集合研究------Map

/* *  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 java.util;/** * A {@code Map} is a data structure consisting of a set of keys and values * in which each key is mapped to a single value.  The class of the objects * used as keys is declared when the {@code Map} is declared, as is the * class of the corresponding values. * <p> * A {@code Map} provides helper methods to iterate through all of the * keys contained in it, as well as various methods to access and update * the key/value pairs. */public interface Map<K,V> {    /**     * {@code Map.Entry} is a key/value mapping contained in a {@code Map}.     */    public static interface Entry<K,V> {        /**         * Compares the specified object to this {@code Map.Entry} and returns if they         * are equal. To be equal, the object must be an instance of {@code Map.Entry} and have the         * same key and value.         *         * @param object         *            the {@code Object} to compare with this {@code Object}.         * @return {@code true} if the specified {@code Object} is equal to this         *         {@code Map.Entry}, {@code false} otherwise.         * @see #hashCode()         */        public boolean equals(Object object);        /**         * Returns the key.         *         * @return the key         */        public K getKey();        /**         * Returns the value.         *         * @return the value         */        public V getValue();        /**         * Returns an integer hash code for the receiver. {@code Object} which are         * equal return the same value for this method.         *         * @return the receiver's hash code.         * @see #equals(Object)         */        public int hashCode();        /**         * Sets the value of this entry to the specified value, replacing any         * existing value.         *         * @param object         *            the new value to set.         * @return object the replaced value of this entry.         */        public V setValue(V object);    };    /**     * Removes all elements from this {@code Map}, leaving it empty.     *     * @throws UnsupportedOperationException     *                if removing elements from this {@code Map} is not supported.     * @see #isEmpty()     * @see #size()     */    public void clear();    /**     * Returns whether this {@code Map} contains the specified key.     *     * @param key     *            the key to search for.     * @return {@code true} if this map contains the specified key,     *         {@code false} otherwise.     */    public boolean containsKey(Object key);    /**     * Returns whether this {@code Map} contains the specified value.     *     * @param value     *            the value to search for.     * @return {@code true} if this map contains the specified value,     *         {@code false} otherwise.     */    public boolean containsValue(Object value);    /**     * Returns a {@code Set} containing all of the mappings in this {@code Map}. Each mapping is     * an instance of {@link Map.Entry}. As the {@code Set} is backed by this {@code Map},     * changes in one will be reflected in the other.     *     * @return a set of the mappings     */    public Set<Map.Entry<K,V>> entrySet();    /**     * Compares the argument to the receiver, and returns {@code true} if the     * specified object is a {@code Map} and both {@code Map}s contain the same mappings.     *     * @param object     *            the {@code Object} to compare with this {@code Object}.     * @return boolean {@code true} if the {@code Object} is the same as this {@code Object}     *         {@code false} if it is different from this {@code Object}.     * @see #hashCode()     * @see #entrySet()     */    public boolean equals(Object object);    /**     * Returns the value of the mapping with the specified key.     *     * @param key     *            the key.     * @return the value of the mapping with the specified key, or {@code null}     *         if no mapping for the specified key is found.     */    public V get(Object key);    /**     * Returns an integer hash code for the receiver. {@code Object}s which are equal     * return the same value for this method.     *     * @return the receiver's hash.     * @see #equals(Object)     */    public int hashCode();    /**     * Returns whether this map is empty.     *     * @return {@code true} if this map has no elements, {@code false}     *         otherwise.     * @see #size()     */    public boolean isEmpty();    /**     * Returns a set of the keys contained in this {@code Map}. The {@code Set} is backed by     * this {@code Map} so changes to one are reflected by the other. The {@code Set} does not     * support adding.     *     * @return a set of the keys.     */    public Set<K> keySet();    /**     * Maps the specified key to the specified value.     *     * @param key     *            the key.     * @param value     *            the value.     * @return the value of any previous mapping with the specified key or     *         {@code null} if there was no mapping. 也就是返回老（你将要替换的）的value，如果没有这样key，返回的是null。     * @throws UnsupportedOperationException     *                if adding to this {@code Map} is not supported.     * @throws ClassCastException     *                if the class of the key or value is inappropriate for     *                this {@code Map}.     * @throws IllegalArgumentException     *                if the key or value cannot be added to this {@code Map}.     * @throws NullPointerException     *                if the key or value is {@code null} and this {@code Map} does     *                not support {@code null} keys or values.

     *        */    public V put(K key, V value);    /**     * Copies every mapping in the specified {@code Map} to this {@code Map}.     *     * @param map     *            the {@code Map} to copy mappings from.     * @throws UnsupportedOperationException     *                if adding to this {@code Map} is not supported.     * @throws ClassCastException     *                if the class of a key or a value of the specified {@code Map} is     *                inappropriate for this {@code Map}.     * @throws IllegalArgumentException     *                if a key or value cannot be added to this {@code Map}.     * @throws NullPointerException     *                if a key or value is {@code null} and this {@code Map} does not     *                support {@code null} keys or values.     */    public void putAll(Map<? extends K,? extends V> map);    /**     * Removes a mapping with the specified key from this {@code Map}.     *     * @param key     *            the key of the mapping to remove.     * @return the value of the removed mapping or {@code null} if no mapping     *         for the specified key was found.     * @throws UnsupportedOperationException     *                if removing from this {@code Map} is not supported.     */    public V remove(Object key);    /**     * Returns the number of mappings in this {@code Map}.     *     * @return the number of mappings in this {@code Map}.     */    public int size();    /**     * Returns a {@code Collection} of the values contained in this {@code Map}. The {@code Collection}     * is backed by this {@code Map} so changes to one are reflected by the other. The     * {@code Collection} supports {@link Collection#remove}, {@link Collection#removeAll},     * {@link Collection#retainAll}, and {@link Collection#clear} operations,     * and it does not support {@link Collection#add} or {@link Collection#addAll} operations.     * <p>     * This method returns a {@code Collection} which is the subclass of     * {@link AbstractCollection}. The {@link AbstractCollection#iterator} method of this subclass returns a     * "wrapper object" over the iterator of this {@code Map}'s {@link #entrySet()}. The {@link AbstractCollection#size} method     * wraps this {@code Map}'s {@link #size} method and the {@link AbstractCollection#contains} method wraps this {@code Map}'s     * {@link #containsValue} method.     * <p>     * The collection is created when this method is called at first time and     * returned in response to all subsequent calls. This method may return     * different Collection when multiple calls to this method, since it has no     * synchronization performed.     *     * @return a collection of the values contained in this map.     */    public Collection<V> values();}