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VertexIdIterator xref
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1   /*
2    * Licensed to the Apache Software Foundation (ASF) under one
3    * or more contributor license agreements.  See the NOTICE file
4    * distributed with this work for additional information
5    * regarding copyright ownership.  The ASF licenses this file
6    * to you under the Apache License, Version 2.0 (the
7    * "License"); you may not use this file except in compliance
8    * with the License.  You may obtain a copy of the License at
9    *
10   *     http://www.apache.org/licenses/LICENSE-2.0
11   *
12   * Unless required by applicable law or agreed to in writing, software
13   * distributed under the License is distributed on an "AS IS" BASIS,
14   * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
15   * See the License for the specific language governing permissions and
16   * limitations under the License.
17   */
18  
19  package org.apache.giraph.utils;
20  
21  import org.apache.hadoop.io.WritableComparable;
22  
23  /**
24   * Common implementation for VertexIdEdgeIterator, VertexIdMessageIterator
25   * and VertexIdMessageBytesIterator.
26   *
27   * @param <I> Vertex id
28   */
29  public interface VertexIdIterator<I extends WritableComparable> {
30    /**
31     * Returns true if the iteration has more elements.
32     *
33     * @return True if the iteration has more elements.
34     */
35    boolean hasNext();
36  
37    /**
38     * Moves to the next element in the iteration.
39     */
40    void next();
41  
42    /**
43     * Get the current vertex id.  Ihis object's contents are only guaranteed
44     * until next() is called.  To take ownership of this object call
45     * releaseCurrentVertexId() after getting a reference to this object.
46     *
47     * @return Current vertex id
48     */
49    I getCurrentVertexId();
50  
51    /**
52     * The backing store of the current vertex id is now released.
53     * Further calls to getCurrentVertexId () without calling next()
54     * will return null.
55     *
56     * @return Current vertex id that was released
57     */
58    I releaseCurrentVertexId();
59  }
60