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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;

import java.util.SortedMap;

/**
 * Defines the interface for a prefix tree, an ordered tree data structure. For
 * more information, see Tries.
 *
 * @param  the type of the keys in this map
 * @param  the type of the values in this map
 * @since 4.0
 */
public interface Trie extends IterableSortedMap {

    /**
     * Returns a view of this {@link Trie} of all elements that are prefixed
     * by the given key.
     * 
     * In a {@link Trie} with fixed size keys, this is essentially a
     * {@link #get(Object)} operation.
     * 
     * For example, if the {@link Trie} contains 'Anna', 'Anael',
     * 'Analu', 'Andreas', 'Andrea', 'Andres', and 'Anatole', then
     * a lookup of 'And' would return 'Andreas', 'Andrea', and 'Andres'.
     *
     * @param key  the key used in the search
     * @return a {@link SortedMap} view of this {@link Trie} with all elements whose
     *   key is prefixed by the search key
     */
    SortedMap prefixMap(K key);

}