001/* EnumSyntax.java --
002   Copyright (C) 2003, 2005 Free Software Foundation, Inc.
003
004This file is part of GNU Classpath.
005
006GNU Classpath is free software; you can redistribute it and/or modify
007it under the terms of the GNU General Public License as published by
008the Free Software Foundation; either version 2, or (at your option)
009any later version.
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013MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
014General Public License for more details.
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017along with GNU Classpath; see the file COPYING.  If not, write to the
018Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
01902110-1301 USA.
020
021Linking this library statically or dynamically with other modules is
022making a combined work based on this library.  Thus, the terms and
023conditions of the GNU General Public License cover the whole
024combination.
025
026As a special exception, the copyright holders of this library give you
027permission to link this library with independent modules to produce an
028executable, regardless of the license terms of these independent
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030terms of your choice, provided that you also meet, for each linked
031independent module, the terms and conditions of the license of that
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034this exception to your version of the library, but you are not
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036exception statement from your version. */
037
038package javax.print.attribute;
039
040import java.io.InvalidObjectException;
041import java.io.ObjectStreamException;
042import java.io.Serializable;
043
044/**
045 * <code>EnumSyntax</code> is the abstract base class of all enumeration
046 * classes in the Java Print Service API.
047 * <p>
048 * Every enumeration class which extends from EnumSyntax provides several
049 * enumeration objects as singletons of its class.
050 * </p>
051 * <p>
052 * Notes for implementing subclasses:
053 * <ul>
054 *   <li>
055 *     The values of all enumeration singelton instances have to be in a
056 *     sequence which may start at any value. See: {@link #getOffset()}
057 *   </li>
058 *   <li>
059 *     Subclasses have to override {@link #getEnumValueTable()} and should
060 *     override {@link #getStringTable()} for correct serialization.
061 *   </li>
062 * </ul>
063 * </p>
064 * Example:
065 * <pre>
066 * public class PrinterState extends EnumSyntax
067 * {
068 *   public static final PrinterState IDLE = new PrinterState(1);
069 *   public static final PrinterState PROCESSING = new PrinterState(2);
070 *   public static final PrinterState STOPPED = new PrinterState(3);
071 *
072 *   protected PrinterState(int value)
073 *   {
074 *     super(value);
075 *   }
076 *
077 *   // Overridden because values start not at zero !
078 *   protected int getOffset()
079 *   {
080 *     return 1;
081 *   }
082 *
083 *   private static final String[] stringTable = { "idle", "processing",
084 *                                                 "stopped" };
085 *
086 *   protected String[] getStringTable()
087 *   {
088 *     return stringTable;
089 *   }
090 *
091 *   private static final PrinterState[] enumValueTable = { IDLE,
092 *                                             PROCESSING, STOPPED};
093 *
094 *   protected EnumSyntax[] getEnumValueTable()
095 *   {
096 *     return enumValueTable;
097 *   }
098 * }
099 * </pre>
100 *
101 * @author Michael Koch (konqueror@gmx.de)
102 * @author Wolfgang Baer (WBaer@gmx.de)
103 */
104public abstract class EnumSyntax implements Cloneable, Serializable
105{
106  private static final long serialVersionUID = -2739521845085831642L;
107
108  private int value;
109
110  /**
111   * Creates a <code>EnumSyntax</code> object.
112   *
113   * @param value the value to set.
114   */
115  protected EnumSyntax(int value)
116  {
117    this.value = value;
118  }
119
120  /**
121   * Returns the value of this enumeration object.
122   *
123   * @return The value.
124   */
125  public int getValue()
126  {
127    return value;
128  }
129
130  /**
131   * Clones this object.
132   *
133   * @return A clone of this object.
134   */
135  public Object clone()
136  {
137    try
138      {
139        return super.clone();
140      }
141    catch (CloneNotSupportedException e)
142      {
143        // Cannot happen as we implement java.lang.Cloneable.
144        return null;
145      }
146  }
147
148  /**
149   * Returns the hashcode for this object.
150   * The hashcode is the value of this enumeration object.
151   *
152   * @return The hashcode.
153   */
154  public int hashCode()
155  {
156    return value;
157  }
158
159  /**
160   * Returns the string representation for this object.
161   * The string value from <code>getStringTable()</code> method is returned
162   * if subclasses override this method. Otherwise the value of this object
163   * as a string is returned.
164   *
165   * @return The string representation.
166   */
167  public String toString()
168  {
169    int index = value - getOffset();
170    String[] table = getStringTable();
171
172    if (table != null
173        && index >= 0
174        && index < table.length)
175      return table[index];
176
177    return "" + value;
178  }
179
180  /**
181   * Returns a table with the enumeration values represented as strings
182   * for this object.
183   *
184   * The default implementation just returns null. Subclasses should
185   * override this method.
186   *
187   * @return The enumeration values as strings.
188   */
189  protected String[] getStringTable()
190  {
191    return null;
192  }
193
194  /**
195   * Needed for singelton semantics during deserialisation.
196   *
197   * Subclasses must not override this class. Subclasses have to override
198   * <code>getEnumValueTable()</code> and should override
199   * <code>getStringTable()</code> for correct serialization.
200   *
201   * @return The Object at index <code>value - getOffset()</code>
202   *         in getEnumValueTable.
203   * @throws ObjectStreamException if getEnumValueTable() returns null.
204   */
205  protected Object readResolve() throws ObjectStreamException
206  {
207    EnumSyntax[] table = getEnumValueTable();
208    if (table == null)
209      throw new InvalidObjectException("Null enumeration value table "
210                                       + "for class "
211                                       + this.getClass().toString());
212
213    return table[value - getOffset()];
214  }
215
216  /**
217   * Returns a table with the enumeration values for this object.
218   *
219   * The default implementation just returns null. Subclasses have to
220   * to override this method for serialization.
221   *
222   * @return The enumeration values.
223   */
224  protected EnumSyntax[] getEnumValueTable()
225  {
226    return null;
227  }
228
229  /**
230   * Returns the lowest used value by the enumerations of this class.
231   *
232   * The default implementation returns 0. This is enough if enumerations
233   * start with a zero value. Otherwise subclasses need to override this
234   * method for serialization and return the lowest value they use.
235   * .
236   * @return The lowest used value used.
237   */
238  protected int getOffset()
239  {
240    return 0;
241  }
242}