[120] | 1 | /** |
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| 2 | * Licensed to the Apache Software Foundation (ASF) under one |
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| 3 | * or more contributor license agreements. See the NOTICE file |
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| 4 | * distributed with this work for additional information |
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| 5 | * regarding copyright ownership. The ASF licenses this file |
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| 6 | * to you under the Apache License, Version 2.0 (the |
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| 7 | * "License"); you may not use this file except in compliance |
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| 8 | * with the License. You may obtain a copy of the License at |
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| 9 | * |
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| 10 | * http://www.apache.org/licenses/LICENSE-2.0 |
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| 11 | * |
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| 12 | * Unless required by applicable law or agreed to in writing, software |
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| 13 | * distributed under the License is distributed on an "AS IS" BASIS, |
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| 14 | * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. |
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| 15 | * See the License for the specific language governing permissions and |
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| 16 | * limitations under the License. |
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| 17 | */ |
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| 18 | package org.apache.hadoop.util; |
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| 19 | |
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| 20 | import java.util.Iterator; |
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| 21 | import java.util.Map; |
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| 22 | import java.util.NavigableMap; |
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| 23 | import java.util.NoSuchElementException; |
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| 24 | |
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| 25 | /** Provide an cyclic {@link Iterator} for a {@link NavigableMap}. |
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| 26 | * The {@link Iterator} navigates the entries of the map |
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| 27 | * according to the map's ordering. |
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| 28 | * If the {@link Iterator} hits the last entry of the map, |
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| 29 | * it will then continue from the first entry. |
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| 30 | */ |
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| 31 | public class CyclicIteration<K, V> implements Iterable<Map.Entry<K, V>> { |
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| 32 | private final NavigableMap<K, V> navigablemap; |
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| 33 | private final NavigableMap<K, V> tailmap; |
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| 34 | |
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| 35 | /** Construct an {@link Iterable} object, |
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| 36 | * so that an {@link Iterator} can be created |
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| 37 | * for iterating the given {@link NavigableMap}. |
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| 38 | * The iteration begins from the starting key exclusively. |
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| 39 | */ |
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| 40 | public CyclicIteration(NavigableMap<K, V> navigablemap, K startingkey) { |
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| 41 | if (navigablemap == null || navigablemap.isEmpty()) { |
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| 42 | this.navigablemap = null; |
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| 43 | this.tailmap = null; |
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| 44 | } |
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| 45 | else { |
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| 46 | this.navigablemap = navigablemap; |
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| 47 | this.tailmap = navigablemap.tailMap(startingkey, false); |
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| 48 | } |
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| 49 | } |
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| 50 | |
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| 51 | /** {@inheritDoc} */ |
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| 52 | public Iterator<Map.Entry<K, V>> iterator() { |
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| 53 | return new CyclicIterator(); |
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| 54 | } |
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| 55 | |
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| 56 | /** An {@link Iterator} for {@link CyclicIteration}. */ |
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| 57 | private class CyclicIterator implements Iterator<Map.Entry<K, V>> { |
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| 58 | private boolean hasnext; |
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| 59 | private Iterator<Map.Entry<K, V>> i; |
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| 60 | /** The first entry to begin. */ |
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| 61 | private final Map.Entry<K, V> first; |
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| 62 | /** The next entry. */ |
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| 63 | private Map.Entry<K, V> next; |
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| 64 | |
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| 65 | private CyclicIterator() { |
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| 66 | hasnext = navigablemap != null; |
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| 67 | if (hasnext) { |
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| 68 | i = tailmap.entrySet().iterator(); |
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| 69 | first = nextEntry(); |
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| 70 | next = first; |
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| 71 | } |
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| 72 | else { |
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| 73 | i = null; |
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| 74 | first = null; |
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| 75 | next = null; |
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| 76 | } |
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| 77 | } |
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| 78 | |
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| 79 | private Map.Entry<K, V> nextEntry() { |
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| 80 | if (!i.hasNext()) { |
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| 81 | i = navigablemap.entrySet().iterator(); |
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| 82 | } |
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| 83 | return i.next(); |
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| 84 | } |
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| 85 | |
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| 86 | /** {@inheritDoc} */ |
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| 87 | public boolean hasNext() { |
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| 88 | return hasnext; |
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| 89 | } |
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| 90 | |
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| 91 | /** {@inheritDoc} */ |
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| 92 | public Map.Entry<K, V> next() { |
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| 93 | if (!hasnext) { |
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| 94 | throw new NoSuchElementException(); |
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| 95 | } |
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| 96 | |
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| 97 | final Map.Entry<K, V> curr = next; |
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| 98 | next = nextEntry(); |
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| 99 | hasnext = !next.equals(first); |
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| 100 | return curr; |
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| 101 | } |
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| 102 | |
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| 103 | /** Not supported */ |
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| 104 | public void remove() { |
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| 105 | throw new UnsupportedOperationException("Not supported"); |
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| 106 | } |
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| 107 | } |
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| 108 | } |
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