001: /*
002: * @(#)Dictionary.java 1.22 06/10/10
003: *
004: * Copyright 1990-2006 Sun Microsystems, Inc. All Rights Reserved.
005: * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER
006: *
007: * This program is free software; you can redistribute it and/or
008: * modify it under the terms of the GNU General Public License version
009: * 2 only, as published by the Free Software Foundation.
010: *
011: * This program is distributed in the hope that it will be useful, but
012: * WITHOUT ANY WARRANTY; without even the implied warranty of
013: * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
014: * General Public License version 2 for more details (a copy is
015: * included at /legal/license.txt).
016: *
017: * You should have received a copy of the GNU General Public License
018: * version 2 along with this work; if not, write to the Free Software
019: * Foundation, Inc., 51 Franklin St, Fifth Floor, Boston, MA
020: * 02110-1301 USA
021: *
022: * Please contact Sun Microsystems, Inc., 4150 Network Circle, Santa
023: * Clara, CA 95054 or visit www.sun.com if you need additional
024: * information or have any questions.
025: *
026: */
027:
028: package java.util;
029:
030: /**
031: * The <code>Dictionary</code> class is the abstract parent of any
032: * class, such as <code>Hashtable</code>, which maps keys to values.
033: * Every key and every value is an object. In any one <tt>Dictionary</tt>
034: * object, every key is associated with at most one value. Given a
035: * <tt>Dictionary</tt> and a key, the associated element can be looked up.
036: * Any non-<code>null</code> object can be used as a key and as a value.
037: * <p>
038: * As a rule, the <code>equals</code> method should be used by
039: * implementations of this class to decide if two keys are the same.
040: * <p>
041: * <strong>NOTE: This class is obsolete. New implementations should
042: * implement the Map interface, rather than extending this class.</strong>
043: *
044: * @author unascribed
045: * @version 1.15, 02/02/00
046: * @see java.util.Map
047: * @see java.lang.Object#equals(java.lang.Object)
048: * @see java.lang.Object#hashCode()
049: * @see java.util.Hashtable
050: * @since JDK1.0
051: */
052: public abstract class Dictionary {
053: /**
054: * Sole constructor. (For invocation by subclass constructors, typically
055: * implicit.)
056: */
057: public Dictionary() {
058: }
059:
060: /**
061: * Returns the number of entries (dinstint keys) in this dictionary.
062: *
063: * @return the number of keys in this dictionary.
064: */
065: abstract public int size();
066:
067: /**
068: * Tests if this dictionary maps no keys to value. The general contract
069: * for the <tt>isEmpty</tt> method is that the result is true if and only
070: * if this dictionary contains no entries.
071: *
072: * @return <code>true</code> if this dictionary maps no keys to values;
073: * <code>false</code> otherwise.
074: */
075: abstract public boolean isEmpty();
076:
077: /**
078: * Returns an enumeration of the keys in this dictionary. The general
079: * contract for the keys method is that an <tt>Enumeration</tt> object
080: * is returned that will generate all the keys for which this dictionary
081: * contains entries.
082: *
083: * @return an enumeration of the keys in this dictionary.
084: * @see java.util.Dictionary#elements()
085: * @see java.util.Enumeration
086: */
087: abstract public Enumeration keys();
088:
089: /**
090: * Returns an enumeration of the values in this dictionary. The general
091: * contract for the <tt>elements</tt> method is that an
092: * <tt>Enumeration</tt> is returned that will generate all the elements
093: * contained in entries in this dictionary.
094: *
095: * @return an enumeration of the values in this dictionary.
096: * @see java.util.Dictionary#keys()
097: * @see java.util.Enumeration
098: */
099: abstract public Enumeration elements();
100:
101: /**
102: * Returns the value to which the key is mapped in this dictionary.
103: * The general contract for the <tt>isEmpty</tt> method is that if this
104: * dictionary contains an entry for the specified key, the associated
105: * value is returned; otherwise, <tt>null</tt> is returned.
106: *
107: * @return the value to which the key is mapped in this dictionary;
108: * @param key a key in this dictionary.
109: * <code>null</code> if the key is not mapped to any value in
110: * this dictionary.
111: * @exception NullPointerException if the <tt>key</tt> is <tt>null</tt>.
112: * @see java.util.Dictionary#put(java.lang.Object, java.lang.Object)
113: */
114: abstract public Object get(Object key);
115:
116: /**
117: * Maps the specified <code>key</code> to the specified
118: * <code>value</code> in this dictionary. Neither the key nor the
119: * value can be <code>null</code>.
120: * <p>
121: * If this dictionary already contains an entry for the specified
122: * <tt>key</tt>, the value already in this dictionary for that
123: * <tt>key</tt> is returned, after modifying the entry to contain the
124: * new element. <p>If this dictionary does not already have an entry
125: * for the specified <tt>key</tt>, an entry is created for the
126: * specified <tt>key</tt> and <tt>value</tt>, and <tt>null</tt> is
127: * returned.
128: * <p>
129: * The <code>value</code> can be retrieved by calling the
130: * <code>get</code> method with a <code>key</code> that is equal to
131: * the original <code>key</code>.
132: *
133: * @param key the hashtable key.
134: * @param value the value.
135: * @return the previous value to which the <code>key</code> was mapped
136: * in this dictionary, or <code>null</code> if the key did not
137: * have a previous mapping.
138: * @exception NullPointerException if the <code>key</code> or
139: * <code>value</code> is <code>null</code>.
140: * @see java.lang.Object#equals(java.lang.Object)
141: * @see java.util.Dictionary#get(java.lang.Object)
142: */
143: abstract public Object put(Object key, Object value);
144:
145: /**
146: * Removes the <code>key</code> (and its corresponding
147: * <code>value</code>) from this dictionary. This method does nothing
148: * if the <code>key</code> is not in this dictionary.
149: *
150: * @param key the key that needs to be removed.
151: * @return the value to which the <code>key</code> had been mapped in this
152: * dictionary, or <code>null</code> if the key did not have a
153: * mapping.
154: * @exception NullPointerException if <tt>key</tt> is <tt>null</tt>.
155: */
156: abstract public Object remove(Object key);
157: }
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