Package - JRE Emulation | JRE Emulation
public class

Package

extends Object
implements AnnotatedElement
java.lang.Object
   ↳ java.lang.Package

Class Overview

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 isDigit(char) returns true, 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.

Summary

Public Methods
<A extends Annotation> A getAnnotation(Class<A> annotationClass)
Annotation[] getAnnotations()
Returns annotations that are present on this element.
<T extends Annotation> T[] getAnnotationsByType(Class<T> annotationClass)
Returns annotations that are associated with this element.
<T extends Annotation> T getDeclaredAnnotation(Class<T> annotationClass)
Returns this element's annotation for the specified type if such an annotation is directly present, else null.
Annotation[] getDeclaredAnnotations()
Returns annotations that are directly present on this element.
<T extends Annotation> T[] getDeclaredAnnotationsByType(Class<T> annotationClass)
Returns this element's annotation(s) for the specified type if such annotations are either directly present or indirectly present.
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 getPackage(String packageName)
Find a package by name in the callers ClassLoader instance.
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 isSealed(URL url)
Returns true if this package is sealed with respect to the specified code source url.
boolean isSealed()
Returns true if this package is sealed.
String toString()
Returns the string representation of this Package.
Inherited Methods
[Expand]
From class java.lang.Object
From interface java.lang.reflect.AnnotatedElement

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 T[] getAnnotationsByType (Class<T> annotationClass)

Returns annotations that are associated with this element. If there are no annotations associated with this element, the return value is an array of length 0. The difference between this method and getAnnotation(Class) is that this method detects if its argument is a repeatable annotation type (JLS 9.6), and if so, attempts to find one or more annotations of that type by "looking through" a container annotation. The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.

Parameters
annotationClass the Class object corresponding to the annotation type
Returns
  • all this element's annotations for the specified annotation type if associated with this element, else an array of length zero

public T getDeclaredAnnotation (Class<T> annotationClass)

Returns this element's annotation for the specified type if such an annotation is directly present, else null. This method ignores inherited annotations. (Returns null if no annotations are directly present on this element.)

Parameters
annotationClass the Class object corresponding to the annotation type
Returns
  • this element's annotation for the specified annotation type if directly present on this element, else null

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 T[] getDeclaredAnnotationsByType (Class<T> annotationClass)

Returns this element's annotation(s) for the specified type if such annotations are either directly present or indirectly present. This method ignores inherited annotations. If there are no specified annotations directly or indirectly present on this element, the return value is an array of length 0. The difference between this method and getDeclaredAnnotation(Class) is that this method detects if its argument is a repeatable annotation type (JLS 9.6), and if so, attempts to find one or more annotations of that type by "looking through" a container annotation if one is present. The caller of this method is free to modify the returned array; it will have no effect on the arrays returned to other callers.

Parameters
annotationClass the Class object corresponding to the annotation type
Returns
  • all this element's annotations for the specified annotation type if directly or indirectly present on this element, else an array of length zero

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.

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

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.