Java Reference
In-Depth Information
Note ReversedInternetdomainnamesarenotalwaysvalidpackagenames.Oneor
moreofitscomponentnamesmightstartwithadigit( ),containahyphen( - )or
other illegal character ( ), or be one of Java's reserved words ( ).
Conventiondictatesthatyouprefixthedigitwithanunderscore( com._6 ),replacethe
illegal character with an underscore ( com.aq_x ), and suffix the reserved word with
an underscore ( com.int_ ).
The Package Statement
This statement consists of reserved word package , followed by a member access
operator-separated list of package and subpackage names, followed by a semicolon.
Forexample, package graphics; specifiesthatthesourcefile'stypeslocateina
packagenamed graphics ,and package graphics.shapes; specifiesthatthe
source file's types locate in the graphics package's shapes subpackage.
By convention, a package name is expressed in lowercase. If the name consists of
multiple words, each word except for the first word is capitalized.
Onlyonepackage statement canappear inasourcefile. Whenitispresent, nothing
apart from comments must precede this statement.
Caution Specifyingmultiplepackagestatementsinasourcefileorplacinganything
Java implementations map package and subpackage names to same-named direct-
ories. For example, an implementation would map graphics to a directory named
graphics , and would map graphics.shapes to a shapes subdirectory of
graphics .TheJavacompilerstorestheclassfilesthatimplementthepackage'stypes
in the corresponding directory.
Note Ifasourcefiledoesnotcontainapackagestatement,thesourcefile'stypesare
saidtobelongtothe unnamed package .Thispackagecorrespondstothecurrentdirect-
The Import Statement
Imagine having to repeatedly specify or some other lengthy package-
qualified type name for each occurrence of that type in source code. Java provides an
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