BufferedReader.readLine() 在文件开头而不是结尾处返回 null

Question

我正在为 Java 课程创建一个真/假测试，该课程将答案键和每个用户各自的答案数组存储为 BitSet。然后，这些位集被序列化为持久的顺序二进制文件，以便稍后可以由另一个应用程序对它们进行评分。

一切都很完美，除了我第一次调用 request.readLine() 时有一个奇怪的例外，这是我的 system.in inputstreamreader，用于检索用户的答案。由于某种原因，无论输入什么内容，它都会将第一个答案设置为 null，就好像它已达到 EOF 一样。

CreateTest.java（从 txt 文件读取/显示问题，收集用户答案，将其存储在 .bin 文件中）

public class CreateTest
{
private static BufferedReader request;
private static BufferedReader response;
private static String answers, userName;
private static ObjectOutputStream result;

public static void main(String[] args)
{
    response = new BufferedReader(new InputStreamReader(System.in));
    try
    {
        request = new BufferedReader(new FileReader("test.txt"));
    }
    catch(FileNotFoundException fnfe)
    {
        System.out.println("Test.txt was not found. Please fix your crappy file system.");
        System.exit(1);
    }

    System.out.println("Welcome to THE TEST\n\n" +
                        "Please respond with only \"t\" for true or \"f\" for false.\n" +
                        "This application is case-insensitive.\n" +
                        "DON'T GET EATEN BY THE GRUE!");


    System.out.println("\nPlease enter your name: ");
    try
    {
        userName = response.readLine().replaceAll("\\s", "");
        System.out.println("\n\n");
        result = new ObjectOutputStream(new FileOutputStream(userName + "TestAnswers.bin"));
    }
    catch(IOException e1) { e1.printStackTrace(); }

    try {
            for(int i=0; i<24; i++)
            {
                    System.out.println(request.readLine());
                    recordResponse();   
            }
        System.out.println("Thank you for attempting THE TEST. You probably failed.");
        result.writeObject(new BitMap(answers));
        close();

        } catch (IOException e) { e.printStackTrace(); }
}


public static void recordResponse() throws IOException
{
    String currentAnswer = response.readLine();
    //diagnostic
    System.out.println("Answer: " + answers);
    if(currentAnswer.equals("t")||
       currentAnswer.equals("T")||
       currentAnswer.equals("f")||
       currentAnswer.equals("F"))
    { answers += currentAnswer + " -- "; }
    else 
    {
        System.out.println("What, you can't read or somethin'?. Enter(case-insenstive) T or F only pal." +
                            "Try it again.");
        close();
        System.exit(1);
    }
}

public static void close() throws IOException
{
    request.close();
    response.close();
}

BitMap.java 中的相关构造函数（将传递的参数解析为 BitSets，提供按位运算）

public BitMap(String s) throws IndexOutOfBoundsException,ArithmeticException
{
    try
    {
        if(s.length() > 25) { throw new IndexOutOfBoundsException(); }
        StringTokenizer answers = new StringTokenizer(s);
        for(int i=0; i<bitString.size(); i++)
        {
            String currentToken = answers.nextToken();
            if(currentToken.equals("t") || currentToken.equals("T")) { bitString.set(i); }
            else if(currentToken.equals("f") || currentToken.equals("F")) { bitString.clear(i); }
        }
    }
    catch(IndexOutOfBoundsException ioob){System.out.println("Sorry bub, too many answers.");}
}

我对大量代码表示歉意，但我认为更多信息总比不够好。

Answer 1

您没有初始化 answers，因此它将以 null 开始。在 recordResponse 中，您在更新之前打印出 answers，因此在输入第一个答案后，您将打印 null，然后就得到了 ” nullt/f -- t/f ..."。

因此，您想要的

private static String answers = "", userName;

诊断为了相关，很可能应该在更新之后进行：

if(currentAnswer.equals("t")||
   currentAnswer.equals("T")||
   currentAnswer.equals("f")||
   currentAnswer.equals("F"))
{
  answers += currentAnswer + " -- ";
  System.out.println("Answer: " + answers);
}