* 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;
* }
* }
*
* You can then write code that uses the == and !=
* operators to test enumeration values; for example:
*
* Bach theComposer;
* . . .
* if (theComposer == Bach.JOHANN_SEBASTIAN) {
* System.out.println ("The greatest composer of all time!");
* }
*
* The equals() method for an enumeration class just does a test
* for identical objects (==).
* * You can convert an enumeration value to a string by calling {@link * #toString() toString()}. The string is obtained from a table * supplied by the enumeration class. *
* 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() * getValue()}. An enumeration value's integer value is established * when it is constructed (see {@link #EnumSyntax(int) * EnumSyntax(int)}). 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. *
* 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 ==, !=, equals(), and
* toString() 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.
*
* @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-L in the enumeration value table returned by
* {@link #getEnumValueTable() getEnumValueTable()},
* where i is this enumeration value's integer value and
* L is the value returned by {@link #getOffset()
* getOffset()}.
*
* @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
* readResolve() 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
* L..L+N-1, where L is the value returned by
* {@link #getOffset() getOffset()} and N is the length
* of the string table. The element in the string table at index
* i-L is the value returned by {@link #toString()
* toString()} for the enumeration value whose integer value
* is i. If an integer within the above range is not used by any
* enumeration value, leave the corresponding table element null.
*
* 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() toString()} method, the base class {@link * #toString() toString()} 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 L..L+N-1, where L is the * value returned by {@link #getOffset() getOffset()} and * N is the length of the enumeration value table. The element in the * enumeration value table at index i-L is the enumeration * value object whose integer value is i; the {@link #readResolve() * readResolve()} 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. *
* 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() readResolve()} method, the base * class {@link #readResolve() readResolve()} 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. *
* 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; } }