alternation.java

国外的一套开源CRM

package org.ofbiz.rules.parse;


import java.util.*;


/**
 * <p><b>Title:</b> Alternation
 * <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>
 * <p>An <code>Alternation</code> object is a collection of
 * parsers, any one of which can successfully match against
 * an assembly.
 *
 * @author Steven J. Metsker
 * @version 1.0
 */
public class Alternation extends CollectionParser {

    /**
     * Constructs a nameless alternation.
     */
    public Alternation() {}

    /**
     * Constructs an alternation with the given name.
     *
     * @param    name    a name to be known by
     */
    public Alternation(String name) {
        super(name);
    }

    /**
     * Accept a "visitor" and a collection of previously visited
     * parsers.
     *
     * @param   pv   the visitor to accept
     *
     * @param   visited   a collection of previously visited parsers
     */
    public void accept(ParserVisitor pv, List visited) {
        pv.visitAlternation(this, visited);
    }

    /**
     * Given a set of assemblies, this method matches this
     * alternation against all of them, and returns a new set
     * of the assemblies that result from the matches.
     *
     * @return   a List of assemblies that result from
     *           matching against a beginning set of assemblies
     *
     * @param   in   a vector of assemblies to match against
     *
     */
    public List match(List in) {
        List out = new ArrayList();
        Enumeration e = Collections.enumeration(subparsers);

        while (e.hasMoreElements()) {
            Parser p = (Parser) e.nextElement();

            add(out, p.matchAndAssemble(in));
        }
        return out;
    }

    /**
     * Create a random collection of elements that correspond to
     * this alternation.
     */
    protected List randomExpansion(int maxDepth, int depth) {
        if (depth >= maxDepth) {
            return randomSettle(maxDepth, depth);
        }
        double n = (double) subparsers.size();
        int i = (int) (n * Math.random());
        Parser j = (Parser) subparsers.get(i);

        return j.randomExpansion(maxDepth, depth++);
    }

    /**
     * This method is similar to randomExpansion, but it will
     * pick a terminal if one is available.
     */
    protected List randomSettle(int maxDepth, int depth) {

        // which alternatives are terminals?

        List terms = new ArrayList();
        Enumeration e = Collections.enumeration(subparsers);

        while (e.hasMoreElements()) {
            Parser j = (Parser) e.nextElement();

            if (j instanceof Terminal) {
                terms.add(j);
            }
        }

        // pick one of the terminals or, if there are no
        // terminals, pick any subparser

        List which = terms;

        if (terms.isEmpty()) {
            which = subparsers;
        }

        double n = (double) which.size();
        int i = (int) (n * Math.random());
        Parser p = (Parser) which.get(i);

        return p.randomExpansion(maxDepth, depth++);
    }

    /**
     * Returns the string to show between the parsers this
     * parser is an alternation of.
     */
    protected String toStringSeparator() {
        return "|";
    }
}