词法分析器java版(java词法分析器)

无论是词法分析，还是语法分析，给我的第一感觉就是逻辑要严谨。由于项目有自己一套完整的语言和语法，设计好其对应的词法分析器和语法分析器显得尤为重要。

这里给您提供一个免费的java词法分析器下载

java词法分析器实现原理步骤

先写其正则式，然后NFA，然后DFA，然后对其进行优化，最后准备工作做好了，就可以开始写代码了。

    下面对其里面的主要函数进行讲解：
enum Token_Type {
     keyword =1,              //关键字
     Identifier,            //标识符
     operatorr,             //运算符
     operatorrd,             //单运算符
     constant,              //常量
     escape,                //转义符
     separator,              //界限符
     notype,                  //没有类型
     zhushi                   //注释类型
};

对其单词的类型定义成枚举。

typedef struct Token {
     Token_Type type; //其类型
     char *lexeme ;    //字符串
     int  value;       //属性值
}Token;

//返回单词的结构。

void InitScanner(char *ch){
     fp1 = fopen(ch,"r+");
     LineNo = 1;
}//初始化分析器。
void CloseScanner(){
     fclose(fp1);
}//关闭分析器
void EmptyTokenString(){
     memset(TokenBuffer,0,100);
}//清空缓冲区
static void AddCharTokenString(char Char)
{
    int TokenLenth=strlen(TokenBuffer);
    if(TokenLenth+1==sizeof(TokenBuffer)) return;
    TokenBuffer[TokenLenth]=Char;
    TokenBuffer[TokenLenth+1]='\0';
} //将一个字符添加到缓冲区
static char GetChar(){
     char Char;
     Char = fgetc(fp1);
     return Char;
}//从文件中读取一个字符
static void BackChar(char Char) {
     if(Char!=EOF){
         ungetc(Char,fp1);
     }
}//将其字符后退一个。

static Token JudgeKeyToken(char *IDstring)；//这个函数实现对关键字进行判断

下面是源代码：

/************************************************************************
*                CopyRight@ice-snow studio                              *
*               email:bingxuefenggu@126.com                             *
*               qq: 405116890                                           *
************************************************************************/
//只考虑到整形常量
//实型没考虑到
//需要解决转义符如何描述的问题
#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<ctype.h>
#define TOKEN_LEN 100

enum Token_Type {
     keyword =1,              //关键字
     Identifier,            //标识符
     operatorr,             //运算符
     operatorrd,             //单运算符
     constant,              //常量
     escape,                //转义符
     separator,              //界限符
     notype,                  //没有类型
     zhushi                   //注释类型
};
typedef struct Token {
     Token_Type type; //其类型
     char *lexeme ;    //字符串
     int  value;       //属性值
}Token;
static Token Token_Tap[] = {
       {keyword,"abstract",0x103},
       {keyword,"boolean",0x103},
       {keyword,"break", 0x103},
       {keyword,"byte" ,0x103},
       {keyword,"case",0x103},
       {keyword,"catch",0x103},
       {keyword,"char", 0x103},
       {keyword, "class",0x103},
       {keyword,"const" ,0x103},
       {keyword,"continue" ,0x103},
       {keyword,"default" , 0x103},
       {keyword,"do",0x103},
       {keyword,"double",0x103},
       {keyword,"else",0x103},
       {keyword,"extends",0x103},
       {keyword,"false",0x103},
       {keyword,"final",0x103},
       {keyword,"finally",0x103},
       {keyword,"float",0x103},
       {keyword,"for",0x103},
       {keyword,"goto",0x103},
       {keyword,"if",0x103},
       {keyword,"implements",0x103},
       {keyword,"import",0x103},
       {keyword,"instanceof",0x103},
       {keyword,"int",0x103},
       {keyword,"interface",0x103},
       {keyword,"long",0x103},
       {keyword,"native",0x103},
       {keyword,"new",0x103},
       {keyword,"null",0x103},
       {keyword,"package",0x103},
       {keyword,"private",0x103},
       {keyword,"protected",0x103},
       {keyword,"public",0x103},
       {keyword,"return",0x103},
       {keyword,"short",0x103},
       {keyword,"static",0x103},
       {keyword,"super",0x103},
       {keyword,"switch",0x103},
       {keyword,"synchronized",0x103},
       {keyword,"this",0x103},
       {keyword,"throw",0x103},
       {keyword,"throws",0x103},
       {keyword,"transient",0x103},
       {keyword,"true",0x103},
       {keyword,"try", 0x103},
       {keyword,"void",0x103},
       {keyword,"volatile",0x103},
       {keyword,"while",0x103},
       {constant,"true",0x105},
       {constant,"false",0x105}
     //以上是所有的关键字
};
FILE *fp1;// 要读文件的描述符
int LineNo;//单词所在的行数
static char TokenBuffer[TOKEN_LEN];//单词符号的缓存区
void InitScanner(char *ch){
     fp1 = fopen(ch,"r+");
     LineNo = 1;
}
void CloseScanner(){
     fclose(fp1);
}
void EmptyTokenString(){
     memset(TokenBuffer,0,100);
}
static void AddCharTokenString(char Char)
{
    int TokenLenth=strlen(TokenBuffer);
    if(TokenLenth+1==sizeof(TokenBuffer)) return;
    TokenBuffer[TokenLenth]=Char;
    TokenBuffer[TokenLenth+1]='\0';
}
static char GetChar(){
     char Char;
     Char = fgetc(fp1);
     return Char;
}
static void BackChar(char Char) {
     if(Char!=EOF){
         ungetc(Char,fp1);
     }
}
static Token JudgeKeyToken(char *IDstring){
     int loop;
     Token token;
     for(loop=0;loop<51;loop++){
         if(strcmp(Token_Tap[loop].lexeme,IDstring)==0)
         return Token_Tap[loop];
     }
     token.type = Identifier;
     //strcpy(token.lexeme,IDstring);//youwenti.
     token.lexeme = IDstring;
     token.value = 0x104;
     return token;
}