001    /* Dictionary.java -- an abstract (and essentially worthless) 
002       class which is Hashtable's superclass
003       Copyright (C) 1998, 2001, 2002, 2004 Free Software Foundation, Inc.
004    
005    This file is part of GNU Classpath.
006    
007    GNU Classpath is free software; you can redistribute it and/or modify
008    it under the terms of the GNU General Public License as published by
009    the Free Software Foundation; either version 2, or (at your option)
010    any later version.
011    
012    GNU Classpath is distributed in the hope that it will be useful, but
013    WITHOUT ANY WARRANTY; without even the implied warranty of
014    MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
015    General Public License for more details.
016    
017    You should have received a copy of the GNU General Public License
018    along with GNU Classpath; see the file COPYING.  If not, write to the
019    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
020    02110-1301 USA.
021    
022    Linking this library statically or dynamically with other modules is
023    making a combined work based on this library.  Thus, the terms and
024    conditions of the GNU General Public License cover the whole
025    combination.
026    
027    As a special exception, the copyright holders of this library give you
028    permission to link this library with independent modules to produce an
029    executable, regardless of the license terms of these independent
030    modules, and to copy and distribute the resulting executable under
031    terms of your choice, provided that you also meet, for each linked
032    independent module, the terms and conditions of the license of that
033    module.  An independent module is a module which is not derived from
034    or based on this library.  If you modify this library, you may extend
035    this exception to your version of the library, but you are not
036    obligated to do so.  If you do not wish to do so, delete this
037    exception statement from your version. */
038    
039    
040    package java.util;
041    
042    /**
043     * A Dictionary maps keys to values; <i>how</i> it does that is
044     * implementation-specific.
045     * 
046     * This is an abstract class which has really gone by the wayside.
047     * People at Javasoft are probably embarrassed by it.  At this point,
048     * it might as well be an interface rather than a class, but it remains
049     * this poor, laughable skeleton for the sake of backwards compatibility.
050     * At any rate, this was what came before the {@link Map} interface 
051     * in the Collections framework.
052     *
053     * @author Jon Zeppieri
054     * @author Eric Blake (ebb9@email.byu.edu)
055     * @see Map
056     * @see Hashtable
057     * @since 1.0
058     * @status updated to 1.4
059     */
060    public abstract class Dictionary<K, V>
061    {
062      // WARNING: Dictionary is a CORE class in the bootstrap cycle. See the
063      // comments in vm/reference/java/lang/Runtime for implications of this fact.
064    
065      /**
066       * Sole constructor (often called implicitly).
067       */
068      public Dictionary()
069      {
070      }
071    
072      /**
073       * Returns an Enumeration of the values in this Dictionary.
074       *
075       * @return an Enumeration of the values
076       * @see #keys()
077       */
078      public abstract Enumeration<V> elements();
079    
080      /** 
081       * Returns the value associated with the supplied key, or null
082       * if no such value exists. Since Dictionaries are not allowed null keys
083       * or elements, a null result always means the key is not present.
084       *
085       * @param key the key to use to fetch the value
086       * @return the mapped value
087       * @throws NullPointerException if key is null
088       * @see #put(Object, Object)
089       */
090      public abstract V get(Object key);
091    
092      /**
093       * Returns true when there are no elements in this Dictionary.
094       *
095       * @return <code>size() == 0</code>
096       */
097      public abstract boolean isEmpty();
098    
099      /**
100       * Returns an Enumeration of the keys in this Dictionary
101       *
102       * @return an Enumeration of the keys
103       * @see #elements()
104       */
105      public abstract Enumeration<K> keys();
106    
107      /**
108       * Inserts a new value into this Dictionary, located by the
109       * supplied key. Dictionary does not support null keys or values, so
110       * a null return can safely be interpreted as adding a new key.
111       *
112       * @param key the key which locates the value
113       * @param value the value to put into the Dictionary
114       * @return the previous value of the key, or null if there was none
115       * @throws NullPointerException if key or value is null
116       * @see #get(Object)
117       */
118      public abstract V put(K key, V value);
119    
120      /**
121       * Removes from the Dictionary the value located by the given key. A null
122       * return safely means that the key was not mapped in the Dictionary.
123       *
124       * @param key the key used to locate the value to be removed
125       * @return the value associated with the removed key
126       * @throws NullPointerException if key is null
127       */
128      public abstract V remove(Object key);
129    
130      /**
131       * Returns the number of values currently in this Dictionary.
132       *
133       * @return the number of keys in the Dictionary
134       */
135      public abstract int size();
136    } // class Dictionary