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
instance 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 syntax that consists of nonnegative 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 specification is described by the following formal grammar:
- SpecificationVersion:
- Digits RefinedVersionopt
- RefinedVersion:
.
Digits.
Digits RefinedVersion- Digits:
- Digit
- Digits
- Digit:
- any character for which
Character.isDigit(char)
returnstrue
, e.g. 0, 1, 2, ...
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 identifiers.
Within each ClassLoader
instance 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.
Public Method Summary
<A extends Annotation> A |
getAnnotation(Class<A> annotationClass)
|
Annotation[] |
getAnnotations()
Returns annotations that are present on this element.
|
<A extends Annotation> A[] |
getAnnotationsByType(Class<A> annotationClass)
|
<A extends Annotation> A |
getDeclaredAnnotation(Class<A> annotationClass)
|
Annotation[] |
getDeclaredAnnotations()
Returns annotations that are directly present on this element.
|
<A extends Annotation> A[] |
getDeclaredAnnotationsByType(Class<A> annotationClass)
|
String |
getImplementationTitle()
Return the title of this package.
|
String |
getImplementationVendor()
Returns the name of the organization,
vendor or company that provided this implementation.
|
String |
getImplementationVersion()
Return the version of this implementation.
|
String |
getName()
Return the name of this package.
|
static Package | |
static Package[] |
getPackages()
Get all the packages currently known for the caller's
ClassLoader
instance. |
String |
getSpecificationTitle()
Return the title of the specification that this package implements.
|
String |
getSpecificationVendor()
Return the name of the organization, vendor,
or company that owns and maintains the specification
of the classes that implement this package.
|
String |
getSpecificationVersion()
Returns the version number of the specification
that this package implements.
|
int |
hashCode()
Return the hash code computed from the package name.
|
boolean |
isAnnotationPresent(Class<? extends Annotation> annotationClass)
Returns true if an annotation for the specified type
is present on this element, else false.
|
boolean |
isCompatibleWith(String desired)
Compare this package's specification version with a
desired version.
|
boolean | |
boolean |
isSealed()
Returns true if this package is sealed.
|
String |
toString()
Returns the string representation of this Package.
|
Inherited Method Summary
Public Methods
public A getAnnotation (Class<A> annotationClass)
public Annotation[] getAnnotations ()
Returns annotations that are present on this element. If there are no annotations present on this element, the return value is an array of length 0. The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.
Returns
- annotations present on this element
public A[] getAnnotationsByType (Class<A> annotationClass)
public A getDeclaredAnnotation (Class<A> annotationClass)
public Annotation[] getDeclaredAnnotations ()
Returns annotations that are directly present on this element. This method ignores inherited annotations. If there are no annotations directly present on this element, the return value is an array of length 0. The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.
Returns
- annotations directly present on this element
public A[] getDeclaredAnnotationsByType (Class<A> annotationClass)
public String getImplementationTitle ()
Return the title of this package.
Returns
- the title of the implementation, null is returned if it is not known.
public String getImplementationVendor ()
Returns the name of the organization, vendor or company that provided this implementation.
Returns
- the vendor that implemented this package..
public String getImplementationVersion ()
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.
public String getName ()
Return the name of this package.
Returns
- The fully-qualified name of this package as defined in section 6.5.3 of
The Java™ Language Specification,
for example,
java.lang
public static Package getPackage (String packageName)
Find a package by name in the callers ClassLoader
instance.
The callers ClassLoader
instance is used to find the package
instance corresponding to the named class. If the callers
ClassLoader
instance is null then the set of packages loaded
by the system ClassLoader
instance 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
packageName |
---|
Returns
- the package of the requested name. It may be null if no package information is available from the archive or codebase.
public static Package[] getPackages ()
Get all the packages currently known for the caller's ClassLoader
instance. Those packages correspond to classes loaded via or accessible by
name to that ClassLoader
instance. If the caller's
ClassLoader
instance is the bootstrap ClassLoader
instance, which may be represented by null
in some implementations,
only packages corresponding to classes loaded by the bootstrap
ClassLoader
instance will be returned.
Returns
- a new array of packages known to the callers
ClassLoader
instance. An zero length array is returned if none are known.
public String getSpecificationTitle ()
Return the title of the specification that this package implements.
Returns
- the specification title, null is returned if it is not known.
public String 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 specification vendor, null is returned if it is not known.
public String getSpecificationVersion ()
Returns the version number of the specification that this package implements. This version string must be a sequence of nonnegative 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.
public int hashCode ()
Return the hash code computed from the package name.
Returns
- the hash code computed from the package name.
public boolean isAnnotationPresent (Class<? extends Annotation> annotationClass)
Returns true if an annotation for the specified type is present on this element, else false. This method is designed primarily for convenient access to marker annotations.
The truth value returned by this method is equivalent to:
getAnnotation(annotationClass) != null
The body of the default method is specified to be the code above.
Parameters
annotationClass | the Class object corresponding to the annotation type |
---|
Returns
- true if an annotation for the specified annotation type is present on this element, else false
Throws
NullPointerException |
---|
public boolean isCompatibleWith (String desired)
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. |
---|
public boolean isSealed (URL url)
Returns true if this package is sealed with respect to the specified code source url.
Parameters
url | the code source url |
---|
Returns
- true if this package is sealed with respect to url
public boolean isSealed ()
Returns true if this package is sealed.
Returns
- true if the package is sealed, false otherwise
public String toString ()
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.
Returns
- the string representation of the package.