Package (Java Platform SE 8 )
Keywords: java.lang.Package class
Date: 2015-11-18

compact1, compact2, compact3
java.lang

## Class Package

- java.lang.Object
- - java.lang.Package

- All Implemented Interfaces:
    AnnotatedElement

      public class Package
      extends Object
      implements AnnotatedElement

  `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)` 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.

  See Also:
    `ClassLoader.definePackage(java.lang.String, java.lang.String, java.lang.String, java.lang.String, java.lang.String, java.lang.String, java.lang.String, java.net.URL)`

- - ### Method Summary

    All Methods Static Methods Instance Methods Concrete Methods
    Modifier and Type | Method and Description
    --- | ---
    `<A extends Annotation> A` | `getAnnotation(Class<A> annotationClass)` Returns this element's annotation for the specified type if such an annotation is present, else null.
    `Annotation[]` | `getAnnotations()` Returns annotations that are present on this element.
    `<A extends Annotation> A[]` | `getAnnotationsByType(Class<A> annotationClass)` Returns annotations that are associated with this element.
    `<A extends Annotation> A` | `getDeclaredAnnotation(Class<A> 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.
    `<A extends Annotation> A[]` | `getDeclaredAnnotationsByType(Class<A> 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 name)` 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()` Returns true if this package is sealed.
    `boolean` | `isSealed(URL url)` Returns true if this package is sealed with respect to the specified code source url.
    `String` | `toString()` Returns the string representation of this Package.

    - ### Methods inherited from class java.lang.Object

      `clone, equals, finalize, getClass, notify, notifyAll, wait, wait, wait`

- - ### Method Detail

    - #### getName

          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`

    - #### getSpecificationTitle

          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.

    - #### getSpecificationVersion

          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.

    - #### 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.
      Returns:
        the specification vendor, null is returned if it is not known.

    - #### getImplementationTitle

          public String getImplementationTitle()

      Return the title of this package.
      Returns:
        the title of the implementation, null is returned if it is not known.

    - #### 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.
      Returns:
        the version of the implementation, null is returned if it is not known.

    - #### getImplementationVendor

          public String getImplementationVendor()

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

    - #### isSealed

          public boolean isSealed()

      Returns true if this package is sealed.
      Returns:
        true if the package is sealed, false otherwise

    - #### isSealed

          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

    - #### 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.

      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.

    - #### 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.

      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.

    - #### 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.
      Returns:
        a new array of packages known to the callers `ClassLoader` instance. An zero length array is returned if none are known.

    - #### hashCode

          public int hashCode()

      Return the hash code computed from the package name.
      Overrides:
        `hashCode` in class `Object`
      Returns:
        the hash code computed from the package name.
      See Also:
        `Object.equals(java.lang.Object)`, `System.identityHashCode(java.lang.Object)`

    - #### 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.
      Overrides:
        `toString` in class `Object`
      Returns:
        the string representation of the package.

    - #### getAnnotation

          public <A extends Annotation> A getAnnotation(Class<A> annotationClass)

      Description copied from interface: `AnnotatedElement`
      Returns this element's annotation for the specified type if such an annotation is present, else null.
      Specified by:
        `getAnnotation` in interface `AnnotatedElement`
      Type Parameters:
        `A` - the type of the annotation to query for and return if present
      Parameters:
        `annotationClass` - the Class object corresponding to the annotation type
      Returns:
        this element's annotation for the specified annotation type if present on this element, else null
      Throws:
        `NullPointerException` - if the given annotation class is null
      Since:
        1.5

    - #### isAnnotationPresent

          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.

      Specified by:
        `isAnnotationPresent` in interface `AnnotatedElement`
      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` - if the given annotation class is null
      Since:
        1.5

    - #### getAnnotationsByType

          public <A extends Annotation> A[] getAnnotationsByType(Class<A> annotationClass)

      Description copied from interface: `AnnotatedElement`
      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 `AnnotatedElement.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.
      Specified by:
        `getAnnotationsByType` in interface `AnnotatedElement`
      Type Parameters:
        `A` - the type of the annotation to query for and return if present
      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
      Throws:
        `NullPointerException` - if the given annotation class is null
      Since:
        1.8

    - #### getAnnotations

          public Annotation[] getAnnotations()

      Description copied from interface: `AnnotatedElement`
      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.
      Specified by:
        `getAnnotations` in interface `AnnotatedElement`
      Returns:
        annotations present on this element
      Since:
        1.5

    - #### getDeclaredAnnotation

          public <A extends Annotation> A getDeclaredAnnotation(Class<A> annotationClass)

      Description copied from interface: `AnnotatedElement`
      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.)
      Specified by:
        `getDeclaredAnnotation` in interface `AnnotatedElement`
      Type Parameters:
        `A` - the type of the annotation to query for and return if directly present
      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
      Throws:
        `NullPointerException` - if the given annotation class is null
      Since:
        1.8

    - #### getDeclaredAnnotationsByType

          public <A extends Annotation> A[] getDeclaredAnnotationsByType(Class<A> annotationClass)

      Description copied from interface: `AnnotatedElement`
      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 `AnnotatedElement.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.
      Specified by:
        `getDeclaredAnnotationsByType` in interface `AnnotatedElement`
      Type Parameters:
        `A` - the type of the annotation to query for and return if directly or indirectly present
      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
      Throws:
        `NullPointerException` - if the given annotation class is null
      Since:
        1.8

    - #### getDeclaredAnnotations

          public Annotation[] getDeclaredAnnotations()

      Description copied from interface: `AnnotatedElement`
      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.
      Specified by:
        `getDeclaredAnnotations` in interface `AnnotatedElement`
      Returns:
        annotations directly present on this element
      Since:
        1.5

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