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/* * @(#)EnumSyntax.java 1.6 05/11/17 * * Copyright 2006 Sun Microsystems, Inc. All rights reserved. * SUN PROPRIETARY/CONFIDENTIAL. Use is subject to license terms. */ package javax.print.attribute; import java.io.InvalidObjectException; import java.io.ObjectStreamException; import java.io.Serializable; /** * Class EnumSyntax is an abstract base class providing the common * implementation of all "type safe enumeration" objects. An enumeration class * (which extends class EnumSyntax) provides a group of enumeration values * (objects) that are singleton instances of the enumeration class; for example: * <PRE> * public class Bach extends EnumSyntax { * public static final Bach JOHANN_SEBASTIAN = new Bach(0); * public static final Bach WILHELM_FRIEDEMANN = new Bach(1); * public static final Bach CARL_PHILIP_EMMANUEL = new Bach(2); * public static final Bach JOHANN_CHRISTIAN = new Bach(3); * public static final Bach P_D_Q = new Bach(4); * * private static final String[] stringTable = { * "Johann Sebastian Bach", * "Wilhelm Friedemann Bach", * "Carl Philip Emmanuel Bach", * "Johann Christian Bach", * "P.D.Q. Bach" * }; * * protected String[] getStringTable() { * return stringTable; * } * * private static final Bach[] enumValueTable = { * JOHANN_SEBASTIAN, * WILHELM_FRIEDEMANN, * CARL_PHILIP_EMMANUEL, * JOHANN_CHRISTIAN, * P_D_Q * }; * * protected EnumSyntax[] getEnumValueTable() { * return enumValueTable; * } * } * </PRE> * You can then write code that uses the <CODE>==</CODE> and <CODE>!=</CODE> * operators to test enumeration values; for example: * <PRE> * Bach theComposer; * . . . * if (theComposer == Bach.JOHANN_SEBASTIAN) { * System.out.println ("The greatest composer of all time!"); * } * </PRE> * The <CODE>equals()</CODE> method for an enumeration class just does a test * for identical objects (<CODE>==</CODE>). * <P> * You can convert an enumeration value to a string by calling {@link * #toString() <CODE>toString()</CODE>}. The string is obtained from a table * supplied by the enumeration class. * <P> * Under the hood, an enumeration value is just an integer, a different integer * for each enumeration value within an enumeration class. You can get an * enumeration value's integer value by calling {@link #getValue() * <CODE>getValue()</CODE>}. An enumeration value's integer value is established * when it is constructed (see {@link #EnumSyntax(int) * <CODE>EnumSyntax(int)</CODE>}). Since the constructor is protected, the only * possible enumeration values are the singleton objects declared in the * enumeration class; additional enumeration values cannot be created at run * time. * <P> * You can define a subclass of an enumeration class that extends it with * additional enumeration values. The subclass's enumeration values' integer * values need not be distinct from the superclass's enumeration values' integer * values; the <CODE>==</CODE>, <CODE>!=</CODE>, <CODE>equals()</CODE>, and * <CODE>toString()</CODE> methods will still work properly even if the subclass * uses some of the same integer values as the superclass. However, the * application in which the enumeration class and subclass are used may need to * have distinct integer values in the superclass and subclass. * <P> * * @author David Mendenhall * @author Alan Kaminsky */ public abstract class EnumSyntax implements Serializable, Cloneable { private static final long serialVersionUID = -2739521845085831642L; /** * This enumeration value's integer value. * @serial */ private int value; /** * Construct a new enumeration value with the given integer value. * * @param value Integer value. */ protected EnumSyntax(int value) { this.value = value; } /** * Returns this enumeration value's integer value. * @return the value */ public int getValue() { return value; } /** * Returns a clone of this enumeration value, which to preserve the * semantics of enumeration values is the same object as this enumeration * value. */ public Object clone() { return this; } /** * Returns a hash code value for this enumeration value. The hash code is * just this enumeration value's integer value. */ public int hashCode() { return value; } /** * Returns a string value corresponding to this enumeration value. */ public String toString() { String[] theTable = getStringTable(); int theIndex = value - getOffset(); return theTable != null && theIndex >= 0 && theIndex < theTable.length ? theTable[theIndex] : Integer.toString (value); } /** * During object input, convert this deserialized enumeration instance