7.1

Package Members

PACKAGES

For small programs and casual development, a package can be unnamed

( 7.4.2) or have a simple name, but if Java code is to be widely distributed, unique

package names should be chosen ( 7.7). This can prevent the conflicts that would

otherwise occur if two development groups happened to pick the same package

name and these packages were later to be used in a single program.

7.1   Package Members

A

 package

 can have members of either or both of the following kinds:

Subpackages of the package

Types declared in the compilation units ( 7.3) of the package

For example, in the standard Java Application Programming Interface:

The package

java

 has subpackages

awt

,

applet

,

io

,

lang

,

net

, and

util

,

but no compilation units.

The package

java.awt

 has a subpackage named

image

, as well as a number

of compilation units containing declarations of class and interface types.

If the fully qualified name ( 6.7) of a package is

P

, and

Q

 is a subpackage of

P

,

then

P.Q

 is the fully qualified name of the subpackage.

The subpackages of package

java

 named

lang

,

util

, and

io

 (whose fully

qualified package names are therefore

java.lang

,

java.util

, and

java.io

) are

a standard part of every Java implementation and are specified in Chapters 20, 21,

and 22. Many Java implementations will include the entire set of

java

 packages

defined in the series of books

The Java Application Programming Interface

.

A package may not contain a type declaration and a subpackage of the same

name, or a compile time error results. Here are some examples:

Because the package

java.awt

 has a subpackage

image

, it cannot (and does

not) contain a declaration of a class or interface type named

image

.

If there is a package named

mouse

 and a type

Button

 in that package (which

then might be referred to as

mouse.Button

), then there cannot be any pack 

age with the fully qualified name

mouse.Button

 or

mouse.Button.Click

.

If

COM.Sun.java.jag

 is the fully qualified name of a type, then there cannot

be any package whose fully qualified name is either

COM.Sun.java.jag

 or

COM.Sun.java.jag.scrabble

.

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