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158 lines (131 loc) · 4.35 KB
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// Scan lexical tokens in input strings.
package com.expr;
import java.util.Vector;
class Scanner {
private String s;
private String operatorChars;
Vector<Token> tokens = new Vector<>();
int index = -1;
public Scanner(String string, String operatorChars) {
this.s = string;
this.operatorChars = operatorChars;
int i = 0;
do {
i = scanToken(i);
} while (i < s.length());
}
public String getInput() {
return s;
}
// The tokens may have been diddled, so this can be different from
// getInput().
public String toString() {
StringBuffer sb = new StringBuffer();
int whitespace = 0;
for (int i = 0; i < tokens.size(); ++i) {
Token t = tokens.elementAt(i);
int spaces = (whitespace != 0 ? whitespace : t.leadingWhitespace);
if (i == 0)
spaces = 0;
else if (spaces == 0 && !joinable(tokens.elementAt(i - 1), t))
spaces = 1;
for (int j = spaces; 0 < j; --j)
sb.append(" ");
sb.append(t.sval);
whitespace = t.trailingWhitespace;
}
return sb.toString();
}
private boolean joinable(Token s, Token t) {
return !(isAlphanumeric(s) && isAlphanumeric(t));
}
private boolean isAlphanumeric(Token t) {
return t.ttype == Token.TT_WORD || t.ttype == Token.TT_NUMBER;
}
public boolean isEmpty() {
return tokens.size() == 0;
}
public boolean atStart() {
return index <= 0;
}
public boolean atEnd() {
return tokens.size() <= index;
}
public Token nextToken() {
++index;
return getCurrentToken();
}
public Token getCurrentToken() {
if (atEnd())
return new Token(Token.TT_EOF, 0, s, s.length(), s.length());
return (Token) tokens.elementAt(index);
}
private int scanToken(int i) {
while (i < s.length() && Character.isWhitespace(s.charAt(i)))
++i;
if (i == s.length()) {
return i;
} else if (0 <= operatorChars.indexOf(s.charAt(i))) {
if (i + 1 < s.length()) {
String pair = s.substring(i, i + 2);
int ttype = 0;
switch (pair) {
case "<=":
ttype = Token.TT_LE;
break;
case ">=":
ttype = Token.TT_GE;
break;
case "<>":
ttype = Token.TT_NE;
break;
}
if (0 != ttype) {
tokens.addElement(new Token(ttype, 0, s, i, i + 2));
return i + 2;
}
}
tokens.addElement(new Token(s.charAt(i), 0, s, i, i + 1));
return i + 1;
} else if (Character.isLetter(s.charAt(i))) {
return scanSymbol(i);
} else if (Character.isDigit(s.charAt(i)) || '.' == s.charAt(i)) {
return scanNumber(i);
} else {
tokens.addElement(makeErrorToken(i, i + 1));
return i + 1;
}
}
private int scanSymbol(int i) {
int from = i;
while (i < s.length()
&& (Character.isLetter(s.charAt(i))
|| Character.isDigit(s.charAt(i))))
++i;
tokens.addElement(new Token(Token.TT_WORD, 0, s, from, i));
return i;
}
private int scanNumber(int i) {
int from = i;
// We include letters in our purview because otherwise we'd
// accept a word following with no intervening space.
for (; i < s.length(); ++i)
if ('.' != s.charAt(i)
&& !Character.isDigit(s.charAt(i))
&& !Character.isLetter(s.charAt(i)))
break;
String text = s.substring(from, i);
double nval;
try {
nval = Double.valueOf(text);
} catch (NumberFormatException nfe) {
tokens.addElement(makeErrorToken(from, i));
return i;
}
tokens.addElement(new Token(Token.TT_NUMBER, nval, s, from, i));
return i;
}
private Token makeErrorToken(int from, int i) {
return new Token(Token.TT_ERROR, 0, s, from, i);
}
}