java - Java中的流、缓冲区

Question

我有java考试，当我学习时，我看到了这个练习，我尝试解决它，但我发现一些困难，所以请帮助我考虑实用程序中方法的以下注释、 header 和部分代码名为 Atbash 的加密类。

    /**
    * Prompts the user for the pathname of a source .txt file to encrypt.
    * Prompts the user for the pathname of a destination .txt file
    * to which the encrypted text will be written.
    * The pathnames are then used to create two File objects.
    * The method then attempts to open streams on both files, one to
    * read from the source file, the other to write to the destination file.
    *
    * The method then reads from the read stream a line at a time.
    * Each line read is converted to uppercase using the message
    * toUpperCase(). The method then constructs an encrypted string
    * into which all the alphabetic characters from the line are
    • substituted by their atbash equivalent, however any numeric or
    * punctuation characters are simply added unchanged to the encrypted
    * string. After each string is constructed it is written to the write
    * stream followed by a newline character.
    */
    public static void encryptFile()
    {
    OUDialog.alert("Please choose a file to encrypt");
    String pathname = OUFileChooser.getFilename();
    File aFile = new File(pathname);
    OUDialog.alert("Please give a file name for the encrypted file");
    String pathname2 = OUFileChooser.getFilename();
    File bFile = new File(pathname2);
    BufferedReader bufferedFileReader = null;
    BufferedWriter bufferedFileWriter = null;

    try
    {
    String currentLine;
    bufferedFileReader = new BufferedReader(new FileReader(aFile));
    bufferedFileWriter = new BufferedWriter(new FileWriter(bFile));
    String codedLine = "";
    char currentChar;
    String alphabet ="ABCDEFGHIJKLMNOPQRSTUVWXYZ";
    String mirror ="ZYXWVUTSRQPONMLKJIHGFEDCBA";
    currentLine = bufferedFileReader.readLine();
    while (//Boolean condition to be written as your answer for part (i))
/**this what I do while(currentLine!=null)*/

    {
    //Statement block to be written as your answer for part (ii)

    }
    }
    catch (Exception anException)
    {
    System.out.println("Error: " + anException);
    }
    finally
    {
    try
    {
    //Statement block to be written as your answer for part (iii)
  /* bufferedFileReader.close();
   *  bufferedFileWriter.close();
   */

    }
    catch (Exception anException)
    {
    System.out.println("Error: " + anException);
    }
    }
    }

(i) 写出上述方法中 while 循环的 boolean 条件。

while(currentLine= bufferedFileReader.readLine()!= null)
    {

    }

(ii) 编写上述方法中 while 语句 block 的代码。这应该确保当 while 循环终止时，目标 .txt 文件包含源 .txt 文件的加密版本。您的代码应该使用变量 bufferedFileReader、bufferedFileWriter、currentLine、codedLine、currentChar、字母表和镜像。您可能会发现 String 协议(protocol)中的以下两条消息很有用:charAt(int) 返回参数指定索引处的 char 值和indexOf(char)返回第一次出现的索引接收者内部的争论。

(iii) 编写最后一个 try block 的代码。

bufferedFileReader.close();
 bufferedFileWriter.close();

Answer 1

这里

/**this what I do while(currentLine!=-1)*/

由于 currentLine 是 String，因此您无法将其与 int 值进行比较。您应该检查 BufferedReader.readLine() 的 Javadoc查看它如何指示没有更多数据可供读取，然后相应地修复该情况。