https://lucene.apache.org/lucene-parent/lucene-core: Apache Lucene Java Core (The Apache Software Foundation) 
/*
 * 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.lucene.util;


import java.io.IOException;


A simple iterator interface for BytesRef iteration. 
/**
 * A simple iterator interface for {@link BytesRef} iteration.
 */
public interface BytesRefIterator {

  
Increments the iteration to the next BytesRef in the iterator. Returns the resulting BytesRef or null if the end of
the iterator is reached. The returned BytesRef may be re-used across calls
to next. After this method returns null, do not call it again: the results
are undefined.

Throws:
Returns:the next BytesRef in the iterator or null if
        the end of the iterator is reached.
/**
   * Increments the iteration to the next {@link BytesRef} in the iterator.
   * Returns the resulting {@link BytesRef} or <code>null</code> if the end of
   * the iterator is reached. The returned BytesRef may be re-used across calls
   * to next. After this method returns null, do not call it again: the results
   * are undefined.
   * 
   * @return the next {@link BytesRef} in the iterator or <code>null</code> if
   *         the end of the iterator is reached.
   * @throws IOException If there is a low-level I/O error.
   */
  BytesRef next() throws IOException;
  
  
Singleton BytesRefIterator that iterates over 0 BytesRefs. 
/** Singleton BytesRefIterator that iterates over 0 BytesRefs. */
  BytesRefIterator EMPTY = () -> null;
}