scope.java

国外的一套开源CRM

package org.ofbiz.rules.engine;


import java.util.*;
import org.ofbiz.rules.utensil.*;


/**
 * <p><b>Title:</b> Scope
 * <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>A scope is a repository for variables. A dynamic rule has
 * a scope, which means that variables with the same name
 * are the same variable. Consider a rule that describes
 * big cities:
 *
 * <blockquote><pre>
 *     bigCity(Name) :- city(Name, Pop), >(Pop, 1000000);
 * </pre></blockquote>
 *
 * This example follows the Prolog convention of using
 * capitalized words for variables. The variables <code>Name
 * </code> and <code>Pop</code> have scope throughout the rule.
 * <p>
 * The <code>bigCity</code> rule proves itself by finding
 * a city and checking its population. When the <code>city
 * </code> structure binds with a city fact in a program, its
 * variables take on the values of the fact. For example,
 * <code>city</code> might bind with the fact <code>
 * city(bigappolis, 8733352) </code>. Then <code>Name</code>
 * and <code>Pop</code> will bind to the values "bigappolis"
 * and 8733352.
 * <p>
 * When the comparison proves itself, it will compare <code>
 * Pop</code> to 1000000. This is the same variable as <code>
 * Pop</code> in the <code>city</code> structure of the rule.
 * With this successful comparison, the rule completes a
 * successful proof, with <code>Name</code> bound to
 * "bigappolis".
 *
 * @author Steven J. Metsker
 * @version 1.0
 */
public class Scope implements PubliclyCloneable {
    Hashtable dictionary = new Hashtable();

    /**
     * Create an empty scope.
     */
    public Scope() {}

    /**
     * Create a scope that uses the variables in the supplied
     * terms.
     *
     * @param Term[] the terms to seed this scope with
     */
    public Scope(Term terms[]) {
        for (int i = 0; i < terms.length; i++) {
            Unification u = terms[i].variables();
            Enumeration e = u.elements();

            while (e.hasMoreElements()) {
                Variable v = (Variable) e.nextElement();

                dictionary.put(v.name, v);
            }
        }
    }

    /**
     * Remove all variables from this scope.
     */
    public void clear() {
        dictionary.clear();
    }

    /**
     * Return a copy of this object.
     *
     * @return a copy of this object
     */
    public Object clone() {
        try {
            Scope clone = (Scope) super.clone();

            clone.dictionary = (Hashtable) dictionary.clone();
            return clone;
        } catch (CloneNotSupportedException e) {
            // this shouldn't happen, since we are Cloneable
            throw new InternalError();
        }
    }

    /**
     * Returns true if a variable of the given name appears
     * in this scope.
     *
     * @param String the variable name
     *
     * @return true, if a variable of the given name appears
     *         in this scope.
     */
    public boolean isDefined(String name) {
        return dictionary.containsKey(name);
    }

    /**
     * Returns a variable of the given name from this scope.
     *
     * If the so-named variable is not already in this scope,
     * the scope will create it and add the variable to itself.
     *
     * @param String the variable name
     *
     * @return a variable of the given name from this scope
     */
    public Variable lookup(String name) {
        Variable v = (Variable) dictionary.get(name);

        if (v == null) {
            v = new Variable(name);
            dictionary.put(v.name, v);
        }
        return v;
    }
}