Class Module

All Implemented Interfaces:
AnnotatedElement
public final class Module
extends Object
implements AnnotatedElement

Represents a run-time module, either named or unnamed.

Named modules have a name and are constructed by the Java Virtual Machine when a graph of modules is defined to the Java virtual machine to create a module layer.

An unnamed module does not have a name. There is an unnamed module for each ClassLoader, obtained by invoking its getUnnamedModule method. All types that are not in a named module are members of their defining class loader's unnamed module.

The package names that are parameters or returned by methods defined in this class are the fully-qualified names of the packages as defined in section 6.5.3 of The Java™ Language Specification, for example, "java.lang".

Unless otherwise specified, passing a null argument to a method in this class causes a NullPointerException to be thrown.

Since:
9
See Also:
Class.getModule()

Methods

Modifier and Type Method Description
Module addExports​(String pn, Module other)

If the caller's module is this module then update this module to export the given package to the given module.
Module addOpens​(String pn, Module other)

If this module has opened a package to at least the caller module then update this module to open the package to the given module.
Module addReads​(Module other)

If the caller's module is this module then update this module to read the given module.
Module addUses​(Class<?> service)

If the caller's module is this module then update this module to add a service dependence on the given service type.
boolean canRead​(Module other)

Indicates if this module reads the given module.
boolean canUse​(Class<?> service)

Indicates if this module has a service dependence on the given service type.
<T extends Annotation>
T		 getAnnotation​(Class<T> 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.
ClassLoader getClassLoader()

Returns the ClassLoader for this module.
Annotation[] getDeclaredAnnotations()

Returns annotations that are directly present on this element.
ModuleDescriptor getDescriptor()

Returns the module descriptor for this module or null if this module is an unnamed module.
ModuleLayer getLayer()

Returns the module layer that contains this module or null if this module is not in a module layer.
String getName()

Returns the module name or null if this module is an unnamed module.
Set<String> getPackages()

Returns the set of package names for the packages in this module.
InputStream getResourceAsStream​(String name)

Returns an input stream for reading a resource in this module.
boolean isExported​(String pn)

Returns true if this module exports the given package unconditionally.
boolean isExported​(String pn, Module other)

Returns true if this module exports the given package to at least the given module.
boolean isNamed()

Returns true if this module is a named module.
boolean isOpen​(String pn)

Returns true if this module has opened a package unconditionally.
boolean isOpen​(String pn, Module other)

Returns true if this module has opened a package to at least the given module.
String toString()

Returns the string representation of this module.

Methods declared in class java.lang.Object

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

Methods declared in interface java.lang.reflect.AnnotatedElement

getAnnotationsByType, getDeclaredAnnotation, getDeclaredAnnotationsByType, isAnnotationPresent

Methods

isNamed

public boolean isNamed()

Returns true if this module is a named module.

Returns:
true if this is a named module
See Also:
ClassLoader.getUnnamedModule()

getName

public String getName()

Returns the module name or null if this module is an unnamed module.

Returns:
The module name

getClassLoader

public ClassLoader getClassLoader()

Returns the ClassLoader for this module.

If there is a security manager then its checkPermission method if first called with a RuntimePermission("getClassLoader") permission to check that the caller is allowed to get access to the class loader.

Returns:
The class loader for this module
Throws:
SecurityException - If denied by the security manager

getDescriptor

public ModuleDescriptor getDescriptor()

Returns the module descriptor for this module or null if this module is an unnamed module.

Returns:
The module descriptor for this module

getLayer

public ModuleLayer getLayer()

Returns the module layer that contains this module or null if this module is not in a module layer. A module layer contains named modules and therefore this method always returns null when invoked on an unnamed module.

Dynamic modules are named modules that are generated at runtime. A dynamic module may or may not be in a module layer.

Returns:
The module layer that contains this module
See Also:
Proxy

canRead

public boolean canRead(Module other)

Indicates if this module reads the given module. This method returns true if invoked to test if this module reads itself. It also returns true if invoked on an unnamed module (as unnamed modules read all modules).

