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   *  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
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   *    https://www.apache.org/licenses/LICENSE-2.0
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  package org.apache.cayenne.util;
  
  import java.io.Serializable;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.List;
  
  import org.apache.cayenne.QueryResponse;
  
  /**
   * A QueryResponse optimized to hold a single object or data row list.
   * 
   * @since 1.2
   */
  public class ListResponse implements QueryResponse, Serializable {
  
      protected List<?> objectList;
  
      protected transient int currentIndex;
  
      /**
       * Creates an empty response.
       */
      public ListResponse() {
          this.objectList = new ArrayList<>(1);
      }
  
      public ListResponse(Object object) {
          this.objectList = Collections.singletonList(object);
      }
  
      public ListResponse(List<?> objectList) {
          this.objectList = objectList;
      }
  
      public int size() {
          return 1;
      }
  
      public boolean isList() {
          if (currentIndex != 1) {
              throw new IndexOutOfBoundsException("Past iteration end: " + currentIndex);
          }
  
          return true;
      }
  
      public List<?> currentList() {
          if (currentIndex != 1) {
              throw new IndexOutOfBoundsException("Past iteration end: " + currentIndex);
          }
  
          return objectList;
      }
  
      public int[] currentUpdateCount() {
          throw new IllegalStateException("Current object is not an update count");
      }
  
      public boolean next() {
          return ++currentIndex <= 1;
      }
  
      public void reset() {
          // use a zero-based index, not -1, as this will simplify serialization handling
          currentIndex = 0;
      }
  
      public List<?> firstList() {
          return objectList;
      }
  
  }
  