爪哇识别令牌

Question

我正在做一个任务，我必须查看一个文件并识别令牌。我想我正走在正确的轨道上。我大部分工作正常，但我无法识别特定字符，因此在识别令牌时我可以选择忽略它。它的一个\n我已经得出这个结论，因为当我在if语句中尝试tokens.get(6).equals('\n')时，它会出现错误，因为它不是\n我无法识别存储在此数组索引值处的内容。该文本文件看起来像这样

编辑：我知道它\n因为我做System.out.println("ddd" + tokens.get(6) +"dddd")输出功率为ddd则新行，并dddd

编辑2：我添加的System.out.println（” unidenfified “+词）;这是输出

read a 
read b 
c := a + b + 3 
write c 

输出应该是这个

<read>, read 
<id>, a 
<read>, read 
<id>, b 
<id>, c 
<assign>, := 
<id>, a 
<add_op>, + 
<id>, b 
<add_op>, + 
<number>, 3 
<write>, write 
<id>, c 

我看起来就像这样

<read>, read 
<error>, unidenfified 
<error>, unidenfified 
<assign>, := 
<id>, a 
<add_op>, + 
<id>, b 
<add_op>, + 
<error>, unidenfified 
<error>, unidenfified 

我不知道为什么会这样。 我的代码：

import java.util.ArrayList; 
import java.util.Scanner; 
import java.io.*; 
import java.lang.Character; 

public class Tokens { 

    public static void main(String[] args) throws IOException { 

     Scanner input = new Scanner(System.in); // Scanner for taking input from 
               // the user 

     String fileName; 
     System.out.println("Enter the name of the file."); 
     fileName = input.next(); 

     fileExists(fileName); // Checks to see if the file exists 

     ArrayList<Character> arrayOfTokens = new ArrayList<Character>(); 
     ArrayList<String> assembled = new ArrayList<String>(); 
     readToArray(arrayOfTokens, fileName); 
     assembled = assembleTokens(arrayOfTokens); 

     for(int i = 0; i < assembled.size(); i++) { 
      analyze(assembled.get(i)); 
     } 

    } 

    /* 
    * readToArray goes through a file and adds all its elements in individual 
    * character form. It is stored into an arraylist and it is then returned 
    * 
    * @param storeChar: This is an arraylist of characters that the characters 
    * will be saved into and then returned. 
    * 
    * @param fileName: The filename that you want to take the data from. 
    */ 
    private static ArrayList<Character> readToArray(
      ArrayList<Character> storeChar, String fileName) throws IOException { 
     /* 
     * Block of code to setup the fileInput stream to take in data from the 
     * file. Reads character by character and stores into an arraylist. int 
     * atChar: the current character the reader is at. Returns in int format 
     * (Need to be converted to character later on) int currentIndex: to add 
     * a character to an index. Increments until no more characters are left 
     */ 
     FileInputStream fileInput = new FileInputStream(fileName); 
     int atChar; 
     int currentIndex = 0; 

     /* 
     * Loop to go through and add the converted character from an int to the 
     * arraylist. Loops until atChar returns -1 which means no more 
     * characters in file. 
     */ 
     while ((atChar = fileInput.read()) != -1) { 
      storeChar.add(currentIndex, (char) (atChar)); 
      currentIndex++; 
     } 
     fileInput.close(); 

     return storeChar; 
    } 

    /* 
    * fileExists method makes sure the file the user enters exists in the 
    * system. If it doesn't then the program will terminate before any further 
    * code is executed. 
    * 
    * @param fileName: Takes in a string paramater of the file name that you 
    * want to if it exists. 
    */ 
    private static void fileExists(String fileName) { 

     boolean ifExists; // Boolean statement that will later be set to the 
          // value of whether the file exists or not 

     File file = new File(fileName); 
     ifExists = file.exists(); 

     if (ifExists == false) { 
      System.out 
        .println("Unable to find the file. Will now close the program."); 
      System.exit(0); 
     } 
    } 

    private static ArrayList<String> assembleTokens(ArrayList<Character> tokens) { 

     ArrayList<String> identified = new ArrayList<String>(); 
     int counter = 0; 
     String concatinated = ""; 

     while (counter < tokens.size()) { 
      if (!tokens.get(counter).equals(' ')) { 
       concatinated += tokens.get(counter); 
       counter++; 
      } else { 
       identified.add(concatinated); 
       concatinated = ""; 
       counter++; 
      } 
     } 

     return identified; 
    } 

    private static void analyze(String word) { 
     if(word.equals("read")) { 
      System.out.println("<read>, read"); 
     } else if(word.equals("write")) { 
      System.out.println("<write>, write"); 
     } else if(word.equals(":=")) { 
      System.out.println("<assign>, :="); 
     } else if(word.equals("(")) { 
      System.out.println("<lparen>, ("); 
     } else if(word.equals(")")) { 
      System.out.println("<rparen>,)"); 
     } else if(word.equals("+") || word.equals("-")) { 
      System.out.println("<add_op>, " + word); 
     } else if(word.equals("*") || word.equals("/") || word.equals("//") || word.equals("%")) { 
      System.out.println("<mult_op>, " + word); 
     } else if(word.matches("[a-z]+[A-Za-z0-9]*")) { 
      System.out.println("<id>, " + word); 
     } else if(word.matches("\\d+(\\.\\d+)?")) { 
      System.out.println("<number>, " + word); 
     } else { 
      System.out.println("<error>, unidenfified"); 
     } 

    } 
} 

Answer 1

文件

if (atChar != '\n') { 
    storeChar.add(currentIndex, (char) (atChar)); 
} 

或者在阅读时只需滤除\n你可以使用

fileInput.readLine() 

，然后记号化字符串

编辑

有了上次编辑后一看，如果会更好做readLine，然后使用String.split(" ");让您的令牌