如何用stringtokenizer生成扫描器

Question

我在这段代码中遇到问题，我试图在编译器过程中为我的项目构建一个扫描器，扫描器从用户处获取任何输入并将其分离为令牌。将是：打印每个令牌和它的类型（如：号码，标识符，关键字，加号等），最后打印令牌的数量。

我试图多个输入端，并且每个时间输出是标识符，并且当我试图输入一个号码或关键字或+或 - 的输出是标识..

这是我的代码：

import java.util.Scanner; 
import java.util.StringTokenizer; 

public class MyScanner 
{ 
    public static void main(String[] args) 
    { 
     String reserved_Keywords[] = { "abstract", "assert", "boolean", 
       "break", "byte", "case", "catch", "char", "class", "const", 
       "continue", "default", "do", "double", "else", "extends", "false", 
       "final", "finally", "float", "for", "goto", "if", "implements", 
       "import", "instanceof", "int", "interface", "long", "native", 
       "new", "null", "package", "private", "protected", "public", 
       "return", "short", "static", "strictfp", "super", "switch", 
       "synchronized", "this", "throw", "throws", "transient", "true", 
       "try", "void", "volatile", "while" }; 
     Scanner sc = new Scanner(System.in); 
     System.out.println("Enter Your Text: "); 
     String str = sc.nextLine(); 
     StringTokenizer st = new StringTokenizer(str); 
     int numofTokens = st.countTokens(); 
     while(st.hasMoreElements()) 
     { 
      for (int i = 0; i < reserved_Keywords.length; i++) 
      { 
       if (st.equals(reserved_Keywords[i])) 
       { 
        System.out.print(st.nextElement() + "\t"); 
        System.out.println("Is Reserved Keyword"); 
       } 
      } 

      if (st.equals("+")) 
      { 
       System.out.print(st.nextElement() + "\t"); 
       System.out.println("Is Plus Sign"); 
      } 

      else if (st.equals("-")) 
      { 
       System.out.print(st.nextElement() + "\t"); 
       System.out.println("Is Minus Sign"); 
      } 

      else if (st.equals("*")) 
      { 
       System.out.print(st.nextElement() + "\t"); 
       System.out.println("Is Multiply Sign"); 
      } 

      else if(st.equals("/")) 
      { 
       System.out.print(st.nextElement() + "\t"); 
       System.out.println("Is Divide Sign"); 
      } 

      else if (st.equals("=")) 
      { 
       System.out.print(st.nextElement() + "\t"); 
       System.out.println("Is Assignment Operator"); 
      } 

      else 
      { 
       System.out.print(st.nextElement() + "\t"); 
       System.out.println("Is Identifier"); 
      } 
     } 
     sc.close(); 
     System.out.println("Number of Tokens = " + numofTokens); 
    } 
} 

Answer 1

你总是比较（调用等于（..）（与StringTokenizer的，而不是由StringTokenizer类返回的令牌。

提起这一点，添加的，而第一线环

String TOKEN = st.nextToken(); 

然后用st而不是TOKEN替换所有比较（调用equals（））。

（你应该课程名称不变量，大写字母，我这样做只是为了便于阅读）

那么你的代码如下：

StringTokenizer st = new StringTokenizer(str); 
    int numofTokens = st.countTokens(); 
    while(st.hasMoreElements()) 
    { 
     String TOKEN = st.nextToken(); 
     for (int i = 0; i < reserved_Keywords.length; i++) 
     { 
      if (TOKEN.equals(reserved_Keywords[i])) 
      { 
       System.out.print(st.nextElement() + "\t"); 
       System.out.println("Is Reserved Keyword"); 
      } 
     } 

...