| /** |
| * 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.hadoop.util; |
| |
| import java.util.Iterator; |
| import java.util.Map; |
| import java.util.NavigableMap; |
| import java.util.NoSuchElementException; |
| |
| import org.apache.hadoop.classification.InterfaceAudience; |
| import org.apache.hadoop.classification.InterfaceStability; |
| |
| /** Provide an cyclic {@link Iterator} for a {@link NavigableMap}. |
| * The {@link Iterator} navigates the entries of the map |
| * according to the map's ordering. |
| * If the {@link Iterator} hits the last entry of the map, |
| * it will then continue from the first entry. |
| */ |
| @InterfaceAudience.Private |
| @InterfaceStability.Unstable |
| public class CyclicIteration<K, V> implements Iterable<Map.Entry<K, V>> { |
| private final NavigableMap<K, V> navigablemap; |
| private final NavigableMap<K, V> tailmap; |
| |
| /** Construct an {@link Iterable} object, |
| * so that an {@link Iterator} can be created |
| * for iterating the given {@link NavigableMap}. |
| * The iteration begins from the starting key exclusively. |
| */ |
| public CyclicIteration(NavigableMap<K, V> navigablemap, K startingkey) { |
| if (navigablemap == null || navigablemap.isEmpty()) { |
| this.navigablemap = null; |
| this.tailmap = null; |
| } |
| else { |
| this.navigablemap = navigablemap; |
| this.tailmap = navigablemap.tailMap(startingkey, false); |
| } |
| } |
| |
| /** {@inheritDoc} */ |
| public Iterator<Map.Entry<K, V>> iterator() { |
| return new CyclicIterator(); |
| } |
| |
| /** An {@link Iterator} for {@link CyclicIteration}. */ |
| private class CyclicIterator implements Iterator<Map.Entry<K, V>> { |
| private boolean hasnext; |
| private Iterator<Map.Entry<K, V>> i; |
| /** The first entry to begin. */ |
| private final Map.Entry<K, V> first; |
| /** The next entry. */ |
| private Map.Entry<K, V> next; |
| |
| private CyclicIterator() { |
| hasnext = navigablemap != null; |
| if (hasnext) { |
| i = tailmap.entrySet().iterator(); |
| first = nextEntry(); |
| next = first; |
| } |
| else { |
| i = null; |
| first = null; |
| next = null; |
| } |
| } |
| |
| private Map.Entry<K, V> nextEntry() { |
| if (!i.hasNext()) { |
| i = navigablemap.entrySet().iterator(); |
| } |
| return i.next(); |
| } |
| |
| /** {@inheritDoc} */ |
| public boolean hasNext() { |
| return hasnext; |
| } |
| |
| /** {@inheritDoc} */ |
| public Map.Entry<K, V> next() { |
| if (!hasnext) { |
| throw new NoSuchElementException(); |
| } |
| |
| final Map.Entry<K, V> curr = next; |
| next = nextEntry(); |
| hasnext = !next.equals(first); |
| return curr; |
| } |
| |
| /** Not supported */ |
| public void remove() { |
| throw new UnsupportedOperationException("Not supported"); |
| } |
| } |
| } |