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282 lines
10 KiB
282 lines
10 KiB
/*
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* Copyright (c) 2000, 2013, Oracle and/or its affiliates. All rights reserved.
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* ORACLE PROPRIETARY/CONFIDENTIAL. Use is subject to license terms.
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*
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*/
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package javax.print.attribute;
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import java.io.InvalidObjectException;
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import java.io.ObjectStreamException;
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import java.io.Serializable;
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/**
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* Class EnumSyntax is an abstract base class providing the common
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* implementation of all "type safe enumeration" objects. An enumeration class
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* (which extends class EnumSyntax) provides a group of enumeration values
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* (objects) that are singleton instances of the enumeration class; for example:
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* <PRE>
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* public class Bach extends EnumSyntax {
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* public static final Bach JOHANN_SEBASTIAN = new Bach(0);
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* public static final Bach WILHELM_FRIEDEMANN = new Bach(1);
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* public static final Bach CARL_PHILIP_EMMANUEL = new Bach(2);
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* public static final Bach JOHANN_CHRISTIAN = new Bach(3);
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* public static final Bach P_D_Q = new Bach(4);
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*
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* private static final String[] stringTable = {
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* "Johann Sebastian Bach",
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* "Wilhelm Friedemann Bach",
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* "Carl Philip Emmanuel Bach",
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* "Johann Christian Bach",
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* "P.D.Q. Bach"
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* };
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*
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* protected String[] getStringTable() {
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* return stringTable;
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* }
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*
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* private static final Bach[] enumValueTable = {
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* JOHANN_SEBASTIAN,
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* WILHELM_FRIEDEMANN,
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* CARL_PHILIP_EMMANUEL,
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* JOHANN_CHRISTIAN,
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* P_D_Q
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* };
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*
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* protected EnumSyntax[] getEnumValueTable() {
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* return enumValueTable;
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* }
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* }
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* </PRE>
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* You can then write code that uses the <CODE>==</CODE> and <CODE>!=</CODE>
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* operators to test enumeration values; for example:
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* <PRE>
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* Bach theComposer;
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* . . .
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* if (theComposer == Bach.JOHANN_SEBASTIAN) {
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* System.out.println ("The greatest composer of all time!");
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* }
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* </PRE>
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* The <CODE>equals()</CODE> method for an enumeration class just does a test
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* for identical objects (<CODE>==</CODE>).
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* <P>
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* You can convert an enumeration value to a string by calling {@link
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* #toString() toString()}. The string is obtained from a table
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* supplied by the enumeration class.
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* <P>
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* Under the hood, an enumeration value is just an integer, a different integer
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* for each enumeration value within an enumeration class. You can get an
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* enumeration value's integer value by calling {@link #getValue()
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* getValue()}. An enumeration value's integer value is established
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* when it is constructed (see {@link #EnumSyntax(int)
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* EnumSyntax(int)}). Since the constructor is protected, the only
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* possible enumeration values are the singleton objects declared in the
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* enumeration class; additional enumeration values cannot be created at run
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* time.
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* <P>
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* You can define a subclass of an enumeration class that extends it with
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* additional enumeration values. The subclass's enumeration values' integer
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* values need not be distinct from the superclass's enumeration values' integer
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* values; the <CODE>==</CODE>, <CODE>!=</CODE>, <CODE>equals()</CODE>, and
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* <CODE>toString()</CODE> methods will still work properly even if the subclass
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* uses some of the same integer values as the superclass. However, the
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* application in which the enumeration class and subclass are used may need to
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* have distinct integer values in the superclass and subclass.
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* <P>
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*
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* @author David Mendenhall
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* @author Alan Kaminsky
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*/
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public abstract class EnumSyntax implements Serializable, Cloneable {
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private static final long serialVersionUID = -2739521845085831642L;
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/**
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* This enumeration value's integer value.
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* @serial
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*/
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private int value;
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/**
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* Construct a new enumeration value with the given integer value.
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*
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* @param value Integer value.
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*/
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protected EnumSyntax(int value) {
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this.value = value;
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}
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/**
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* Returns this enumeration value's integer value.
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* @return the value
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*/
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public int getValue() {
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return value;
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}
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/**
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* Returns a clone of this enumeration value, which to preserve the
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* semantics of enumeration values is the same object as this enumeration
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* value.
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*/
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public Object clone() {
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return this;
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}
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/**
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* Returns a hash code value for this enumeration value. The hash code is
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* just this enumeration value's integer value.
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*/
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public int hashCode() {
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return value;
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}
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/**
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* Returns a string value corresponding to this enumeration value.
