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The Apache Commons Collections package contains types that extend and augment the Java Collections Framework.
There is a newer version: 4.5.0-M1
/*
 * 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.commons.collections4.map;

import java.util.Comparator;
import java.util.Iterator;
import java.util.ListIterator;
import java.util.Map;
import java.util.Set;
import java.util.SortedMap;

import org.apache.commons.collections4.IterableSortedMap;
import org.apache.commons.collections4.OrderedMapIterator;
import org.apache.commons.collections4.iterators.ListIteratorWrapper;

/**
 * Provides a base decorator that enables additional functionality to be added
 * to a Map via decoration.
 * 
 * Methods are forwarded directly to the decorated map.
 * 
 * 
 * This implementation does not perform any special processing with the map views.
 * Instead it simply returns the set/collection from the wrapped map. This may be
 * undesirable, for example if you are trying to write a validating implementation
 * it would provide a loophole around the validation.
 * But, you might want that loophole, so this class is kept simple.
 * 
 *
 * @param  the type of the keys in the map
 * @param  the type of the values in the map
 * @since 3.0
 */
public abstract class AbstractSortedMapDecorator extends AbstractMapDecorator implements
        IterableSortedMap {

    /**
     * Constructor only used in deserialization, do not use otherwise.
     * @since 3.1
     */
    protected AbstractSortedMapDecorator() {
        super();
    }

    /**
     * Constructor that wraps (not copies).
     *
     * @param map  the map to decorate, must not be null
     * @throws NullPointerException if the map is null
     */
    public AbstractSortedMapDecorator(final SortedMap map) {
        super(map);
    }

    /**
     * Gets the map being decorated.
     *
     * @return the decorated map
     */
    @Override
    protected SortedMap decorated() {
        return (SortedMap) super.decorated();
    }

    //-----------------------------------------------------------------------
    @Override
    public Comparator comparator() {
        return decorated().comparator();
    }

    @Override
    public K firstKey() {
        return decorated().firstKey();
    }

    @Override
    public K lastKey() {
        return decorated().lastKey();
    }

    @Override
    public SortedMap subMap(final K fromKey, final K toKey) {
        return decorated().subMap(fromKey, toKey);
    }

    @Override
    public SortedMap headMap(final K toKey) {
        return decorated().headMap(toKey);
    }

    @Override
    public SortedMap tailMap(final K fromKey) {
        return decorated().tailMap(fromKey);
    }

    @Override
    public K previousKey(final K key) {
        final SortedMap headMap = headMap(key);
        return headMap.isEmpty() ? null : headMap.lastKey();
    }

    @Override
    public K nextKey(final K key) {
        final Iterator it = tailMap(key).keySet().iterator();
        it.next();
        return it.hasNext() ? it.next() : null;
    }

    /**
     * {@inheritDoc}
     */
    @Override
    public OrderedMapIterator mapIterator() {
        return new SortedMapIterator<>(entrySet());
    }

    /**
     * OrderedMapIterator implementation.
     *
     * @param   the key type
     * @param   the value type
     */
    protected static class SortedMapIterator extends EntrySetToMapIteratorAdapter
            implements OrderedMapIterator {

        /**
         * Create a new AbstractSortedMapDecorator.SortedMapIterator.
         * @param entrySet  the entrySet to iterate
         */
        protected SortedMapIterator(final Set> entrySet) {
            super(entrySet);
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public synchronized void reset() {
            super.reset();
            iterator = new ListIteratorWrapper<>(iterator);
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public boolean hasPrevious() {
            return ((ListIterator>) iterator).hasPrevious();
        }

        /**
         * {@inheritDoc}
         */
        @Override
        public K previous() {
            entry = ((ListIterator>) iterator).previous();
            return getKey();
        }
    }
}