symbolstate.java

国外的一套开源CRM

package org.ofbiz.rules.parse.tokens;


import java.io.*;


/**
 * <p><b>Title:</b> Symbol State
 * <p><b>Description:</b> None
 * <p>Copyright (c) 1999 Steven J. Metsker.
 * <p>Copyright (c) 2001 The Open For Business Project - www.ofbiz.org
 *
 * <p>Permission is hereby granted, free of charge, to any person obtaining a
 *  copy of this software and associated documentation files (the "Software"),
 *  to deal in the Software without restriction, including without limitation
 *  the rights to use, copy, modify, merge, publish, distribute, sublicense,
 *  and/or sell copies of the Software, and to permit persons to whom the
 *  Software is furnished to do so, subject to the following conditions:
 *
 * <p>The above copyright notice and this permission notice shall be included
 *  in all copies or substantial portions of the Software.
 *
 * <p>THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
 *  OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
 *  MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
 *  IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
 *  CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT
 *  OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR
 *  THE USE OR OTHER DEALINGS IN THE SOFTWARE.
 *
 * <br>
 * The idea of a symbol is a character that stands on its
 * own, such as an ampersand or a parenthesis. For example,
 * when tokenizing the expression <code>(isReady)&
 * (isWilling) </code>, a typical tokenizer would return 7
 * tokens, including one for each parenthesis and one for
 * the ampersand. Thus a series of symbols such as
 * <code>)&( </code> becomes three tokens, while a series
 * of letters such as <code>isReady</code> becomes a single
 * word token.
 * <p>
 * Multi-character symbols are an exception to the rule
 * that a symbol is a standalone character.  For example, a
 * tokenizer may want less-than-or-equals to tokenize as a
 * single token. This class provides a method for
 * establishing which multi-character symbols an object of
 * this class should treat as single symbols. This allows,
 * for example, <code>"cat <= dog"</code> to tokenize as
 * three tokens, rather than splitting the less-than and
 * equals symbols into separate tokens.
 * <p>
 * By default, this state recognizes the following multi-
 * character symbols: <code>!=, :-, <=, >=</code>
 *
 * @author Steven J. Metsker
 * @version 1.0
 */
public class SymbolState extends TokenizerState {
    SymbolRootNode symbols = new SymbolRootNode();

    /**
     * Constructs a symbol state with a default idea of what
     * multi-character symbols to accept (as described in the
     * class comment).
     *
     * @return   a state for recognizing a symbol
     */
    public SymbolState() {
        add("!=");
        add(":-");
        add("<=");
        add(">=");
    }

    /**
     * Add a multi-character symbol.
     *
     * @param   String   the symbol to add, such as "=:="
     */
    public void add(String s) {
        symbols.add(s);
    }

    /**
     * Return a symbol token from a reader.
     *
     * @return a symbol token from a reader
     */
    public Token nextToken(
        PushbackReader r, int first, Tokenizer t)
        throws IOException {

        String s = symbols.nextSymbol(r, first);

        return new Token(Token.TT_SYMBOL, s, 0);
    }
}