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	/*
	* Copyright (c) 1995, 2020, Oracle and/or its affiliates. All rights reserved.
	* DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
	*
	* This code is free software; you can redistribute it and/or modify it
	* under the terms of the GNU General Public License version 2 only, as
	* published by the Free Software Foundation. Oracle designates this
	* particular file as subject to the "Classpath" exception as provided
	* by Oracle in the LICENSE file that accompanied this code.
	*
	* This code is distributed in the hope that it will be useful, but WITHOUT
	* ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
	* FITNESS FOR A PARTICULAR PURPOSE. See the GNU General Public License
	* version 2 for more details (a copy is included in the LICENSE file that
	* accompanied this code).
	*
	* You should have received a copy of the GNU General Public License version
	* 2 along with this work; if not, write to the Free Software Foundation,
	* Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
	*
	* Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
	* or visit www.oracle.com if you need additional information or have any
	* questions.
	*/

	package java.util;

	/**
	* The {@code Dictionary} class is the abstract parent of any
	* class, such as {@code Hashtable}, which maps keys to values.
	* Every key and every value is an object. In any one {@code Dictionary}
	* object, every key is associated with at most one value. Given a
	* {@code Dictionary} and a key, the associated element can be looked up.
	* Any non-{@code null} object can be used as a key and as a value.
	* <p>
	* As a rule, the {@code equals} method should be used by
	* implementations of this class to decide if two keys are the same.
	* <p>
	* <strong>NOTE: This class is obsolete. New implementations should
	* implement the Map interface, rather than extending this class.</strong>
	*
	* @see java.util.Map
	* @see java.lang.Object#equals(java.lang.Object)
	* @see java.lang.Object#hashCode()
	* @see java.util.Hashtable
	* @since 1.0
	*/
	public abstract
	class Dictionary<K,V> {
	/**
	* Sole constructor. (For invocation by subclass constructors, typically
	* implicit.)
	*/
	public Dictionary() {
	}

	/**
	* Returns the number of entries (distinct keys) in this dictionary.
	*
	* @return the number of keys in this dictionary.
	*/
	public abstract int size();

	/**
	* Tests if this dictionary maps no keys to value. The general contract
	* for the {@code isEmpty} method is that the result is true if and only
	* if this dictionary contains no entries.
	*
	* @return {@code true} if this dictionary maps no keys to values;
	* {@code false} otherwise.
	*/
	public abstract boolean isEmpty();

	/**
	* Returns an enumeration of the keys in this dictionary. The general
	* contract for the keys method is that an {@code Enumeration} object
	* is returned that will generate all the keys for which this dictionary
	* contains entries.
	*
	* @return an enumeration of the keys in this dictionary.
	* @see java.util.Dictionary#elements()
	* @see java.util.Enumeration
	*/
	public abstract Enumeration<K> keys();

	/**
	* Returns an enumeration of the values in this dictionary. The general
	* contract for the {@code elements} method is that an
	* {@code Enumeration} is returned that will generate all the elements
	* contained in entries in this dictionary.
	*
	* @return an enumeration of the values in this dictionary.
	* @see java.util.Dictionary#keys()
	* @see java.util.Enumeration
	*/
	public abstract Enumeration<V> elements();

	/**
	* Returns the value to which the key is mapped in this dictionary.
	* The general contract for the {@code isEmpty} method is that if this
	* dictionary contains an entry for the specified key, the associated
	* value is returned; otherwise, {@code null} is returned.
	*
	* @return the value to which the key is mapped in this dictionary;
	* @param key a key in this dictionary.
	* {@code null} if the key is not mapped to any value in
	* this dictionary.
	* @throws NullPointerException if the {@code key} is {@code null}.
	* @see java.util.Dictionary#put(java.lang.Object, java.lang.Object)
	*/
	public abstract V get(Object key);

	/**
	* Maps the specified {@code key} to the specified
	* {@code value} in this dictionary. Neither the key nor the
	* value can be {@code null}.
	* <p>
	* If this dictionary already contains an entry for the specified
	* {@code key}, the value already in this dictionary for that
	* {@code key} is returned, after modifying the entry to contain the
	* new element. <p>If this dictionary does not already have an entry
	* for the specified {@code key}, an entry is created for the
	* specified {@code key} and {@code value}, and {@code null} is
	* returned.
	* <p>
	* The {@code value} can be retrieved by calling the
	* {@code get} method with a {@code key} that is equal to
	* the original {@code key}.
	*
	* @param key the hashtable key.
	* @param value the value.
	* @return the previous value to which the {@code key} was mapped
	* in this dictionary, or {@code null} if the key did not
	* have a previous mapping.
	* @throws NullPointerException if the {@code key} or
	* {@code value} is {@code null}.
	* @see java.lang.Object#equals(java.lang.Object)
	* @see java.util.Dictionary#get(java.lang.Object)
	*/
	public abstract V put(K key, V value);

	/**
	* Removes the {@code key} (and its corresponding
	* {@code value}) from this dictionary. This method does nothing
	* if the {@code key} is not in this dictionary.
	*
	* @param key the key that needs to be removed.
	* @return the value to which the {@code key} had been mapped in this
	* dictionary, or {@code null} if the key did not have a
	* mapping.
	* @throws NullPointerException if {@code key} is {@code null}.
	*/
	public abstract V remove(Object key);
	}

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