EnumSyntax.java

/* EnumSyntax.java -- 
   Copyright (C) 2003, 2005 Free Software Foundation, Inc.

This file is part of GNU Classpath.

GNU Classpath is free software; you can redistribute it and/or modify
it under the terms of the GNU General Public License as published by
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package javax.print.attribute;

import java.io.InvalidObjectException;
import java.io.ObjectStreamException;
import java.io.Serializable;

/**
 * <code>EnumSyntax</code> is the abstract base class of all enumeration
 * classes in the Java Print Service API. 
 * <p>
 * Every enumeration class which extends from EnumSyntax provides several 
 * enumeration objects as singletons of its class.
 * </p>
 * <p>
 * Notes for implementing subclasses:
 * <ul>
 *   <li>
 *     The values of all enumeration singelton instances have to be in a 
 *     sequence which may start at any value. See: {@link #getOffset()}
 *   </li>
 *   <li>
 *     Subclasses have to override {@link #getEnumValueTable()} and should
 *     override {@link #getStringTable()} for correct serialization.
 *   </li>
 * </ul>
 * </p>
 * Example: 
 * <pre> 
 * public class PrinterState extends EnumSyntax
 * {
 *   public static final PrinterState IDLE = new PrinterState(1);
 *   public static final PrinterState PROCESSING = new PrinterState(2);
 *   public static final PrinterState STOPPED = new PrinterState(3);
 * 
 *   protected PrinterState(int value)
 *   {
 *     super(value);
 *   }
 * 
 *   // Overridden because values start not at zero !
 *   protected int getOffset()
 *   {
 *     return 1;
 *   }
 * 
 *   private static final String[] stringTable = { "idle", "processing", 
 *                                                 "stopped" };
 * 
 *   protected String[] getStringTable()
 *   {
 *     return stringTable;
 *   }
 * 
 *   private static final PrinterState[] enumValueTable = { IDLE, 
 *                                             PROCESSING, STOPPED};
 * 
 *   protected EnumSyntax[] getEnumValueTable()
 *   {
 *     return enumValueTable;
 *   }
 * }
 * </pre>
 * 
 * @author Michael Koch (konqueror@gmx.de)
 * @author Wolfgang Baer (WBaer@gmx.de)
 */
public abstract class EnumSyntax implements Cloneable, Serializable
{
  private static final long serialVersionUID = -2739521845085831642L;
  
  private int value;

  /**
   * Creates a <code>EnumSyntax</code> object.
   *
   * @param value the value to set.
   */
  protected EnumSyntax(int value)
  {
    this.value = value;
  }

  /**
   * Returns the value of this enumeration object.
   *
   * @return The value.
   */
  public int getValue()
  {
    return value;
  }

  /**
   * Clones this object.
   *
   * @return A clone of this object.
   */
  public Object clone()
  {
    try
      {
        return super.clone();
      }
    catch (CloneNotSupportedException e)
      {
        // Cannot happen as we implement java.lang.Cloneable.
        return null;
      }
  }

  /**
   * Returns the hashcode for this object. 
   * The hashcode is the value of this enumeration object.
   *
   * @return The hashcode.
   */
  public int hashCode()
  {
    return value;
  }

  /**
   * Returns the string representation for this object.
   * The string value from <code>getStringTable()</code> method is returned
   * if subclasses override this method. Otherwise the value of this object
   * as a string is returned.
   *
   * @return The string representation.
   */
  public String toString()
  {
    int index = value - getOffset();
    String[] table = getStringTable();

    if (table != null
        && index >= 0
        && index < table.length)
      return table[index];
    
    return "" + value;
  }

  /**
   * Returns a table with the enumeration values represented as strings
   * for this object.
   *
   * The default implementation just returns null. Subclasses should
   * override this method.
   *
   * @return The enumeration values as strings.
   */
  protected String[] getStringTable()
  {
    return null;
  }

  /**
   * Needed for singelton semantics during deserialisation.
   * 
   * Subclasses must not override this class. Subclasses have to override
   * <code>getEnumValueTable()</code> and should override 
   * <code>getStringTable()</code> for correct serialization.
   * 
   * @return The Object at index <code>value - getOffset()</code> 
   *         in getEnumValueTable.
   * @throws ObjectStreamException if getEnumValueTable() returns null.
   */
  protected Object readResolve() throws ObjectStreamException
  {
    EnumSyntax[] table = getEnumValueTable();
    if (table == null)
      throw new InvalidObjectException("Null enumeration value table "
                                       + "for class "
                                       + this.getClass().toString());

    return table[value - getOffset()];
  }

  /**
   * Returns a table with the enumeration values for this object.
   *
   * The default implementation just returns null. Subclasses have to
   * to override this method for serialization.
   *
   * @return The enumeration values.
   */
  protected EnumSyntax[] getEnumValueTable()
  {
    return null;
  }

  /**
   * Returns the lowest used value by the enumerations of this class. 
   * 
   * The default implementation returns 0. This is enough if enumerations
   * start with a zero value. Otherwise subclasses need to override this 
   * method for serialization and return the lowest value they use.
   * .
   * @return The lowest used value used.
   */
  protected int getOffset()
  {
    return 0;
  }
}