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.implementations;
033
034import org.graphstream.graph.Edge;
035import org.graphstream.graph.Node;
036import org.graphstream.stream.SourceBase.ElementType;
037
038/**
039 * <p>
040 * This class provides a basic implementation of {@code Edge} interface, to
041 * minimize the effort required to implement this interface.
042 * </p>
043 * 
044 * <p>
045 * Although this class is abstract it implements all the methods of
046 * {@link org.graphstream.graph.Edge} and
047 * {@link org.graphstream.graph.implementations.AbstractElement}. It has a low
048 * memory overhead (3 references and a boolean as fields). All {@code Edge}
049 * methods are executed in O(1) time.
050 * </p>
051 */
052public class AbstractEdge extends AbstractElement implements Edge {
053
054        // *** Fields ***
055
056        /**
057         * The source node
058         */
059        protected AbstractNode source;
060
061        /**
062         * The target node
063         */
064        protected AbstractNode target;
065
066        /**
067         * Is this edge directed ?
068         */
069        protected boolean directed;
070
071        /**
072         * The graph to which this edge belongs
073         */
074        protected AbstractGraph graph;
075
076        // *** Constructors ***
077
078        /**
079         * Constructs a new edge. This constructor copies the parameters into the
080         * corresponding fields.
081         * 
082         * @param id
083         *            Unique identifier of this edge.
084         * @param source
085         *            Source node.
086         * @param target
087         *            Target node.
088         * @param directed
089         *            Indicates if the edge is directed.
090         */
091        protected AbstractEdge(String id, AbstractNode source, AbstractNode target,
092                        boolean directed) {
093                super(id);
094                assert source != null && target != null : "An edge cannot have null endpoints";
095                this.source = source;
096                this.target = target;
097                this.directed = directed;
098                this.graph = (AbstractGraph) source.getGraph();
099        }
100
101        // *** Inherited from AbstractElement ***
102
103        @Override
104        protected void attributeChanged(AttributeChangeEvent event,
105                        String attribute, Object oldValue, Object newValue) {
106                graph.listeners.sendAttributeChangedEvent(id, ElementType.EDGE,
107                                attribute, event, oldValue, newValue);
108        }
109
110        /**
111         * This implementation calls the corresponding method of the parent graph
112         * 
113         * @see org.graphstream.graph.implementations.AbstractElement#nullAttributesAreErrors()
114         */
115        @Override
116        protected boolean nullAttributesAreErrors() {
117                return graph.nullAttributesAreErrors();
118        }
119
120        @Override
121        public String toString() {
122                return String.format("%s[%s-%s%s]", getId(), source, directed ? ">"
123                                : "-", target);
124        }
125
126        // *** Inherited from Edge ***
127
128        @SuppressWarnings("unchecked")
129        public <T extends Node> T getNode0() {
130                return (T) source;
131        }
132
133        @SuppressWarnings("unchecked")
134        public <T extends Node> T getNode1() {
135                return (T) target;
136        }
137
138        @SuppressWarnings("unchecked")
139        public <T extends Node> T getOpposite(Node node) {
140                if (node == source)
141                        return (T) target;
142                if (node == target)
143                        return (T) source;
144                return null;
145        }
146
147        @SuppressWarnings("unchecked")
148        public <T extends Node> T getSourceNode() {
149                return (T) source;
150        }
151
152        @SuppressWarnings("unchecked")
153        public <T extends Node> T getTargetNode() {
154                return (T) target;
155        }
156
157        public boolean isDirected() {
158                return directed;
159        }
160
161        public boolean isLoop() {
162                return source == target;
163        }
164}