Package objects contain version information
about the implementation and specification of a Java package.
This versioning information is retrieved and made available
by the classloader that loaded the class(es). Typically, it is
stored in the manifest that is distributed with the classes.
The set of classes that make up the package may implement a
particular specification and if
so the specification title, version number, and vendor strings
identify that specification.
An application can ask if the package is
compatible with a particular version, see the isCompatibleWith
method for details.
Specification version numbers use a "Dewey Decimal"
syntax that consists of positive decimal integers
separated by periods ".", for example, "2.0" or "1.2.3.4.5.6.7".
This allows an extensible number to be used to
represent major, minor, micro, etc versions.
The version number must begin with a number.
The implementation title, version, and vendor strings identify an
implementation and are made available conveniently to enable accurate
reporting of the packages involved when a problem occurs. The contents
all three implementation strings are vendor specific. The
implementation version strings have no specified syntax and should
only be compared for equality with desired version identifers.
Within each classloader all classes from the same java package have
the same Package object. The static methods allow a package
to be found by name or the set of all packages known
to the current class loader to be found.
getSpecificationVendor()
Return the name of the organization, vendor,
or company that owns and maintains the specification
of the classes that implement this package.
Returns the version number of the specification
that this package implements.
This version string must be a sequence of positive decimal
integers separated by "."'s and may have leading zeros.
When version strings are compared the most significant
numbers are compared.
Returns:
the specification version, null is returned if it is not known.
Return the version of this implementation. It consists of any string
assigned by the vendor of this implementation and does
not have any particular syntax specified or expected by the Java
runtime. It may be compared for equality with other
package version strings used for this implementation
by this vendor for this package.
Returns:
the version of the implementation, null is returned if it is not known.
Compare this package's specification version with a
desired version. It returns true if
this packages specification version number is greater than or equal
to the desired version number.
Version numbers are compared by sequentially comparing corresponding
components of the desired and specification strings.
Each component is converted as a decimal integer and the values
compared.
If the specification value is greater than the desired
value true is returned. If the value is less false is returned.
If the values are equal the period is skipped and the next pair of
components is compared.
Parameters:
desired - the version string of the desired version.
Returns:
true if this package's version number is greater
than or equal to the desired version number
Throws:
NumberFormatException - if the desired or current version
is not of the correct dotted form.
Find a package by name in the callers classloader.
The callers classloader is used to find the package instance
corresponding to the named class. If the callers classloader
is null then the set of packages loaded by the system
classloader is searched to find the named package.
Packages have attributes for versions and specifications only
if the class loader created the package
instance with the appropriate attributes. Typically, those
attributes are defined in the manifests that accompany
the classes.
Parameters:
name - a package name, for example, java.lang.
Returns:
the package of the requested name. It may be null if no package
information is available from the archive or codebase.
Get all the packages currently known for the caller's class loader.
Those packages correspond to classes loaded via or accessible
by name to that class loader. If the caller's class loader is
the bootstrap classloader, which may be represented by
null in some implementations, only packages corresponding
to classes loaded by the bootstrap class loader will be returned.
Returns:
a new array of packages known to the callers classloader.
An zero length array is returned if none are known.
hashCode
public int hashCode()
Return the hashcode computed from the package name.
Returns the string representation of this Package.
Its value is the string "package " and the package name.
If the package title is defined it is appended.
If the package version is defined it is appended.
Submit a bug or feature For further API reference and developer documentation, see Java 2 SDK SE Developer Documentation. That documentation contains more detailed, developer-targeted descriptions, with conceptual overviews, definitions of terms, workarounds, and working code examples.
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