to * the proper enumeration value defined in the enumeration attribute class. * * @return The enumeration singleton value stored at index * <I>i</I>-<I>L</I> in the enumeration value table returned by * {@link #getEnumValueTable() <CODE>getEnumValueTable()</CODE>}, * where <I>i</I> is this enumeration value's integer value and * <I>L</I> is the value returned by {@link #getOffset() * <CODE>getOffset()</CODE>}. * * @throws ObjectStreamException if the stream can't be deserialised * @throws InvalidObjectException * Thrown if the enumeration value table is null, this enumeration * value's integer value does not correspond to an element in the * enumeration value table, or the corresponding element in the * enumeration value table is null. (Note: {@link * java.io.InvalidObjectException InvalidObjectException} is a subclass * of {@link java.io.ObjectStreamException ObjectStreamException}, which * <CODE>readResolve()</CODE> is declared to throw.) */ protected Object readResolve() throws ObjectStreamException { EnumSyntax[] theTable = getEnumValueTable(); if (theTable == null) { throw new InvalidObjectException( "Null enumeration value table for class " + getClass()); } int theOffset = getOffset(); int theIndex = value - theOffset; if (0 > theIndex || theIndex >= theTable.length) { throw new InvalidObjectException ("Integer value = " + value + " not in valid range " + theOffset + ".." + (theOffset + theTable.length - 1) + "for class " + getClass()); } EnumSyntax result = theTable[theIndex]; if (result == null) { throw new InvalidObjectException ("No enumeration value for integer value = " + value + "for class " + getClass()); } return result; } // Hidden operations to be implemented in a subclass. /** * Returns the string table for this enumeration value's enumeration class. * The enumeration class's integer values are assumed to lie in the range * <I>L</I>..<I>L</I>+<I>N</I>-1, where <I>L</I> is the value returned by * {@link #getOffset() <CODE>getOffset()</CODE>} and <I>N</I> is the length * of the string table. The element in the string table at index * <I>i</I>-<I>L</I> is the value returned by {@link #toString() * <CODE>toString()</CODE>} for the enumeration value whose integer value * is <I>i</I>. If an integer within the above range is not used by any * enumeration value, leave the corresponding table element null. * <P> * The default implementation returns null. If the enumeration class (a * subclass of class EnumSyntax) does not override this method to return a * non-null string table, and the subclass does not override the {@link * #toString() <CODE>toString()</CODE>} method, the base class {@link * #toString() <CODE>toString()</CODE>} method will return just a string * representation of this enumeration value's integer value. * @return the string table */ protected String[] getStringTable() { return null; } /** * Returns the enumeration value table for this enumeration value's * enumeration class. The enumeration class's integer values are assumed to * lie in the range <I>L</I>..<I>L</I>+<I>N</I>-1, where <I>L</I> is the * value returned by {@link #getOffset() <CODE>getOffset()</CODE>} and * <I>N</I> is the length of the enumeration value table. The element in the * enumeration value table at index <I>i</I>-<I>L</I> is the enumeration * value object whose integer value is <I>i</I>; the {@link #readResolve() * <CODE>readResolve()</CODE>} method needs this to preserve singleton * semantics during deserialization of an enumeration instance. If an * integer within the above range is not used by any enumeration value, * leave the corresponding table element null. * <P> * The default implementation returns null. If the enumeration class (a * subclass of class EnumSyntax) does not override this method to return * a non-null enumeration value table, and the subclass does not override * the {@link #readResolve() <CODE>readResolve()</CODE>} method, the base * class {@link #readResolve() <CODE>readResolve()</CODE>} method will throw * an exception whenever an enumeration instance is deserialized from an * object input stream. * @return the value table */ protected EnumSyntax[] getEnumValueTable() { return null; } /** * Returns the lowest integer value used by this enumeration value's * enumeration class. * <P> * The default implementation returns 0. If the enumeration class (a * subclass of class EnumSyntax) uses integer values starting at other than * 0, override this method in the subclass. * @return the offset of the lowest enumeration value. */ protected int getOffset() { return 0; } }