code: ///////////////////////////////////////////////////////////////////////////
  //                   __                _      _   ________               //
  //                  / /   ____  ____ _(_)____/ | / / ____/               //
  //                 / /   / __ \/ __ `/ / ___/  |/ / / __                 //
  //                / /___/ /_/ / /_/ / / /__/ /|  / /_/ /                 //
  //               /_____/\____/\__, /_/\___/_/ |_/\____/                  //
  //                           /____/                                      //
  //                                                                       //
  //               The Next Generation Logic Library                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  //                                                                       //
  //  Copyright 2015-20xx Christoph Zengler                                //
  //                                                                       //
  //  Licensed under the Apache License, Version 2.0 (the "License");      //
  //  you may not use this file except in compliance with the License.     //
  //  You may obtain a copy of the License at                              //
  //                                                                       //
  //  http://www.apache.org/licenses/LICENSE-2.0                           //
  //                                                                       //
  //  Unless required by applicable law or agreed to in writing, software  //
  //  distributed under the License is distributed on an "AS IS" BASIS,    //
  //  WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or      //
  //  implied.  See the License for the specific language governing        //
  //  permissions and limitations under the License.                       //
  //                                                                       //
  ///////////////////////////////////////////////////////////////////////////
  
  package org.logicng.datastructures.ubtrees;
  
  import java.util.Objects;
  import java.util.SortedMap;
  import java.util.SortedSet;
  import java.util.TreeMap;
  
  /**
   * A node in a UBTree, holding a comparable element.
   * @param <T> The element type of the node, must be comparable
   * @version 2.0.0
   * @since 1.5.0
   */
  public final class UBNode<T extends Comparable<T>> {
  
      private final T element;
      private final SortedMap<T, UBNode<T>> children;
      private SortedSet<T> set;
  
      /**
       * Constructs a new UB Tree node with the given element.
       * @param element the node's element
       */
      UBNode(final T element) {
          this.element = element;
          this.children = new TreeMap<>();
      }
  
      /**
       * Returns the element of this node.
       * @return the element of this node.
       */
      T element() {
          return this.element;
      }
  
      /**
       * Returns the set of this node.  If this node is a terminal node, it holds a set
       * of the UB Tree.  In this case these methods returns this set, otherwise it returns
       * {@code null}.
       * @return the set of this node if it is a terminal node, {@code null} otherwise
       */
      SortedSet<T> set() {
          return this.set;
      }
  
      /**
       * Returns all children of this node.
       * @return a mapping from element to its node - all of which are children of the current node
       */
      SortedMap<T, UBNode<T>> children() {
          return this.children;
      }
  
      /**
       * Returns whether this node is a terminal node or not.
       * @return {@code true} if this is a terminal node, {@code false} otherwise
       */
      boolean isEndOfPath() {
          return this.set != null;
      }
  
      /**
       * Sets a set for this node and therefore this node is a terminal node.
       * @param set the set for this node
       */
      void setEndSet(final SortedSet<T> set) {
          this.set = set;
      }
  
      @Override
      public boolean equals(final Object o) {
          if (this == o) {
              return true;
          }
          if (o == null || getClass() != o.getClass()) {
              return false;
          }
          final UBNode<?> ubNode = (UBNode<?>) o;
          return Objects.equals(this.element, ubNode.element) &&
                  Objects.equals(this.children, ubNode.children) &&
                  Objects.equals(this.set, ubNode.set);
      }
  
      @Override
      public int hashCode() {
          return Objects.hash(this.element, this.children, this.set);
      }
  
      @Override
      public String toString() {
          return "UBNode{" +
                  "element=" + this.element +
                  ", children=" + this.children +
                  ", set=" + this.set +
                  '}';
      }
  }
  