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*/
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public String toString() {
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String[] theTable = getStringTable();
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int theIndex = value - getOffset();
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return
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theTable != null && theIndex >= 0 && theIndex < theTable.length ?
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theTable[theIndex] :
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Integer.toString (value);
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}
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/**
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* During object input, convert this deserialized enumeration instance to
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* the proper enumeration value defined in the enumeration attribute class.
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*
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* @return The enumeration singleton value stored at index
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* <I>i</I>-<I>L</I> in the enumeration value table returned by
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* {@link #getEnumValueTable() getEnumValueTable()},
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* where <I>i</I> is this enumeration value's integer value and
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* <I>L</I> is the value returned by {@link #getOffset()
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* getOffset()}.
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*
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* @throws ObjectStreamException if the stream can't be deserialised
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* @throws InvalidObjectException
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* Thrown if the enumeration value table is null, this enumeration
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* value's integer value does not correspond to an element in the
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* enumeration value table, or the corresponding element in the
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* enumeration value table is null. (Note: {@link
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* java.io.InvalidObjectException InvalidObjectException} is a subclass
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* of {@link java.io.ObjectStreamException ObjectStreamException}, which
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* <CODE>readResolve()</CODE> is declared to throw.)
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*/
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protected Object readResolve() throws ObjectStreamException {
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EnumSyntax[] theTable = getEnumValueTable();
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if (theTable == null) {
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throw new InvalidObjectException(
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"Null enumeration value table for class " +
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getClass());
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}
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int theOffset = getOffset();
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int theIndex = value - theOffset;
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if (0 > theIndex || theIndex >= theTable.length) {
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throw new InvalidObjectException
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("Integer value = " + value + " not in valid range " +
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theOffset + ".." + (theOffset + theTable.length - 1) +
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"for class " + getClass());
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}
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EnumSyntax result = theTable[theIndex];
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if (result == null) {
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throw new InvalidObjectException
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("No enumeration value for integer value = " +
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value + "for class " + getClass());
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}
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return result;
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}
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// Hidden operations to be implemented in a subclass.
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/**
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* Returns the string table for this enumeration value's enumeration class.
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* The enumeration class's integer values are assumed to lie in the range
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* <I>L</I>..<I>L</I>+<I>N</I>-1, where <I>L</I> is the value returned by
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* {@link #getOffset() getOffset()} and <I>N</I> is the length
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* of the string table. The element in the string table at index
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* <I>i</I>-<I>L</I> is the value returned by {@link #toString()
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* toString()} for the enumeration value whose integer value
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* is <I>i</I>. If an integer within the above range is not used by any
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* enumeration value, leave the corresponding table element null.
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* <P>
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* The default implementation returns null. If the enumeration class (a
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* subclass of class EnumSyntax) does not override this method to return a
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* non-null string table, and the subclass does not override the {@link
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* #toString() toString()} method, the base class {@link
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* #toString() toString()} method will return just a string
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* representation of this enumeration value's integer value.
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* @return the string table
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*/
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protected String[] getStringTable() {
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return null;
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}
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/**
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* Returns the enumeration value table for this enumeration value's
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* enumeration class. The enumeration class's integer values are assumed to
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* lie in the range <I>L</I>..<I>L</I>+<I>N</I>-1, where <I>L</I> is the
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* value returned by {@link #getOffset() getOffset()} and
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* <I>N</I> is the length of the enumeration value table. The element in the
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* enumeration value table at index <I>i</I>-<I>L</I> is the enumeration
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* value object whose integer value is <I>i</I>; the {@link #readResolve()
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* readResolve()} method needs this to preserve singleton
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* semantics during deserialization of an enumeration instance. If an
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* integer within the above range is not used by any enumeration value,
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* leave the corresponding table element null.
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* <P>
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* The default implementation returns null. If the enumeration class (a
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* subclass of class EnumSyntax) does not override this method to return
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* a non-null enumeration value table, and the subclass does not override
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* the {@link #readResolve() readResolve()} method, the base
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* class {@link #readResolve() readResolve()} method will throw
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* an exception whenever an enumeration instance is deserialized from an
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* object input stream.
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* @return the value table
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*/
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protected EnumSyntax[] getEnumValueTable() {
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return null;
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}
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/**
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* Returns the lowest integer value used by this enumeration value's
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* enumeration class.
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* <P>
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* The default implementation returns 0. If the enumeration class (a
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* subclass of class EnumSyntax) uses integer values starting at other than
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* 0, override this method in the subclass.
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* @return the offset of the lowest enumeration value.
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*/
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protected int getOffset() {
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return 0;
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}
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}
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