content: /*
   *  Licensed to the Apache Software Foundation (ASF) under one or more
   *  contributor license agreements.  See the NOTICE file distributed with
   *  this work for additional information regarding copyright ownership.
   *  The ASF licenses this file to You 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
   *
   *      https://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.apache.tools.ant.types.resources;
  
  import java.util.ArrayList;
  import java.util.Collection;
  import java.util.HashSet;
  import java.util.List;
  import java.util.Set;
  
  import org.apache.tools.ant.BuildException;
  import org.apache.tools.ant.types.Resource;
  import org.apache.tools.ant.types.ResourceCollection;
  
  /**
   * ResourceCollection representing the difference between
   * two or more nested ResourceCollections.
   * @since Ant 1.7
   */
  public class Difference extends BaseResourceCollectionContainer {
  
      /**
       * Calculate the difference of the nested ResourceCollections.
       * @return a Collection of Resources.
       */
      @Override
      protected Collection<Resource> getCollection() {
          List<ResourceCollection> rcs = getResourceCollections();
          int size = rcs.size();
          if (size < 2) {
              throw new BuildException(
                  "The difference of %d resource %s is undefined.", size,
                  size == 1 ? "collection" : "collections");
          }
          Set<Resource> hs = new HashSet<>();
          List<Resource> al = new ArrayList<>();
          for (ResourceCollection rc : rcs) {
              for (Resource r : rc) {
                  if (hs.add(r)) {
                      al.add(r);
                  } else {
                      al.remove(r);
                  }
              }
          }
          return al;
      }
  
  }
  