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/*

* Copyright (c) 1995, 2004, Oracle and/or its affiliates. All rights reserved.

* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.

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*/

package java.util;

/**

* The <code>Dictionary</code> class is the abstract parent of any

* class, such as <code>Hashtable</code>, which maps keys to values.

* Every key and every value is an object. In any one <tt>Dictionary</tt>

* object, every key is associated with at most one value. Given a

* <tt>Dictionary</tt> and a key, the associated element can be looked up.

* Any non-<code>null</code> object can be used as a key and as a value.

* <p>

* As a rule, the <code>equals</code> 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NOTE: This class is obsolete.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>

*

* @author unascribed

* @see java.util.Map

* @see java.lang.Object#equals(java.lang.Object)

* @see java.lang.Object#hashCode()

* @see java.util.Hashtable

* @since JDK1.0

*/

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.

*/

abstract public int size();

/**

* Tests if this dictionary maps no keys to value. The general contract

* for the <tt>isEmpty</tt> method is that the result is true if and only

* if this dictionary contains no entries.

*

* @return <code>true</code> if this dictionary maps no keys to values;

* <code>false</code> otherwise.

*/

abstract public boolean isEmpty();

/**

* Returns an enumeration of the keys in this dictionary. The general

* contract for the keys method is that an <tt>Enumeration</tt> 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

*/

abstract public Enumeration<K> keys();

/**

* Returns an enumeration of the values in this dictionary. The general

* contract for the <tt>elements</tt> method is that an

* <tt>Enumeration</tt> 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

*/

abstract public Enumeration<V> elements();

/**

* Returns the value to which the key is mapped in this dictionary.

* The general contract for the <tt>isEmpty</tt> method is that if this

* dictionary contains an entry for the specified key, the associated

* value is returned; otherwise, <tt>null</tt> is returned.

*

* @return the value to which the key is mapped in this dictionary;

* @param key a key in this dictionary.

* <code>null</code> if the key is not mapped to any value in

* this dictionary.

* @exception NullPointerException if the <tt>key</tt> is <tt>null</tt>.

* @see java.util.Dictionary#put(java.lang.Object, java.lang.Object)

*/

abstract public V get(Object key);

/**

* Maps the specified <code>key</code> to the specified

* <code>value</code> in this dictionary. Neither the key nor the

* value can be <code>null</code>.

* <p>

* If this dictionary already contains an entry for the specified

* <tt>key</tt>, the value already in this dictionary for that

* <tt>key</tt> is returned, after modifying the entry to contain the

* new element. <p>If this dictionary does not already have an entry

* for the specified <tt>key</tt>, an entry is created for the

* specified <tt>key</tt> and <tt>value</tt>, and <tt>null</tt> is

* returned.

* <p>

* The <code>value</code> can be retrieved by calling the

* <code>get</code> method with a <code>key</code> that is equal to

* the original <code>key</code>.

*

* @param key the hashtable key.

* @param value the value.

* @return the previous value to which the <code>key</code> was mapped

* in this dictionary, or <code>null</code> if the key did not

* have a previous mapping.

* @exception NullPointerException if the <code>key</code> or

* <code>value</code> is <code>null</code>.

* @see java.lang.Object#equals(java.lang.Object)

* @see java.util.Dictionary#get(java.lang.Object)

*/

abstract public V put(K key, V value);

/**

* Removes the <code>key</code> (and its corresponding

* <code>value</code>) from this dictionary. This method does nothing

* if the <code>key</code> is not in this dictionary.

*

* @param key the key that needs to be removed.

* @return the value to which the <code>key</code> had been mapped in this

* dictionary, or <code>null</code> if the key did not have a

* mapping.

* @exception NullPointerException if <tt>key</tt> is <tt>null</tt>.

*/

abstract public V remove(Object key);

}