lexer.java

用java实现的编译器. 包括语法分析

package lexer;
import java.io.*;
import java.util.*;
import symbols.*;

public class Lexer {
	public static int line = 1;
	char peek = ' ';
	HashMap words = new HashMap();
	@SuppressWarnings("unchecked")
		void reserve(Word w) { words.put(w.lexeme, w);}
	public Lexer() {
		reserve(new Word("if", Tag.IF));
		reserve(new Word("else", Tag.ELSE));
		reserve(new Word("while", Tag.WHILE));
		reserve(new Word("do", Tag.DO));
		reserve(new Word("break", Tag.BREAK));
		reserve(Word.True);
		reserve(Word.False);
		reserve(Type.Int);
		reserve(Type.Char);
		reserve(Type.Bool);
		reserve(Type.Float);
	}

	void readch() throws IOException { 
		peek = (char)System.in.read();
	}
	boolean readch(char c) throws IOException {
		readch();
		if(peek != c) return false;
		peek = ' ';
		return true;
	}
	@SuppressWarnings("unchecked")
		public Token scan() throws IOException {
			for(;;readch()) {
				if(peek == ' ' || peek == '\t') continue;
				else if(peek == '\n') line = line +1;
				else break;
			}
			switch(peek) {
				case '&':
					if(readch('&')) return Word.and;
					else return new Token('&');
				case '|':
					if(readch('|')) return Word.or;
					else return new Token('|');
				case '=':
					if(readch('=')) return Word.eq;
					else return new Token('=');
				case '!':
					if(readch('=')) return Word.ne;
					else return new Token('!');
				case '<':
					if(readch('=')) return Word.le;
					else return new Token('<');
				case '>':
					if(readch('=')) return Word.ge;
					else return new Token('>');

			}
			if(Character.isDigit(peek)) {
				int v = 0;
				do {
					v = 10*v + Character.digit(peek, 10);
					readch();

				}while(Character.isDigit(peek));
				if(peek != '.') return new Num(v);
				float x = v;
				float d = 10;
				for(;;){
					readch();
					if(!Character.isDigit(peek)) break;
					x = x + Character.digit(peek, 10) / d;
					d = d*10;
				}
				return new Real(x);
			}
			if(Character.isLetter(peek)) {
				StringBuffer b = new StringBuffer();
				do {
					b.append(peek);
					readch();

				}while(Character.isLetterOrDigit(peek));
				String s = b.toString();
				Word w = (Word)words.get(s);
				if(w != null) return w;
				w = new Word(s, Tag.ID);
				words.put(s, w);
				return w;
			}
			Token tok = new Token(peek);
			peek =  ' ';
			return  tok; 
		}
}