package lexer;
public class Token {
public final int tag;
public Token(int t) {
tag = t;
}
public String toString() {
return "" + (char) tag;
}
}
package lexer;
public class Tag {
public final static int AND = 256, BASIC = 257, BREAK = 258, DO = 259,
ELSE = 260, EQ = 261, FALSE = 262, GE = 263, ID = 264, IF = 265,
INDEX = 266, LE = 267, MINUS = 268, NE = 269, NUM = 270, OR = 271,
REAL = 272, TEMP = 273, TRUE = 274, WHILE = 275;
}
package lexer;
public class Real extends Token {
public final float value;
public Real(float v) {
super(Tag.REAL);
value = v;
}
public String toString() {
return "" + value;
}
}
package lexer;
public class Num extends Token {
public final int value;
public Num(int v) {
super(Tag.NUM);
value = v;
}
public String toString() {
return "" + value;
}
}
package lexer;
public class Word extends Token {
public String lexeme = "";
public Word(String s, int tag) {
super(tag);
lexeme = s;
}
public String toString() {
return lexeme;
}
public static final Word and = new Word("&&", Tag.AND), or = new Word("||",
Tag.OR), eq = new Word("==", Tag.EQ), ne = new Word("!=", Tag.NE),
le = new Word("<=", Tag.LE), ge = new Word(">=", Tag.GE),
minus = new Word("minus", Tag.MINUS), True = new Word("true",
Tag.TRUE), False = new Word("false", Tag.FALSE),
temp = new Word("t", Tag.TEMP);
}
package lexer;
import java.io.IOException;
import java.util.Hashtable;
public class Lexer {
public static int line = 1;
char peek = ' ';
Hashtable words = new Hashtable();
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);
}
public void readch() throws IOException {
peek = (char) System.in.read();
}
boolean readch(char c) throws IOException {
readch();
if (peek != c) {
return false;
}
peek = ' ';
return true;
}
public Token scan() throws IOException {
for (;; readch()) {
if (peek == ' ' || peek == '\t')
continue;
else if (peek == '\n') {
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;
}
public void out() {
System.out.println(words.size());
}
public char getPeek() {
return peek;
}
public void setPeek(char peek) {
this.peek = peek;
}
}
package main;
import java.io.IOException;
import java.util.Hashtable;
import lexer.Lexer;
import lexer.Token;
public class Main {
public static void main(String[] args) throws IOException {
Lexer lexer = new Lexer();
char c;
do {
Token token=lexer.scan();
switch (token.tag) {
case 270:
case 272:
System.out.println("(NUM , "+token.toString()+")");
break;
case 264:
System.out.println("(ID , "+token.toString()+")");
break;
case 256:
case 257:
case 258:
case 259:
case 260:
case 265:
case 274:
case 275:
System.out.println("(KEY , "+token.toString()+")");
break;
case 13:
break;
default:
System.out.println("(SYM , "+token.toString()+")");
break;
}
} while (lexer.getPeek()!='\n');
}
}
怎么把上面从控制台输入的代码改成读取txt文件输入
