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
005This file is part of GNU Classpath.
006
007GNU Classpath is free software; you can redistribute it and/or modify
008it under the terms of the GNU General Public License as published by
009the Free Software Foundation; either version 2, or (at your option)
010any later version.
011
012GNU Classpath is distributed in the hope that it will be useful, but
013WITHOUT ANY WARRANTY; without even the implied warranty of
014MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
015General Public License for more details.
016
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018along with GNU Classpath; see the file COPYING.  If not, write to the
019Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
02002110-1301 USA.
021
022Linking this library statically or dynamically with other modules is
023making a combined work based on this library.  Thus, the terms and
024conditions of the GNU General Public License cover the whole
025combination.
026
027As a special exception, the copyright holders of this library give you
028permission to link this library with independent modules to produce an
029executable, regardless of the license terms of these independent
030modules, and to copy and distribute the resulting executable under
031terms of your choice, provided that you also meet, for each linked
032independent module, the terms and conditions of the license of that
033module.  An independent module is a module which is not derived from
034or based on this library.  If you modify this library, you may extend
035this exception to your version of the library, but you are not
036obligated to do so.  If you do not wish to do so, delete this
037exception statement from your version. */
038
039
040package 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 */
060public 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