code: /*
   * Computoser is a music-composition algorithm and a website to present the results
   * Copyright (C) 2012-2014  Bozhidar Bozhanov
   *
   * Computoser is free software: you can redistribute it and/or modify
   * it under the terms of the GNU Affero General Public License as
   * published by the Free Software Foundation, either version 3 of the
   * License, or (at your option) any later version.
   *
   * Computoser is distributed in the hope that it will be useful,
   * but WITHOUT ANY WARRANTY; without even the implied warranty of
   * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
   * GNU Affero General Public License for more details.
   *
   * You should have received a copy of the GNU Affero General Public License
   * along with Computoser.  If not, see <http://www.gnu.org/licenses/>.
   */
  
  package com.music.util;
  
  import java.util.HashSet;
  import java.util.Set;
  
  public class Graph<T> {
      private Set<Node<T>> nodes = new HashSet<Node<T>>();
      public void addNode(Node<T> node) {
          nodes.add(node);
      }
  
      public static class Node<T> {
          public final T value;
          public final Set<Edge<T>> inEdges;
          public final Set<Edge<T>> outEdges;
  
          public Node(T value) {
              this.value = value;
              inEdges = new HashSet<Edge<T>>();
              outEdges = new HashSet<Edge<T>>();
          }
  
          public Node<T> addEdge(Node<T> node) {
              Edge<T> e = new Edge<T>(this, node);
              outEdges.add(e);
              node.inEdges.add(e);
              return this;
          }
  
          @Override
          public String toString() {
              return value.toString();
          }
      }
  
      private static class Edge<T> {
          public final Node<T> from;
          public final Node<T> to;
  
          public Edge(Node<T> from, Node<T> to) {
              this.from = from;
              this.to = to;
          }
  
          @SuppressWarnings("unchecked")
          @Override
          public boolean equals(Object obj) {
              Edge<T> e = (Edge<T>) obj;
              return e.from == from && e.to == to;
          }
      }
  
  }