詞法分析在Java中的字母

這個代碼分析數字和運營商只我需要它來分析字母只，並把其他事情無效我應該做些什麼細節我從教程網站得到這段代碼，並修改它，但沒有結果。詞法分析在Java中的字母

 package lexical; 

    public class Tokenizer { 


int pos; 
char[] expression; 

Tokenizer(String expression) { 
    this.expression = expression.toCharArray(); 
    this.pos = 0; 
} 

enum Type { OPERATOR, LITTER, UNKNOWN } 

class Lexeme { 
    String type, token; 
    Lexeme(String type, String token) { 
     this.type = type; 
     this.token = token; 
    } 
} 

Lexeme getNextToken() { 
    StringBuilder token = new StringBuilder(); 
    boolean endOfToken = false; 
    Type type = Type.UNKNOWN; 
    while (!endOfToken && hasMoreTokens()) { 
     while(expression[pos] == ' ' && hasMoreTokens()) 
      pos++; 
     switch (expression[pos]) { 
      case '+': 
      case '-': 
      case '*': 
      case '/': 
       if(type != Type.LITTER) { 
        type = Type.OPERATOR; 
        token.append(expression[pos]); 
        pos++; 
       } 
       endOfToken = true; 
       break; 
      case ' ': 
       endOfToken = true; 
       pos++; 
       break; 
      default: 
       if(Character.isDigit(expression[pos]) || expression[pos] == '.') { 
        token.append(expression[pos]); 
        type = Type.LITTER; 
       } else { 
        System.out.println("Systax error at position: " + pos); 
       } 
       pos++; 
       break; 
     } 
    } 
    return new Lexeme(type.name().toLowerCase(), token.toString()); 
} 

boolean hasMoreTokens() { 
    return pos < expression.length; 
} 

public static void main(String[] args) { 
    String expression = "54+18+5"; 
    Tokenizer tokenizer = new Tokenizer(expression); 
    while (tokenizer.hasMoreTokens()) { 
     Lexeme nextToken = tokenizer.getNextToken(); 
     System.out.print("Type: " + nextToken.type + "\tLexeme: " + nextToken.token + "\n"); 
    } 
} 


}

來源

2014-12-06 user3513220

這裏這部分是它正在尋找一個數字，給出了一個非數字或非週期性質的錯誤。

if(Character.isDigit(expression[pos]) || expression[pos] == '.') { 
    token.append(expression[pos]); 
    type = Type.LITTER; 
} else { 
    System.out.println("Systax error at position: " + pos); 
}

字符串可以normallly不放任何東西，所以你只想消除if語句，做

default: 
    token.append(expression[pos]);

但是，如果你想限制你的字符串中的字符，然後修改，如果條件檢查你想要的角色。而不是：

if(Character.isDigit(expression[pos]) || expression[pos] == '.') {

將其更改爲只接受您認爲在字符串中有效的字符。例如

if (Character.isAlphabetic(expression[pos]) || expression[pos] == "-") {

您可能還需要一個新的標識，而不是

type = Type.LITTER;

來源

2014-12-06 13:15:21 Scooter

我努力，因爲你發佈你的答案，但沒有你能不能請張貼檢查所有字母和什麼是所有代碼無效在此先感謝 – user3513220 2014-12-06 14:02:15

什麼字符是字母 - 只是AZ，az？ – Scooter 2014-12-06 14:18:25

字符是字母a-z – user3513220 2014-12-06 14:55:19

我不知道你想怎麼處理「A12」或任何部分是字母和數字的一部分。此代碼將返回「A」爲「A12」

package lexical; 

public class Tokenizer { 

    int pos; 
    char[] expression; 

    Tokenizer(String expression) { 
     this.expression = expression.toCharArray(); 
     this.pos = 0; 
    } 

    enum Type { 

     OPERATOR, ALPHA, UNKNOWN, LITTER, ERROR 
    } 

    class Lexeme { 

     String type, token; 

     Lexeme(String type, String token) { 
      this.type = type; 
      this.token = token; 
     } 
    } 

    Lexeme getNextToken() { 
     StringBuilder token = new StringBuilder(); 
     boolean endOfToken = false; 
     Type type = Type.UNKNOWN; 
     // skip whitespace 
     while (expression[pos] == ' ' && hasMoreTokens()) { 
      pos++; 
     } 

     while (!endOfToken && hasMoreTokens()) { 

      switch (expression[pos]) { 
       case ' ': 
       { 
        endOfToken = true; 
        pos++; 
        break; 
       } 
       default: 
        if (Character.isAlphabetic(expression[pos])) {      
         token.append(expression[pos]); 
         type = Type.ALPHA;      
        } else { 
         System.out.println("Systax error at position: " + pos); 
        } 
        pos++; 
        break; 
      } 
     } 
     return new Lexeme(type.name().toLowerCase(), token.toString()); 
    } 

    boolean hasMoreTokens() { 
     return pos < expression.length; 
    } 

    public static void main(String[] args) { 
     expression = "Hello World"; 
     Tokenizer tokenizer = new Tokenizer(expression); 
     while (tokenizer.hasMoreTokens()) { 
      Lexeme nextToken = tokenizer.getNextToken(); 
      System.out.print("Type: " + nextToken.type + "\tLexeme: " + nextToken.token + "\n"); 
     }   
     expression = "123 ABC A12"; 
     tokenizer = new Tokenizer(expression); 
     while (tokenizer.hasMoreTokens()) { 
      Lexeme nextToken = tokenizer.getNextToken(); 
      System.out.print("Type: " + nextToken.type + "\tLexeme: " + nextToken.token + "\n"); 
     }   
    } 
}

輸出：

Type: alpha Lexeme: Hello 
Type: alpha Lexeme: World 
Systax error at position: 0 
Systax error at position: 1 
Systax error at position: 2 
Type: unknown Lexeme: 
Type: alpha Lexeme: ABC 
Systax error at position: 9 
Systax error at position: 10 
Type: alpha Lexeme: A

來源

2014-12-06 16:09:28 Scooter

詞法分析在Java中的字母

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