Parameters:
other - The other module
Returns:
true if this module reads other
See Also:
addReads(Module)

addReads

public Module addReads(Module other)

If the caller's module is this module then update this module to read the given module. This method is a no-op if other is this module (all modules read themselves), this module is an unnamed module (as unnamed modules read all modules), or this module already reads other.

Implementation Note:
Read edges added by this method are weak and do not prevent other from being GC'ed when this module is strongly reachable.
Parameters:
other - The other module
Returns:
this module
Throws:
IllegalCallerException - If this is a named module and the caller's module is not this module
See Also:
canRead(java.lang.Module)

isExported

public boolean isExported(String pn,
                          Module other)

Returns true if this module exports the given package to at least the given module.

This method returns true if invoked to test if a package in this module is exported to itself. It always returns true when invoked on an unnamed module. A package that is open to the given module is considered exported to that module at run-time and so this method returns true if the package is open to the given module.

This method does not check if the given module reads this module.

Parameters:
pn - The package name
other - The other module
Returns:
true if this module exports the package to at least the given module
See Also:
ModuleDescriptor.exports(), addExports(String,Module)

isOpen

public boolean isOpen(String pn,
                      Module other)

Returns true if this module has opened a package to at least the given module.

This method returns true if invoked to test if a package in this module is open to itself. It returns true when invoked on an open module with a package in the module. It always returns true when invoked on an unnamed module.

This method does not check if the given module reads this module.

Parameters:
pn - The package name
other - The other module
Returns:
true if this module has opened the package to at least the given module
See Also:
ModuleDescriptor.opens(), addOpens(String,Module), AccessibleObject.setAccessible(boolean), MethodHandles.privateLookupIn(java.lang.Class<?>, java.lang.invoke.MethodHandles.Lookup)

isExported

public boolean isExported(String pn)

Returns true if this module exports the given package unconditionally.

This method always returns true when invoked on an unnamed module. A package that is opened unconditionally is considered exported unconditionally at run-time and so this method returns true if the package is opened unconditionally.

This method does not check if the given module reads this module.

Parameters:
pn - The package name
Returns:
true if this module exports the package unconditionally
See Also:
ModuleDescriptor.exports()

isOpen

public boolean isOpen(String pn)

Returns true if this module has opened a package unconditionally.

This method always returns true when invoked on an unnamed module. Additionally, it always returns true when invoked on an open module with a package in the module.

This method does not check if the given module reads this module.

Parameters:
pn - The package name
Returns:
true if this module has opened the package unconditionally
See Also:
ModuleDescriptor.opens()

addExports

public Module addExports(String pn,
                         Module other)

If the caller's module is this module then update this module to export the given package to the given module.

This method has no effect if the package is already exported (or open) to the given module.

API Note:
As specified in section 5.4.3 of the The Java™ Virtual Machine Specification , if an attempt to resolve a symbolic reference fails because of a linkage error, then subsequent attempts to resolve the reference always fail with the same error that was thrown as a result of the initial resolution attempt.
Parameters:
pn - The package name
other - The module
Returns:
this module
Throws:
IllegalArgumentException - If pn is null, or this is a named module and the package pn is not a package in this module
IllegalCallerException - If this is a named module and the caller's module is not this module
See Also:
isExported(String,Module)

addOpens

public Module addOpens(String pn,
                       Module other)

If this module has opened a package to at least the caller module then update this module to open the package to the given module. Opening a package with this method allows all types in the package, and all their members, not just public types and their public members, to be reflected on by the given module when using APIs that support private access or a way to bypass or suppress default Java language access control checks.

This method has no effect if the package is already open to the given module.

