001    /* EnumSyntax.java -- 
002       Copyright (C) 2003, 2005 Free Software Foundation, Inc.
003    
004    This file is part of GNU Classpath.
005    
006    GNU Classpath is free software; you can redistribute it and/or modify
007    it under the terms of the GNU General Public License as published by
008    the Free Software Foundation; either version 2, or (at your option)
009    any later version.
010    
011    GNU Classpath 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 for more details.
015    
016    You should have received a copy of the GNU General Public License
017    along with GNU Classpath; see the file COPYING.  If not, write to the
018    Free Software Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA
019    02110-1301 USA.
020    
021    Linking this library statically or dynamically with other modules is
022    making a combined work based on this library.  Thus, the terms and
023    conditions of the GNU General Public License cover the whole
024    combination.
025    
026    As a special exception, the copyright holders of this library give you
027    permission to link this library with independent modules to produce an
028    executable, regardless of the license terms of these independent
029    modules, and to copy and distribute the resulting executable under
030    terms of your choice, provided that you also meet, for each linked
031    independent module, the terms and conditions of the license of that
032    module.  An independent module is a module which is not derived from
033    or based on this library.  If you modify this library, you may extend
034    this exception to your version of the library, but you are not
035    obligated to do so.  If you do not wish to do so, delete this
036    exception statement from your version. */
037    
038    package javax.print.attribute;
039    
040    import java.io.InvalidObjectException;
041    import java.io.ObjectStreamException;
042    import 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     */
104    public 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    }