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    import java.util.Set;
023    
024    /**
025     * A {@code DirectedGraph} or <i>digraph</i> is an ordered pair {@code D = ( V, E )} with
026     * <ul>
027     * {@code V} a set whose elements are called vertices or nodes, and
028     * {@code E} a set of ordered pairs of vertices, called arcs, directed edges, or arrows.
029     * </ul>
030     *
031     * @param <V> the Graph vertices type
032     * @param <E> the Graph edges type
033     */
034    public interface DirectedGraph<V extends Vertex, E extends Edge<V>>
035        extends Graph<V, E>
036    {
037    
038        /**
039         * Returns the set of {@link Edge}s which are inbound to the {@link Vertex}.
040         *
041         * @param v the {@link Vertex} which inbound {@link Edge}s have to be returned
042         * @return the set of {@link Edge}s which are inbound to the {@link Vertex}.
043         */
044        Set<E> getInbound( V v );
045    
046        /**
047         * Returns the set of {@link Edge}s which lead away from the {@link Vertex}.
048         *
049         * @param v the {@link Vertex} which outbound {@link Edge}s have to be returned
050         * @return the set of {@link Edge}s which lead away from the {@link Vertex}.
051         */
052        Set<E> getOutbound( V v );
053    
054    }