java编写词法分析器

/**
 * 此程序是通过将文件的字符读取到字符数组中去，然后遍历数组，将读取的字符进行
 * 分类并输出
 * @author
 *
 */
public class WordAnalyze {
    private String keyWord[] = {"break","include","begin","end","if","else","while","switch"};
    private char ch;
    //判断是否是关键字
    boolean isKey(String str)
    {
        for(int i = 0;i < keyWord.length;i++)
        {
            if(keyWord[i].equals(str))
                return true;
        }
        return false;
    }
    //判断是否是字母
    boolean isLetter(char letter)
    {
        if((letter >= ‘a‘ && letter <= ‘z‘)||(letter >= ‘A‘ && letter <= ‘Z‘))
            return true;
        else
            return false;
    }
    //判断是否是数字
    boolean isDigit(char digit)
    {
        if(digit >= ‘0‘ && digit <= ‘9‘)
            return true;
        else
            return false;
    }
    //词法分析
    void analyze(char[] chars)
    {
        String arr = "";
        for(int i = 0;i< chars.length;i++) {
            ch = chars[i];
            arr = "";
            if(ch == ‘ ‘||ch == ‘\t‘||ch == ‘\n‘||ch == ‘\r‘){}
            else if(isLetter(ch)){
                while(isLetter(ch)||isDigit(ch)){    
                    arr += ch;
                    ch = chars[++i];
                }
                //回退一个字符
                i--;
                if(isKey(arr)){
                    //关键字
                    System.out.println(arr+"\t4"+"\t关键字");
                }
                else{
                    //标识符
                    System.out.println(arr+"\t4"+"\t标识符");
                }
            }
            else if(isDigit(ch)||(ch == ‘.‘))
            {
                while(isDigit(ch)||(ch == ‘.‘&&isDigit(chars[++i])))
                {
                    if(ch == ‘.‘) i--;
                    arr = arr + ch;
                    ch = chars[++i];
                }
                //属于无符号常数
                System.out.println(arr+"\t5"+"\t常数");
            }
            else switch(ch){
                //运算符
                case ‘+‘:System.out.println(ch+"\t2"+"\t运算符");break;
                case ‘-‘:System.out.println(ch+"\t2"+"\t运算符");break;
                case ‘*‘:System.out.println(ch+"\t2"+"\t运算符");break;
                case ‘/‘:System.out.println(ch+"\t2"+"\t运算符");break;
                //分界符
                case ‘(‘:System.out.println(ch+"\t3"+"\t分界符");break;
                case ‘)‘:System.out.println(ch+"\t3"+"\t分界符");break;
                case ‘[‘:System.out.println(ch+"\t3"+"\t分界符");break;
                case ‘]‘:System.out.println(ch+"\t3"+"\t分界符");break;
                case ‘;‘:System.out.println(ch+"\t3"+"\t分界符");break;
                case ‘{‘:System.out.println(ch+"\t3"+"\t分界符");break;
                case ‘}‘:System.out.println(ch+"\t3"+"\t分界符");break;
                //运算符
                case ‘=‘:{
                            ch = chars[++i];
                            if(ch == ‘=‘)System.out.println("=="+"\t2"+"\t运算符");
                            else {
                                System.out.println("="+"\t2"+"\t运算符");
                                i--;
                            }
                         }break;
                case ‘:‘:{
                            ch = chars[++i];
                            if(ch == ‘=‘)System.out.println(":="+"\t2"+"\t运算符");
                            else {
                                System.out.println(":"+"\t2"+"\t运算符");
                                i--;
                            }
                         }break;
                case ‘>‘:{
                            ch = chars[++i];
                            if(ch == ‘=‘)System.out.println(">="+"\t2"+"\t运算符");
                            else {
                                System.out.println(">"+"\t2"+"\t运算符");
                                i--;
                            }
                         }break;
                case ‘<‘:{
                            ch = chars[++i];
                            if(ch == ‘=‘)System.out.println("<="+"\t2"+"\t运算符");
                            else {
                                System.out.println("<"+"\t2"+"\t运算符");
                                i--;
                            }
                         }break;
                //无识别
                default: System.out.println(ch+"\t6"+"\t无识别符");
            }
        }
    }
public static void main(String[] args) throws Exception {
    File file = new File("E:\\data.txt");//定义一个file对象，用来初始化FileReader
    FileReader reader = new FileReader(file);//定义一个fileReader对象，用来初始化BufferedReader
    int length = (int) file.length();
    //这里定义字符数组的时候需要多定义一个,因为词法分析器会遇到超前读取一个字符的时候，如果是最后一个
    //字符被读取，如果在读取下一个字符就会出现越界的异常
    char buf[] = new char[length+1];
    reader.read(buf);
    reader.close();
    new WordAnalyze().analyze(buf);
    
}
}