libjava/java/util/Dictionary.java

   1 /* Dictionary.java -- an abstract (and essentially worthless)
   2    class which is Hashtable's superclass
   3    Copyright (C) 1998, 2001, 2002 Free Software Foundation, Inc.
   4
   5 This file is part of GNU Classpath.
   6
   7 GNU Classpath is free software; you can redistribute it and/or modify
   8 it under the terms of the GNU General Public License as published by
   9 the Free Software Foundation; either version 2, or (at your option)
  10 any later version.
  11
  12 GNU Classpath is distributed in the hope that it will be useful, but
  13 WITHOUT ANY WARRANTY; without even the implied warranty of
  14 MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
  15 General Public License for more details.
  16
  17 You should have received a copy of the GNU General Public License
  18 along with GNU Classpath; see the file COPYING.  If not, write to the
  19 Free Software Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA
  20 02111-1307 USA.
  21
  22 Linking this library statically or dynamically with other modules is
  23 making a combined work based on this library.  Thus, the terms and
  24 conditions of the GNU General Public License cover the whole
  25 combination.
  26
  27 As a special exception, the copyright holders of this library give you
  28 permission to link this library with independent modules to produce an
  29 executable, regardless of the license terms of these independent
  30 modules, and to copy and distribute the resulting executable under
  31 terms of your choice, provided that you also meet, for each linked
  32 independent module, the terms and conditions of the license of that
  33 module.  An independent module is a module which is not derived from
  34 or based on this library.  If you modify this library, you may extend
  35 this exception to your version of the library, but you are not
  36 obligated to do so.  If you do not wish to do so, delete this
  37 exception statement from your version. */
  38
  39
  40 package java.util;
  41
  42 /**
  43  * A Dictionary maps keys to values; <i>how</i> it does that is
  44  * implementation-specific.
  45  *
  46  * This is an abstract class which has really gone by the wayside.
  47  * People at Javasoft are probably embarrassed by it.  At this point,
  48  * it might as well be an interface rather than a class, but it remains
  49  * this poor, laughable skeleton for the sake of backwards compatibility.
  50  * At any rate, this was what came before the {@link Map} interface
  51  * in the Collections framework.
  52  *
  53  * @author Jon Zeppieri
  54  * @author Eric Blake (ebb9@email.byu.edu)
  55  * @see Map
  56  * @see Hashtable
  57  * @since 1.0
  58  * @status updated to 1.4
  59  */
  60 public abstract class Dictionary
  61 {
  62   // WARNING: Dictionary is a CORE class in the bootstrap cycle. See the
  63   // comments in vm/reference/java/lang/Runtime for implications of this fact.
  64
  65   /**
  66    * Sole constructor (often called implicitly).
  67    */
  68   public Dictionary()
  69   {
  70   }
  71
  72   /**
  73    * Returns an Enumeration of the values in this Dictionary.
  74    *
  75    * @return an Enumeration of the values
  76    * @see #keys()
  77    */
  78   public abstract Enumeration elements();
  79
  80   /**
  81    * Returns the value associated with the supplied key, or null
  82    * if no such value exists. Since Dictionaries are not allowed null keys
  83    * or elements, a null result always means the key is not present.
  84    *
  85    * @param key the key to use to fetch the value
  86    * @return the mapped value
  87    * @throws NullPointerException if key is null
  88    * @see #put(Object, Object)
  89    */
  90   public abstract Object get(Object key);
  91
  92   /**
  93    * Returns true when there are no elements in this Dictionary.
  94    *
  95    * @return <code>size() == 0</code>
  96    */
  97   public abstract boolean isEmpty();
  98
  99   /**
 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 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 Object put(Object key, Object 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 Object 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