Java Reference
In-Depth Information
System.out.println("Sealed: "+pkg.isSealed());
if (args.length > 1)
System.out.println("Compatible with "+args[1]+":
After compiling Listing 4-3 ( javac ), specify at least a
packagenameonthecommandlinewhenyourunthisapplication.Forexample, java
PackageInfo java.lang returns the following output under Java 7:
Name: java.lang
Implementation title: Java Runtime Environment
Implementation vendor: Oracle Corporation
Implementation version: 1.7.0
Specification title: Java Platform API Specification
Specification vendor: Oracle Corporation
Specification version: 1.7
Sealed: false
PackageInfo also lets you determine if the package's specification is compatible
with a specific version number. A package is compatible with its predecessors.
For example, java PackageInfo java.lang 1.7 outputs Compatible
with 1.7: true , whereas java PackageInfo java.lang 1.8 outputs
Compatible with 1.8: false .
Youcanalsouse PackageInfo withyourownpackages,whichyoulearnedtocre-
ate in Chapter 3 . For example, that chapter presented a logging package.
Copy PackageInfo.class intothedirectorycontainingthe logging package
directory(whichcontainsthecompiledclassfiles),andexecute java PackageInfo
logging .
PackageInfo responds by displaying the following output:
logging not found
This error message is presented because getPackage() requires at least one
classfiletobeloadedfromthepackagebeforeitreturnsa Package objectdescribing
that package.
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