001/* 
002    Licensed to the Apache Software Foundation (ASF) under one
003    or more contributor license agreements.  See the NOTICE file
004    distributed with this work for additional information
005    regarding copyright ownership.  The ASF licenses this file
006    to you under the Apache License, Version 2.0 (the
007    "License"); you may not use this file except in compliance
008    with the License.  You may obtain a copy of the License at
009
010       http://www.apache.org/licenses/LICENSE-2.0
011
012    Unless required by applicable law or agreed to in writing,
013    software distributed under the License is distributed on an
014    "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
015    KIND, either express or implied.  See the License for the
016    specific language governing permissions and limitations
017    under the License.  
018 */
019package org.apache.wiki.workflow;
020
021import java.io.Serializable;
022
023/**
024 * Represents a contextual artifact, which can be any serializable object, useful for making
025 * a Decision. Facts are key-value pairs, where the key is a String (message
026 * key) and the value is an arbitrary object. Generally, the supplied object's
027 * {@link #toString()} method should return a human-readable String. Facts are
028 * immutable objects.
029 * 
030 * @since 2.5
031 */
032public final class Fact implements Serializable
033{
034    private static final long serialVersionUID = -7459432935402796978L;
035
036    private final String m_key;
037
038    private final Serializable m_obj;
039
040    /**
041     * Constructs a new Fact with a supplied message key and value.
042     * 
043     * @param messageKey
044     *            the "name" of this fact, which should be an i18n message key
045     * @param value
046     *            the object to associate with the name
047     */
048    public Fact(final String messageKey, final Serializable value)
049    {
050        if ( messageKey == null || value == null )
051        {
052            throw new IllegalArgumentException( "Fact message key or value parameters must not be null." );
053        }
054        m_key = messageKey;
055        m_obj = value;
056    }
057
058    /**
059     * Returns this Fact's name, as represented an i18n message key.
060     * @return the message key
061     */
062    public String getMessageKey()
063    {
064        return m_key;
065    }
066
067    /**
068     * Returns this Fact's value.
069     * @return the value object
070     */
071    public Serializable getValue()
072    {
073        return m_obj;
074    }
075    
076    /**
077     * Two Facts are considered equal if their message keys and value objects are equal.
078     * @param obj the object to test
079     * @return <code>true</code> if logically equal, <code>false</code> if not
080     */
081    public boolean equals(final Object obj )
082    {
083        if ( !( obj instanceof Fact ) ) 
084        {
085            return false;
086        }
087        
088        final Fact f = (Fact)obj;
089        return m_key.equals( f.m_key) && m_obj.equals( f.m_obj );
090    }
091    
092    /**
093     * {@inheritDoc}
094     */
095    public int hashCode()
096    {
097        return m_key.hashCode() + 41 * m_obj.hashCode();
098    }
099
100    /**
101     * Returns a String representation of this Fact.
102     * @return the representation
103     */
104    public String toString()
105    {
106        return "[Fact:" + m_obj + "]";
107    }
108}