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.Collection;
  import java.util.Iterator;
  
  import org.apache.tools.ant.types.Resource;
  
  /**
   * Base class for a ResourceCollection that wraps a single nested
   * ResourceCollection.
   * @since Ant 1.7
   */
  public abstract class BaseResourceCollectionWrapper
      extends AbstractResourceCollectionWrapper {
  
      private Collection<Resource> coll = null;
  
      @Override
      protected Iterator<Resource> createIterator() {
          return cacheCollection().iterator();
      }
  
      @Override
      protected int getSize() {
          return cacheCollection().size();
      }
  
      /**
       * Template method for subclasses to return a Collection of Resources.
       * @return Collection.
       */
      protected abstract Collection<Resource> getCollection();
  
      private synchronized Collection<Resource> cacheCollection() {
          if (coll == null || !isCache()) {
              coll = getCollection();
          }
          return coll;
      }
  
  }
  