Documentation  › java.lang  › Package
 
 


  Package
  public

  Inherits From:   Object
  Conforms To:   none
  Declared In:   java.lang


Class Description
 
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 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 specification is described by the following formal grammar:

SpecificationVersion:
Digits RefinedVersionopt

RefinedVersion:
. Digits
. Digits RefinedVersion

Digits:
Digit
Digits

Digit:
any character for which isDigit 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 identifers.

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.



Class Variables
 
None declared in this class.


Instance Variables
 
None declared in this class.


Constructors
 
None declared in this class.


Class Methods
 
getPackage
public static Package getPackage( String name )

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.


getPackages
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.



Instance Methods
 
getImplementationTitle
public String getImplementationTitle( )

Return the title of this package.


getImplementationVendor
public String getImplementationVendor( )

Returns the name of the organization, vendor or company that provided this implementation.


getImplementationVersion
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.


getName
public String getName( )

Return the name of this package.


getSpecificationTitle
public String getSpecificationTitle( )

Return the title of the specification that this package implements.


getSpecificationVendor
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.


getSpecificationVersion
public String getSpecificationVersion( )

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.


hashCode
public int hashCode( )

Return the hash code computed from the package name.


isCompatibleWith
public boolean isCompatibleWith( String desired ) throws NumberFormatException

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.


isSealed
public boolean isSealed( )

Returns true if this package is sealed.


isSealed
public boolean isSealed( URL url )

Returns true if this package is sealed with respect to the specified code source url.


toString
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.



Known Subclasses
 
None.



 
 
  dydoc
  3/10/05