/*

  * 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.giraph.utils;

 import org.apache.hadoop.io.WritableComparable;

 /**

  * Common implementation for VertexIdEdgeIterator, VertexIdMessageIterator

  * and VertexIdMessageBytesIterator.

  *

  * @param <I> Vertex id

  */

 public interface VertexIdIterator<I extends WritableComparable> {

   /**

    * Returns true if the iteration has more elements.

    *

    * @return True if the iteration has more elements.

    */

   boolean hasNext();

   /**

    * Moves to the next element in the iteration.

    */

   void next();

   /**

    * Get the current vertex id.  Ihis object's contents are only guaranteed

    * until next() is called.  To take ownership of this object call

    * releaseCurrentVertexId() after getting a reference to this object.

    *

    * @return Current vertex id

    */

   I getCurrentVertexId();

   /**

    * The backing store of the current vertex id is now released.

    * Further calls to getCurrentVertexId () without calling next()

    * will return null.

    *

    * @return Current vertex id that was released

    */

   I releaseCurrentVertexId();

 }