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
   *
   *    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.apache.kafka.streams.state.internals;
  
  import org.apache.kafka.streams.KeyValue;
  import org.apache.kafka.streams.state.KeyValueIterator;
  import org.apache.kafka.streams.state.WindowStoreIterator;
  
  import java.util.NoSuchElementException;
  
  class KeyValueIterators {
  
      private static class EmptyKeyValueIterator<K, V> implements KeyValueIterator<K, V> {
  
          @Override
          public void close() {
          }
  
          @Override
          public K peekNextKey() {
              throw new NoSuchElementException();
          }
  
          @Override
          public boolean hasNext() {
              return false;
          }
  
          @Override
          public KeyValue<K, V> next() {
              throw new NoSuchElementException();
          }
  
      }
  
      private static class EmptyWindowStoreIterator<V> extends EmptyKeyValueIterator<Long, V>
          implements WindowStoreIterator<V> {
      }
  
      private static final KeyValueIterator<?, ?> EMPTY_ITERATOR = new EmptyKeyValueIterator<>();
      private static final WindowStoreIterator<?> EMPTY_WINDOW_STORE_ITERATOR = new EmptyWindowStoreIterator<>();
  
  
      @SuppressWarnings("unchecked")
      static <K, V> KeyValueIterator<K, V> emptyIterator() {
          return (KeyValueIterator<K, V>) EMPTY_ITERATOR;
      }
  
      @SuppressWarnings("unchecked")
      static <V> WindowStoreIterator<V> emptyWindowStoreIterator() {
          return (WindowStoreIterator<V>) EMPTY_WINDOW_STORE_ITERATOR;
      }
  }
  