API Note:
This method can be used for cases where a consumer module uses a qualified opens to open a package to an API module but where the reflective access to the members of classes in the consumer module is delegated to code in another module. Code in the API module can use this method to open the package in the consumer module to the other module.
Parameters:
pn - The package name
other - The module
Returns:
this module
Throws:
IllegalArgumentException - If pn is null, or this is a named module and the package pn is not a package in this module
IllegalCallerException - If this is a named module and this module has not opened the package to at least the caller's module
See Also:
isOpen(String,Module), AccessibleObject.setAccessible(boolean), MethodHandles.privateLookupIn(java.lang.Class<?>, java.lang.invoke.MethodHandles.Lookup)

addUses

public Module addUses(Class<?> service)

If the caller's module is this module then update this module to add a service dependence on the given service type. This method is intended for use by frameworks that invoke ServiceLoader on behalf of other modules or where the framework is passed a reference to the service type by other code. This method is a no-op when invoked on an unnamed module or an automatic module.

This method does not cause resolveAndBind to be re-run.

Parameters:
service - The service type
Returns:
this module
Throws:
IllegalCallerException - If this is a named module and the caller's module is not this module
See Also:
canUse(Class), ModuleDescriptor.uses()

canUse

public boolean canUse(Class<?> service)

Indicates if this module has a service dependence on the given service type. This method always returns true when invoked on an unnamed module or an automatic module.

Parameters:
service - The service type
Returns:
true if this module uses service type st
See Also:
addUses(Class)

getPackages

public Set<String> getPackages()

Returns the set of package names for the packages in this module.

For named modules, the returned set contains an element for each package in the module.

For unnamed modules, this method is the equivalent to invoking the getDefinedPackages method of this module's class loader and returning the set of package names.

Returns:
the set of the package names of the packages in this module

getAnnotation

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

Returns this element's annotation for the specified type if such an annotation is present, else null. This method returns null when invoked on an unnamed module.

Specified by:
getAnnotation in interface AnnotatedElement
Type Parameters:
T - 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

getAnnotations

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. This method returns an empty array when invoked on an unnamed module.

Specified by:
getAnnotations in interface AnnotatedElement
Returns:
annotations present on this element

getDeclaredAnnotations

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. This method returns an empty array when invoked on an unnamed module.

Specified by:
getDeclaredAnnotations in interface AnnotatedElement
Returns:
annotations directly present on this element

getResourceAsStream

public InputStream getResourceAsStream(String name)
                                throws IOException

Returns an input stream for reading a resource in this module. The name parameter is a '/'-separated path name that identifies the resource. As with Class.getResourceAsStream, this method delegates to the module's class loader findResource(String,String) method, invoking it with the module name (or null when the module is unnamed) and the name of the resource. If the resource name has a leading slash then it is dropped before delegation.

A resource in a named module may be encapsulated so that it cannot be located by code in other modules. Whether a resource can be located or not is determined as follows:

  • If the resource name ends with ".class" then it is not encapsulated.
  • A package name is derived from the resource name. If the package name is a package in the module then the resource can only be located by the caller of this method when the package is open to at least the caller's module. If the resource is not in a package in the module then the resource is not encapsulated.

In the above, the package name for a resource is derived from the subsequence of characters that precedes the last '/' in the name and then replacing each '/' character in the subsequence with '.'. A leading slash is ignored when deriving the package name. As an example, the package name derived for a resource named "a/b/c/foo.properties" is "a.b.c". A resource name with the name "META-INF/MANIFEST.MF" is never encapsulated because "META-INF" is not a legal package name.

This method returns null if the resource is not in this module, the resource is encapsulated and cannot be located by the caller, or access to the resource is denied by the security manager.

Parameters:
name - The resource name
Returns:
An input stream for reading the resource or null
Throws:
IOException - If an I/O error occurs
See Also:
Class.getResourceAsStream(String)

toString

public String toString()

Returns the string representation of this module. For a named module, the representation is the string "module", followed by a space, and then the module name. For an unnamed module, the representation is the string "unnamed module", followed by a space, and then an implementation specific string that identifies the unnamed module.

Overrides:
toString in class Object
Returns:
The string representation of this module

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Documentation extracted from Debian's OpenJDK Development Kit package.
Licensed under the GNU General Public License, version 2, with the Classpath Exception.
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https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/lang/Module.html