Mega Code Archive
Cyclic Iteration
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/**
* 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.
*/
import java.util.Iterator;
import java.util.Map;
import java.util.NoSuchElementException;
import java.util.SortedMap;
/** Provide an cyclic {@link Iterator} for a {@link SortedMap}.
* 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.
*/
public class CyclicIteration<K, V> implements Iterable<Map.Entry<K, V>> {
private final SortedMap<K, V> navigablemap;
private final SortedMap<K, V> tailmap;
private final K startingkey;
/** Construct an {@link Iterable} object,
* so that an {@link Iterator} can be created
* for iterating the given {@link SortedMap}.
* The iteration begins from the starting key exclusively.
*/
public CyclicIteration(SortedMap<K, V> navigablemap, K startingkey) {
this.startingkey = startingkey;
if (navigablemap == null || navigablemap.isEmpty()) {
this.navigablemap = null;
this.tailmap = null;
}
else {
this.navigablemap = navigablemap;
this.tailmap = navigablemap.tailMap(startingkey);
}
}
/** {@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();
Map.Entry<K, V> e = nextEntry();
if (e.getKey().equals(startingkey)) {
e = nextEntry();
}
first = e;
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");
}
}
}
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