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Dictionary.java
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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NOTE: This class is obsolete.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);
}