
    String answer;
    /** holds the results when calling inLetter() */
    char letter;
    /** holds the results when checking for types/strings in txt file */
    String inType = "";
    /** holds double results when searching line by line the text file */
    double inAmount = 0;
    /** holds the results when calling inAmount() */
    double amount;
    /** initiates infile to null */
    File infile = null;
    /** count system for how many valid lines were read and used */
    int count = 0; 

    /** calls description method */
    description();
    /** initiates new Object */
    GironEventClass newInput = new GironEventClass();
    try{
        /** defines new variable linked to .dat file */
        infile = new File("GironEvent.dat");
        /** calls fstream scanner - for use on file */
        Scanner fstream = new Scanner(infile);

        /** calls while loop. As long as there is a line, the loop continues */
        while(fstream.hasNext())
        {
            /** inputs first string in line of file to variable inType */
            inType = fstream.nextLine();
            char a_char = inType.charAt(0);

            /** inputs first int in line of file to variable inAmount */
            inAmount = fstream.nextDouble();

            try{
                /** calls instance method with two parameters */
                newInput.donations(a_char, inAmount);
                /** count ticket increases */
                count+=1;

            }
            catch(IllegalArgumentException a){
                /** prints out error if exception is caught*/
                System.out.println("Just caught an illegal argument exception. ");
            }  

            }
        /** closes stream between program and fiel */
        fstream.close();

        /** outputs line count, and totals per type */
        System.out.println("\n" + count + " number of valid lines were read!\n");
        System.out.println("Total Sales: " + newInput.getSale());
        System.out.println("Donations: " + newInput.getDonated());
        System.out.println("Expenses: " + newInput.getExpenses());   
    }

    catch (FileNotFoundException e){
        /** Outputs error if file cannot be opened. */
        System.out.println("\nGironEvent.dat could not be opened. ");
    }

    do{
        /** loop asks user if there is more that needs to be added to the totals. N exits loop. */
        System.out.print("\nAre there any more items to add that were not in the text file? (Type 'Y' or 'N'): ");
        answer = keyboard.next();
        if (("Y".equals(answer)) || ("y".equals(answer)))
        {
            letter = inLetter();
            amount = inAmount();

            newInput.donations(letter, amount);
        }

    }while (("Y".equals(answer)) || ("y".equals(answer)));
    /** calls instance method to display totals in a fancy manner */
    newInput.display();
}

/** inLetter - displays types to user. Asks user to input type. Converts input into uppercase letter.
 * 
 * @return resultTwo - Uppercase form of result. Result is the type the user inputted.
 */
public static char inLetter(){
    Scanner keyboard = new Scanner(System.in);
    String result;
    String resultTwo;

    System.out.println("T = Tiket Sales");
    System.out.println("D = Donations");
    System.out.println("E = Expenses");
    System.out.print("Please input an identifier ");
    result = keyboard.nextLine();
    resultTwo = result.toUpperCase();

    return resultTwo;    
}

/** inAmount - asks user for amount. Tests that amount isn't a negative number or a zero.
 * 
 * @return result - the amount the user inputed. regardless if it was the first or tenth time. 
 */
public static double inAmount(){
    Scanner keyboard = new Scanner(System.in);
    double result;

    System.out.println("Please input an amount ");
    result = keyboard.nextDouble();

    if(result <= 0){
        System.out.print("Please input a positive and non-zero amount ");
        result = keyboard.nextDouble();
    }

    return result;
}
/** description - displays a description of what the program does
 * void.
 */
public static void description(){
    System.out.println("The program will ask you what amount is being spent on what.");
    System.out.println("    ex: expenses, ticket sales, and profts.");
    System.out.println("This program will help determine whether the event generated or lost money.");      
}

我需要以下街区的帮助：

 /** inputs first string in line of file to variable inType */
            inType = fstream.nextLine();
            char a_char = inType.charAt(0);

            /** inputs first int in line of file to variable inAmount */
            inAmount = fstream.nextDouble();

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java如何读取文本文件中的字符串并提取单个字符？"0"

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