java - 如何将文本文件作为字符串读取并仅提取单个字符？ "0"

Question

如何请求字符串输入，然后提取 0 字符？我使用的是“fstream.next()”，它会输入任何内容，而不仅仅是一个字符串。我只需要一个字符，稍后可以在程序仅接受 T、D 和 E 的字符输入的循环中使用它。

然后程序读取 double 。然后程序使用参数(char、double)调用实例方法。实例方法稍后执行它的操作并保存输入。程序稍后会循环回来并重新执行一遍。

目前我收到错误“java.util.InputMismatchException”。如果您能提供建议，我将不胜感激!如果需要澄清，请告诉我。先感谢您! :)

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.");      
}

我需要有关以下 block 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();

Answer 1

您的 fstream 具有 String 和 Double 的组合。

因此，当您使用 fstream.nextDouble() 时，它会抛出 java.util.InputMismatchException

引用:http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#nextDouble()

您可以首先使用 hasNextDouble() 方法检查下一个字符是否为 double

引用: http://docs.oracle.com/javase/7/docs/api/java/util/Scanner.html#hasNextDouble()