Module java.base
Package java.lang

Class Package

  • All Implemented Interfaces:
    AnnotatedElement
    public classPackageextendsObjectimplementsAnnotatedElement
    Represents metadata about a run-time package associated with a class loader. Metadata includes annotations, versioning, and sealing.

    Annotations for the run-time package are read frompackage-info.class at the same code source as classes in the run-time package.

    The set of classes that make up the run-time package may implement a particular specification. The specification title, version, and vendor (indicating the owner/maintainer of the specification) can be provided when thePackage is defined. An application can ask if thePackage is compatible with a particular specification version by using thePackage.isCompatibleWith(String) method. In addition, information about the actual classes that make up the run-time package can be provided when the Package is defined. This information consists of an implementation title, version, and vendor (indicating the supplier of the classes).

    APackage may be explicitly defined with theClassLoader.definePackage(String, String, String, String, String, String, String, URL) method. The caller supplies the specification and implementation titles, versions, and vendors. The caller also indicates whether the package issealed. If aPackage is not explicitly defined for a run-time package when a class in that run-time package is defined, then aPackage is automatically defined by the class's defining class loader, as follows.

    APackage automatically defined for classes in a named module has the following properties:

    • The name of the package is derived from thebinary names of the classes. Since classes in a named module must be in a named package, the derived name is never empty.
    • The package is sealed with themodule location as the code source, if known.
    • The specification and implementation titles, versions, and vendors are unspecified.
    • Any annotations on the package are read frompackage-info.class as specified above.

    APackage automatically defined for classes in an unnamed module has the following properties:

    • The name of the package is either"" (for classes in an unnamed package) or derived from thebinary names of the classes (for classes in a named package).
    • The package is not sealed.
    • The specification and implementation titles, versions, and vendors are unspecified.
    • Any annotations on the package are read frompackage-info.class as specified above.

    APackage can be obtained with thePackage.getPackage(String) andClassLoader.getDefinedPackage(String) methods. EveryPackage defined by a class loader can be obtained with thePackage.getPackages() andClassLoader.getDefinedPackages() methods.

    Implementation Note:
    Thebuiltin class loaders do not explicitly definePackage objects for packages innamed modules. Instead those packages are automatically defined and have no specification and implementation versioning information.
    Since:
    1.2
    See Also:
    The JAR File Specification: Package Sealing,ClassLoader.definePackage(String, String, String, String, String, String, String, URL)
    SeeThe Java™ Virtual Machine Specification:
    5.3 Run-time package

    • 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 ofThe 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 non-negative decimal integers separated by "."'s and may have leading zeros. When version strings are compared the most significant numbers are compared.

        Specification version numbers use a syntax that consists of non-negative 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 whichCharacter.isDigit(char) returnstrue, e.g. 0, 1, 2, ...

        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 vendor that implemented this package,null is returned if it is not known.
        Returns:
        the vendor that implemented this package,null is returned if it is not known.

      • 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 sourceurl.
        Parameters:
        url - the code source URL
        Returns:
        true if this package is sealed with respect to the givenurl

      • isCompatibleWith

        public boolean isCompatibleWith​(String desired)                         throwsNumberFormatException
        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 current version is not known or the desired or current version is not of the correct dotted form.

      • getPackage

        @Deprecated(since="9")public static Package getPackage​(String name)
        Deprecated.
        If multiple class loaders delegate to each other and define classes with the same package name, and one such loader relies on the lookup behavior ofgetPackage to return aPackage from a parent loader, then the properties exposed by thePackage may not be as expected in the rest of the program. For example, thePackage will only expose annotations from thepackage-info.class file defined by the parent loader, even if annotations exist in apackage-info.class file defined by a child loader. A more robust approach is to use theClassLoader.getDefinedPackage(java.lang.String) method which returns aPackage for the specified class loader.
        Finds a package by name in the caller's class loader and its ancestors.

        If the caller's class loader defines aPackage of the given name, thePackage is returned. Otherwise, the ancestors of the caller's class loader are searched recursively (parent by parent) for aPackage of the given name.

        Calling this method is equivalent to callingClassLoader.getPackage(java.lang.String) on aClassLoader instance which is the caller's class loader.

        Parameters:
        name - A package name, such as "java.lang".
        Returns:
        ThePackage of the given name defined by the caller's class loader or its ancestors, ornull if not found.
        Throws:
        NullPointerException - ifname isnull.
        See Also:
        ClassLoader.getDefinedPackage(java.lang.String)

      • getPackages

        public static Package[] getPackages()
        Returns all of thePackages defined by the caller's class loader and its ancestors. The returned array may contain more than onePackage object of the same package name, each defined by a different class loader in the class loader hierarchy.

        Calling this method is equivalent to callingClassLoader.getPackages() on aClassLoader instance which is the caller's class loader.

        Returns:
        The array ofPackage objects defined by this class loader and its ancestors
        See Also:
        ClassLoader.getDefinedPackages()

      • 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 extendsAnnotation> A getAnnotation​(Class<A> annotationClass)
        Description copied from interface: AnnotatedElement
        Returns this element's annotation for the specified type if such an annotation ispresent, 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<? extendsAnnotation> annotationClass)
        Returns true if an annotation for the specified type ispresent 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 extendsAnnotation> A[] getAnnotationsByType​(Class<A> annotationClass)
        Description copied from interface: AnnotatedElement
        Returns annotations that areassociated with this element. If there are no annotationsassociated with this element, the return value is an array of length 0. The difference between this method andAnnotatedElement.getAnnotation(Class) is that this method detects if its argument is arepeatable 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 arepresent on this element. If there are no annotationspresent 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 extendsAnnotation> A getDeclaredAnnotation​(Class<A> annotationClass)
        Description copied from interface: AnnotatedElement
        Returns this element's annotation for the specified type if such an annotation isdirectly 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 extendsAnnotation> A[] getDeclaredAnnotationsByType​(Class<A> annotationClass)
        Description copied from interface: AnnotatedElement
        Returns this element's annotation(s) for the specified type if such annotations are eitherdirectly present orindirectly 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 andAnnotatedElement.getDeclaredAnnotation(Class) is that this method detects if its argument is arepeatable 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 aredirectly present on this element. This method ignores inherited annotations. If there are no annotationsdirectly 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