词法分析器，用java实现，采用的核心算法是通过函数readch()把下一个输入字符读到变量peek中，函数scan在略过所有空白字符后，首先试图识别像<=这样的复合词法单元和整数数字，如果不成功，它就试图读入一个字符。-Lexical analyzer, with java implementation, the core algorithm used by the function readch () to read the next input character variable peek, the function scan skip all white space characters in after the first attempt to identify as < = such a complex lexical unit and integer numbers, if unsuccessful, it tried to read a character.