001    package org.apache.commons.graph;
002    
003    /*
004     * Licensed to the Apache Software Foundation (ASF) under one
005     * or more contributor license agreements.  See the NOTICE file
006     * distributed with this work for additional information
007     * regarding copyright ownership.  The ASF licenses this file
008     * to you under the Apache License, Version 2.0 (the
009     * "License"); you may not use this file except in compliance
010     * with the License.  You may obtain a copy of the License at
011     *
012     *   http://www.apache.org/licenses/LICENSE-2.0
013     *
014     * Unless required by applicable law or agreed to in writing,
015     * software distributed under the License is distributed on an
016     * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
017     * KIND, either express or implied.  See the License for the
018     * specific language governing permissions and limitations
019     * under the License.
020     */
021    
022    /**
023     * An {@code Edge} is the link that connect a pair of {@link Vertex}.
024     *
025     * A {@link Graph} in which {@link Edge}s have no orientation, {@link Vertex} members are not ordered pairs.
026     *
027     * In a {@link DirectedGraph}, {@link Edge}s have orientation, so relation expressed by the {@link Edge} has to be
028     * intended from {@link #getHead()} to {@link #getTail()}.
029     *
030     * @param <V> the Graph vertices type
031     */
032    public interface Edge<V extends Vertex>
033    {
034    
035        /**
036         * Return the head of this edge.
037         *
038         * @return the head of this edge.
039         */
040        V getHead();
041    
042        /**
043         * Return the tail of this edge.
044         *
045         * @return the tail of this edge.
046         */
047        V getTail();
048    
049    }