Java Reference
In-Depth Information
9
System.out.println(
"All books:"
);
10
11
// print all books in enum Book
12
for
(
Book book : Book.values()
)
13
System.out.printf(
"%-10s%-45s%s%n"
, book,
14
book.getTitle() book.getCopyrightYear()
,
);
15
16
System.out.printf(
"%nDisplay a range of enum constants:%n"
);
17
18
// print first four books
19
for
(Book book :
EnumSet.range(Book.JHTP, Book.CPPHTP)
)
20
System.out.printf(
"%-10s%-45s%s%n"
, book,
21
book.getTitle() book.getCopyrightYear()
,
);
22
}
23
}
// end class EnumTest
All books:
JHTP Java How to Program 2015
CHTP C How to Program 2013
IW3HTP Internet & World Wide Web How to Program 2012
CPPHTP C++ How to Program 2014
VBHTP Visual Basic How to Program 2014
CSHARPHTP Visual C# How to Program 2014
Display a range of enum constants:
JHTP Java How to Program 2015
CHTP C How to Program 2013
IW3HTP Internet & World Wide Web How to Program 2012
CPPHTP C++ How to Program 2014
Fig. 8.11
|
Testing
enum
type
Book
. (Part 2 of 2.)
Lines 19-21 use the
static
method
range
of class
EnumSet
(declared in package
java.util
) to display a range of the
enum
Book
's constants. Method
range
takes two
parameters—the first and the last
enum
constants in the range—and returns an
EnumSet
that contains all the constants between these two constants, inclusive. For example, the
expression
EnumSet.range(Book.JHTP
,
Book.CPPHTP)
returns an
EnumSet
containing
Book.JHTP
,
Book.CHTP
,
Book.IW3HTP
and
Book.CPPHTP
. The enhanced
for
statement can
be used with an
EnumSet
just as it can with an array, so lines 12-14 use it to display the
title and copyright year of every book in the
EnumSet
. Class
EnumSet
provides several other
static
methods for creating sets of
enum
constants from the same
enum
type.
Common Programming Error 8.4
In an
enum
declaration, it's a syntax error to declare
enum
constants after the
enum
type's
constructors, fields and methods.
Every object uses system resources, such as memory. We need a disciplined way to give
resources back to the system when they're no longer needed; otherwise, “resource leaks”
might occur that would prevent resources from being reused by your program or possibly
