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:
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
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 getValue().
An enumeration value's integer value is established when it is constructed
(see 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.
| Modifier and Type | Field and Description |
|---|---|
| private static final long | serialVersionUID
Use serialVersionUID from JDK 1.4 for interoperability. |
| private int | value
This enumeration value's integer value. |
| Access | Constructor and Description |
|---|---|
| protected |
| Modifier and Type | Method and Description |
|---|---|
| public Object | clone()
Overrides java. |
| protected EnumSyntax[] | Returns: the value tableReturns the enumeration value table for this enumeration value's enumeration class. |
| protected int | Returns: the offset of the lowest enumeration valueReturns the lowest integer value used by this enumeration value's enumeration class. |
| protected String[] | Returns: the string tableReturns the string table for this enumeration value's enumeration class. |
| public int | |
| public int | hashCode()
Overrides java. |
| protected Object | Returns: The enumeration singleton value stored at index i-L in the enumeration value table returned bygetEnumValueTable(), where i
is this enumeration value's integer value and L is the
value returned by getOffset()During object input, convert this deserialized enumeration instance to the proper enumeration value defined in the enumeration attribute class. |
| public String | toString()
Overrides java. |
| serialVersionUID | back to summary |
|---|---|
| private static final long serialVersionUID Use serialVersionUID from JDK 1.4 for interoperability. | |
| value | back to summary |
|---|---|
| private int value This enumeration value's integer value. | |
| EnumSyntax | back to summary |
|---|---|
| protected EnumSyntax(int value) Construct a new enumeration value with the given integer value.
| |
| clone | back to summary |
|---|---|
| public Object clone() Overrides java. Returns a clone of this enumeration value, which to preserve the semantics of enumeration values is the same object as this enumeration value.
| |
| getEnumValueTable | back to summary |
|---|---|
| protected EnumSyntax[] getEnumValueTable() 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
The default implementation returns
| |
| getOffset | back to summary |
|---|---|
| protected int getOffset() 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
| |
| getStringTable | back to summary |
|---|---|
| protected String[] getStringTable() 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
The default implementation returns
| |
| getValue | back to summary |
|---|---|
| public int getValue() Returns this enumeration value's integer value.
| |
| hashCode | back to summary |
|---|---|
| public int hashCode() Overrides java. Returns a hash code value for this enumeration value. The hash code is just this enumeration value's integer value.
| |
| readResolve | back to summary |
|---|---|
| protected Object readResolve() throws ObjectStreamException During object input, convert this deserialized enumeration instance to the proper enumeration value defined in the enumeration attribute class.
| |
| toString | back to summary |
|---|---|
| public String toString() Overrides java. Returns a string value corresponding to this enumeration value.
| |