/*
* @(#)EnumSyntax.java 1.5 04/01/07
*
* Copyright 2004 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;
}
}
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