Java The Complete Reference, Seventh Edition

Enum

As described in Chapter 12, enumerations were recently added to the Java language. (Recall that

an enumeration is created by using the keywordenum.) All enumerations automatically inherit

Enum.Enumis a generic class that is declared as shown here:

class Enum<E extends Enum<E>>

Here,Estands for the enumeration type.Enumhas no public constructors.

Enumdefines several methods that are available for use by all enumerations, which are

shown in Table 16-21.

432 Part II: The Java Library

Method Description

int getLineNumber( ) Returns the source-code line number of the execution point described

by the invokingStackTraceElement. In some situations, the line

number will not be available, in which case a negative value is

returned.

String getMethodName( ) Returns the method name of the execution point described by the

invokingStackTraceElement.

int hashCode( ) Returns the hash code for the invokingStackTraceElement.

boolean isNativeMethod( ) Returnstrueif the invokingStackTraceElementdescribes a native

method. Other wise, returnsfalse.

String toString( ) Returns theStringequivalent of the invoking sequence.

TABLE 16-20 The Methods Defined byStackTraceElement(continued)

Method Description

protected final Object clone( )

throws CloneNotSupportedException

Invoking this method causes a

CloneNotSupportedExceptionto be thrown. This

prevents enumerations from being cloned.

final int compareTo(Ee) Compares the ordinal value of two constants of the

same enumeration. Returns a negative value if the

invoking constant has an ordinal value less thane’s,

zero if the two ordinal values are the same, and a

positive value if the invoking constant has an ordinal

value greater thane’s.

final boolean equals(Objectobj) Returns true ifobjand the invoking object refer

to the same constant.

final Class<E> getDeclaringClass( ) Returns the type of enumeration of which the

invoking constant is a member.

final int hashCode( ) Returns the hash code for the invoking object.

TABLE 16-21 The Methods Defined byEnum