    001/*
    002 * Licensed to the Apache Software Foundation (ASF) under one or more
    003 * contributor license agreements.  See the NOTICE file distributed with
    004 * this work for additional information regarding copyright ownership.
    005 * The ASF licenses this file to You under the Apache License, Version 2.0
    006 * (the "License"); you may not use this file except in compliance with
    007 * the License.  You may obtain a copy of the License at
    008 *
    009 *      https://www.apache.org/licenses/LICENSE-2.0
    010 *
    011 * Unless required by applicable law or agreed to in writing, software
    012 * distributed under the License is distributed on an "AS IS" BASIS,
    013 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
    014 * See the License for the specific language governing permissions and
    015 * limitations under the License.
    016 */
    017
    018package org.apache.commons.collections4;
    019
    020import java.util.Collection;
    021import java.util.Map;
    022import java.util.Set;
    023
    024/**
    025 * The "read" subset of the {@link Map} interface.
    026 *
    027 * @param <K> The type of the keys in this map
    028 * @param <V> The type of the values in this map
    029 * @since 4.0
    030 * @see Put
    031 */
    032public interface Get<K, V> {
    033
    034    /**
    035     * Tests for presence of a given key.
    036     *
    037     * @param key key whose presence in this map is to be tested.
    038     * @return {@code true} if this map contains a mapping for the specified key.
    039     * @see Map#containsKey(Object)
    040     */
    041    boolean containsKey(Object key);
    042
    043    /**
    044     * Tests for presence of a given value.
    045     *
    046     * @param value value whose presence in this map is to be tested.
    047     * @return {@code true} if this map maps one or more keys to the specified value.
    048     * @see Map#containsValue(Object)
    049     */
    050    boolean containsValue(Object value);
    051
    052    /**
    053     * Gets a set view of the mappings contained in this map.
    054     *
    055     * @return A set view of the mappings contained in this map.
    056     * @see Map#entrySet()
    057     */
    058    Set<Map.Entry<K, V>> entrySet();
    059
    060    /**
    061     * Gets a value at a given key.
    062     *
    063     * @param key The key whose associated value is to be returned.
    064     * @return The value to which the specified key is mapped, or {@code null} if this map contains no mapping for the key.
    065     * @see Map#get(Object)
    066     */
    067    V get(Object key);
    068
    069    /**
    070     * Tests whether this instance contains any key-value mappings.
    071     *
    072     * @return {@code true} if this map contains no key-value mappings.
    073     * @see Map#isEmpty()
    074     */
    075    boolean isEmpty();
    076
    077    /**
    078     * Gets a view of the keys contained in this map.
    079     *
    080     * @return A set view of the keys contained in this map.
    081     * @see Map#keySet()
    082     */
    083    Set<K> keySet();
    084
    085    /**
    086     * Remove a key-value mappings.
    087     *
    088     * @param key key whose mapping is to be removed from the map.
    089     * @return The previous value associated with {@code key}, or {@code null} if there was no mapping for {@code key}.
    090     * @see Map#remove(Object)
    091     */
    092    V remove(Object key);
    093
    094    /**
    095     * Gets the number of key-value mappings in this map.
    096     *
    097     * @return The number of key-value mappings in this map.
    098     * @see Map#size()
    099     */
    100    int size();
    101
    102    /**
    103     * Gets a a collection view of the values contained in this map.
    104     *
    105     * @return A collection view of the values contained in this map.
    106     * @see Map#values()
    107     */
    108    Collection<V> values();
    109}