java - 变量未在本地读取错误。不明白为什么

Question

我正在做一项学校作业。该程序要求用户提供文件名，并计算该文件中的字符数、单词数和行数。然后询问下一个文件的名称。当用户输入不存在的文件时，程序会打印所有已处理文件中存在的字符、单词和行的总数。

所以我编写了该程序，但出现了一些错误。这是计数器程序，我在线收到错误

private FileCounter counter; 

和

private boolean done;

错误提示:FieldCounter.done 永远不会在本地读取。前一行也是如此。我不明白为什么我会收到这个警告。

程序的其余部分:

    import java.util.Scanner;
    import java.io.FileReader;
    import java.io.FileNotFoundException;
    /**
    * A class to count the number of characters, words, and lines in files.
    */

    public class FileCounter
    {
       /**
          Constructs a FileCounter object.
       */
       public FileCounter()
       {
        words = 0;
        lines = 0;
        chars = 0;
        input = "";

     }

       /**
          Processes an input source and adds its character, word, and line
          counts to this counter.
          @param in the scanner to process
       */
       public void read(Scanner in) throws FileNotFoundException
       {

           boolean done = false;
           while (!done)
           {
                 while(in.hasNextLine())
                 {
                   lines++;
                   words++;
                   int j = 0;
                   file = in.nextLine();
                   input = input + file;
                   for(int i = 1; i < file.length(); i++)
                   {
                   if(file.substring(j, i).equals(" "))
                   {
                     words++;
                   }


                   j++;

                }
                  }
                   char[] array = input.toCharArray();
                   int num = array.length;
                   chars += num;
                   if(in.hasNextLine() == false)
                   done = true;
                }



      }
      /**
          Gets the number of words in this counter.
          @return the number of words
       */
       public int getWordCount()
       {
         return words;
      }

       /**
          Gets the number of lines in this counter.
          @return the number of lines
       */
       public int getLineCount()
       {    
          return lines;
       }    

       /**
          Gets the number of characters in this counter.
          @return the number of characters
       */
       public int getCharacterCount()
       {

           return chars;
       }

       private String input;
       private int words;
       private FileCounter counter;
       private int lines;
       private boolean done;
       private int chars;
       private String file;

    }


import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.Scanner;

/**
   This class prints a report on the contents of a number of files.
*/
public class FileAnalyzer
{
   public static void main(String[] args) 
   {  
      Scanner in = new Scanner(System.in);
      FileCounter counter = new FileCounter();
      boolean more = true;
      while (more)
      {
         System.out.print("Please enter the next filename, or <Enter> to quit: ");
         String filename = in.nextLine();
         if (filename.length() > 0)
         {
             try
             {
                 FileReader fileRead = new FileReader(filename);
                 Scanner fileInput = new Scanner(fileRead);
                 counter.read(fileInput);
             }
             catch (FileNotFoundException fnfe)
             {
                 System.out.println("File " + filename + " was not found: " + fnfe);
             }
         }
         else
         {
           more = false;
         }
      }
      System.out.println("Characters: " + counter.getCharacterCount());
      System.out.println("Words: " + counter.getWordCount());
      System.out.println("Lines: " + counter.getLineCount());
   }
}

Answer 1

您有一个私有(private)成员变量done，它从未被赋值。大概是因为您在 read 方法中声明了一个局部变量 done 并使用了它。 这是一个与 FileCounter.done 完全独立的变量，因此永远不会使用 FileCounter.done。

更改:

boolean done = false;

简单地说:

done = false;

您不再创建单独的局部变量，而是使用类的成员变量。

或者，删除 private boolean done; 以删除成员变量，但是 - 如果您这样做 - 请记住 done 是一个局部变量，并且不会在多次调用 read 时保留其值(在本例中这可能是您想要的，但理解其中的区别很重要)。