001/*
002 * Copyright 2006 - 2013
003 *     Stefan Balev     <stefan.balev@graphstream-project.org>
004 *     Julien Baudry    <julien.baudry@graphstream-project.org>
005 *     Antoine Dutot    <antoine.dutot@graphstream-project.org>
006 *     Yoann Pigné      <yoann.pigne@graphstream-project.org>
007 *     Guilhelm Savin   <guilhelm.savin@graphstream-project.org>
008 * 
009 * This file is part of GraphStream <http://graphstream-project.org>.
010 * 
011 * GraphStream is a library whose purpose is to handle static or dynamic
012 * graph, create them from scratch, file or any source and display them.
013 * 
014 * This program is free software distributed under the terms of two licenses, the
015 * CeCILL-C license that fits European law, and the GNU Lesser General Public
016 * License. You can  use, modify and/ or redistribute the software under the terms
017 * of the CeCILL-C license as circulated by CEA, CNRS and INRIA at the following
018 * URL <http://www.cecill.info> or under the terms of the GNU LGPL as published by
019 * the Free Software Foundation, either version 3 of the License, or (at your
020 * option) any later version.
021 * 
022 * This program is distributed in the hope that it will be useful, but WITHOUT ANY
023 * WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A
024 * PARTICULAR PURPOSE.  See the GNU Lesser General Public License for more details.
025 * 
026 * You should have received a copy of the GNU Lesser General Public License
027 * along with this program.  If not, see <http://www.gnu.org/licenses/>.
028 * 
029 * The fact that you are presently reading this means that you have had
030 * knowledge of the CeCILL-C and LGPL licenses and that you accept their terms.
031 */
032package org.graphstream.graph;
033
034import java.util.HashMap;
035
036/**
037 * Definition of some compound value that can be used as attribute and can be
038 * transformed to a hash map.
039 * 
040 * <p>
041 * The purpose of this class is to allow to specify how some values are stored
042 * in the graph and can be exported to files (or others) when the graph is
043 * output. Most graph writers can only handle basic types for attributes (when
044 * they are able to store attributes in files). This interface may allow to
045 * store more complex attributes, made of several elements. The DGS writer is
046 * able to understand these kinds of attributes and store them in files.
047 * </p>
048 * 
049 * <p>
050 * The compound attribute is made of fields. Each fields has a name and a value.
051 * For these fields to be exported successfully, they must be transformable to a
052 * hash map where each element is indexed by its name (a String).
053 * </p>
054 * 
055 * <p>
056 * For the values to be exported successfully, they must either be basic types,
057 * or be themselves instances of CompountAttribute.
058 * </p>
059 */
060public interface CompoundAttribute {
061        /**
062         * Transforms this object to a hash map where each field is stored as a pair
063         * (key,value) where the key is the field name. As we cannot enforce the
064         * types of the key and value, the key are considered strings (or
065         * Object.toString()). The value is an arbitrary object.
066         * 
067         * @return The conversion of this attribute to a hash.
068         */
069        HashMap<?, ?> toHashMap();
070
071        /**
072         * The usual key used to store this attribute inside a graph element.
073         * 
074         * @return The attribute usual name.
075         */
076        String getKey();
077}