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    1   /*
    2    * Copyright (c) 1995, 2004, Oracle and/or its affiliates. All rights reserved.
    3    * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
    4    *
    5    * This code is free software; you can redistribute it and/or modify it
    6    * under the terms of the GNU General Public License version 2 only, as
    7    * published by the Free Software Foundation.  Oracle designates this
    8    * particular file as subject to the "Classpath" exception as provided
    9    * by Oracle in the LICENSE file that accompanied this code.
   10    *
   11    * This code is distributed in the hope that it will be useful, but WITHOUT
   12    * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
   13    * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
   14    * version 2 for more details (a copy is included in the LICENSE file that
   15    * accompanied this code).
   16    *
   17    * You should have received a copy of the GNU General Public License version
   18    * 2 along with this work; if not, write to the Free Software Foundation,
   19    * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
   20    *
   21    * Please contact Oracle, 500 Oracle Parkway, Redwood Shores, CA 94065 USA
   22    * or visit www.oracle.com if you need additional information or have any
   23    * questions.
   24    */
   25   
   26   package java.util;
   27   
   28   /**
   29    * The <code>Dictionary</code> class is the abstract parent of any
   30    * class, such as <code>Hashtable</code>, which maps keys to values.
   31    * Every key and every value is an object. In any one <tt>Dictionary</tt>
   32    * object, every key is associated with at most one value. Given a
   33    * <tt>Dictionary</tt> and a key, the associated element can be looked up.
   34    * Any non-<code>null</code> object can be used as a key and as a value.
   35    * <p>
   36    * As a rule, the <code>equals</code> method should be used by
   37    * implementations of this class to decide if two keys are the same.
   38    * <p>
   39    * <strong>NOTE: This class is obsolete.  New implementations should
   40    * implement the Map interface, rather than extending this class.</strong>
   41    *
   42    * @author  unascribed
   43    * @see     java.util.Map
   44    * @see     java.lang.Object#equals(java.lang.Object)
   45    * @see     java.lang.Object#hashCode()
   46    * @see     java.util.Hashtable
   47    * @since   JDK1.0
   48    */
   49   public abstract
   50   class Dictionary<K,V> {
   51       /**
   52        * Sole constructor.  (For invocation by subclass constructors, typically
   53        * implicit.)
   54        */
   55       public Dictionary() {
   56       }
   57   
   58       /**
   59        * Returns the number of entries (distinct keys) in this dictionary.
   60        *
   61        * @return  the number of keys in this dictionary.
   62        */
   63       abstract public int size();
   64   
   65       /**
   66        * Tests if this dictionary maps no keys to value. The general contract
   67        * for the <tt>isEmpty</tt> method is that the result is true if and only
   68        * if this dictionary contains no entries.
   69        *
   70        * @return  <code>true</code> if this dictionary maps no keys to values;
   71        *          <code>false</code> otherwise.
   72        */
   73       abstract public boolean isEmpty();
   74   
   75       /**
   76        * Returns an enumeration of the keys in this dictionary. The general
   77        * contract for the keys method is that an <tt>Enumeration</tt> object
   78        * is returned that will generate all the keys for which this dictionary
   79        * contains entries.
   80        *
   81        * @return  an enumeration of the keys in this dictionary.
   82        * @see     java.util.Dictionary#elements()
   83        * @see     java.util.Enumeration
   84        */
   85       abstract public Enumeration<K> keys();
   86   
   87       /**
   88        * Returns an enumeration of the values in this dictionary. The general
   89        * contract for the <tt>elements</tt> method is that an
   90        * <tt>Enumeration</tt> is returned that will generate all the elements
   91        * contained in entries in this dictionary.
   92        *
   93        * @return  an enumeration of the values in this dictionary.
   94        * @see     java.util.Dictionary#keys()
   95        * @see     java.util.Enumeration
   96        */
   97       abstract public Enumeration<V> elements();
   98   
   99       /**
  100        * Returns the value to which the key is mapped in this dictionary.
  101        * The general contract for the <tt>isEmpty</tt> method is that if this
  102        * dictionary contains an entry for the specified key, the associated
  103        * value is returned; otherwise, <tt>null</tt> is returned.
  104        *
  105        * @return  the value to which the key is mapped in this dictionary;
  106        * @param   key   a key in this dictionary.
  107        *          <code>null</code> if the key is not mapped to any value in
  108        *          this dictionary.
  109        * @exception NullPointerException if the <tt>key</tt> is <tt>null</tt>.
  110        * @see     java.util.Dictionary#put(java.lang.Object, java.lang.Object)
  111        */
  112       abstract public V get(Object key);
  113   
  114       /**
  115        * Maps the specified <code>key</code> to the specified
  116        * <code>value</code> in this dictionary. Neither the key nor the
  117        * value can be <code>null</code>.
  118        * <p>
  119        * If this dictionary already contains an entry for the specified
  120        * <tt>key</tt>, the value already in this dictionary for that
  121        * <tt>key</tt> is returned, after modifying the entry to contain the
  122        *  new element. <p>If this dictionary does not already have an entry
  123        *  for the specified <tt>key</tt>, an entry is created for the
  124        *  specified <tt>key</tt> and <tt>value</tt>, and <tt>null</tt> is
  125        *  returned.
  126        * <p>
  127        * The <code>value</code> can be retrieved by calling the
  128        * <code>get</code> method with a <code>key</code> that is equal to
  129        * the original <code>key</code>.
  130        *
  131        * @param      key     the hashtable key.
  132        * @param      value   the value.
  133        * @return     the previous value to which the <code>key</code> was mapped
  134        *             in this dictionary, or <code>null</code> if the key did not
  135        *             have a previous mapping.
  136        * @exception  NullPointerException  if the <code>key</code> or
  137        *               <code>value</code> is <code>null</code>.
  138        * @see        java.lang.Object#equals(java.lang.Object)
  139        * @see        java.util.Dictionary#get(java.lang.Object)
  140        */
  141       abstract public V put(K key, V value);
  142   
  143       /**
  144        * Removes the <code>key</code> (and its corresponding
  145        * <code>value</code>) from this dictionary. This method does nothing
  146        * if the <code>key</code> is not in this dictionary.
  147        *
  148        * @param   key   the key that needs to be removed.
  149        * @return  the value to which the <code>key</code> had been mapped in this
  150        *          dictionary, or <code>null</code> if the key did not have a
  151        *          mapping.
  152        * @exception NullPointerException if <tt>key</tt> is <tt>null</tt>.
  153        */
  154       abstract public V remove(Object key);
  155   }

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