Module java.base

Package java.lang.reflect

Class AccessibleObject

java.lang.Object

java.lang.reflect.AccessibleObject

All Implemented Interfaces:

AnnotatedElement

Direct Known Subclasses:

Executable, Field

public class AccessibleObject
extends Object
implements AnnotatedElement

The AccessibleObject class is the base class for Field, Method, and Constructor objects (known as reflected objects). It provides the ability to flag a reflected object as suppressing checks for Java language access control when it is used. This permits sophisticated applications with sufficient privilege, such as Java Object Serialization or other persistence mechanisms, to manipulate objects in a manner that would normally be prohibited.

Java language access control prevents use of private members outside their top-level class; package access members outside their package; protected members outside their package or subclasses; and public members outside their module unless they are declared in an exported package and the user reads their module. By default, Java language access control is enforced (with one variation) when Fields, Methods, or Constructors are used to get or set fields, to invoke methods, or to create and initialize new instances of classes, respectively. Every reflected object checks that the code using it is in an appropriate class, package, or module. The check when invoked by JNI code with no Java class on the stack only succeeds if the member and the declaring class are public, and the class is in a package that is exported to all modules.

The one variation from Java language access control is that the checks by reflected objects assume readability. That is, the module containing the use of a reflected object is assumed to read the module in which the underlying field, method, or constructor is declared.

Whether the checks for Java language access control can be suppressed (and thus, whether access can be enabled) depends on whether the reflected object corresponds to a member in an exported or open package (see setAccessible(boolean)).

See Java Language Specification:

6.6 Access Control

Since:

1.2

Constructor Summary

Constructors

Modifier	Constructor	Description
protected	AccessibleObject()	Constructor: only used by the Java Virtual Machine.

Method Summary

Modifier and Type	Method	Description
boolean	canAccess(Object obj)	Test if the caller can access this reflected object.
<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.
<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.
boolean	isAccessible()	Deprecated. This method is deprecated because its name hints that it checks if the reflected object is accessible when it actually indicates if the checks for Java language access control are suppressed.
boolean	isAnnotationPresent(Class<? extends Annotation> annotationClass)	Returns true if an annotation for the specified type is present on this element, else false.
void	setAccessible(boolean flag)	Set the accessible flag for this reflected object to the indicated boolean value.
static void	setAccessible(AccessibleObject[] array, boolean flag)	Convenience method to set the accessible flag for an array of reflected objects with a single security check (for efficiency).
boolean	trySetAccessible()	Set the accessible flag for this reflected object to true if possible.

Methods declared in class java.lang.Object

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

Constructor Details

AccessibleObject

protected AccessibleObject()

Constructor: only used by the Java Virtual Machine.

Method Details

setAccessible

public static void setAccessible(AccessibleObject[] array,
 boolean flag)

Convenience method to set the accessible flag for an array of reflected objects with a single security check (for efficiency).

This method may be used to enable access to all reflected objects in the array when access to each reflected object can be enabled as specified by setAccessible(boolean).

If there is a security manager, its checkPermission method is first called with a ReflectPermission("suppressAccessChecks") permission.

A SecurityException is also thrown if any of the elements of the input array is a Constructor object for the class java.lang.Class and flag is true.

Parameters:

array - the array of AccessibleObjects

flag - the new value for the accessible flag in each object

Throws:

InaccessibleObjectException - if access cannot be enabled for all objects in the array

SecurityException - if the request is denied by the security manager or an element in the array is a constructor for java.lang.Class

See Also:

SecurityManager.checkPermission(java.security.Permission), ReflectPermission

setAccessible

public void setAccessible(boolean flag)

Set the accessible flag for this reflected object to the indicated boolean value. A value of true indicates that the reflected object should suppress checks for Java language access control when it is used. A value of false indicates that the reflected object should enforce checks for Java language access control when it is used, with the variation noted in the class description.

This method may be used by a caller in class C to enable access to a member of declaring class D if any of the following hold:

• C and D are in the same module.
• The member is public and D is public in a package that the module containing D exports to at least the module containing C.
• The member is protected static, D is public in a package that the module containing D exports to at least the module containing C, and C is a subclass of D.
• D is in a package that the module containing D opens to at least the module containing C. All packages in unnamed and open modules are open to all modules and so this method always succeeds when D is in an unnamed or open module.

This method cannot be used to enable access to private members, members with default (package) access, protected instance members, or protected constructors when the declaring class is in a different module to the caller and the package containing the declaring class is not open to the caller's module.

This method cannot be used to enable write access to a non-modifiable final field. The following fields are non-modifiable:

• static final fields declared in any class or interface
• final fields declared in a hidden class
• final fields declared in a record

The accessible flag when true suppresses Java language access control checks to only enable read access to these non-modifiable final fields.

If there is a security manager, its checkPermission method is first called with a ReflectPermission("suppressAccessChecks") permission.

Parameters:

flag - the new value for the accessible flag

Throws:

InaccessibleObjectException - if access cannot be enabled

SecurityException - if the request is denied by the security manager

See Also:

trySetAccessible(), MethodHandles.privateLookupIn(java.lang.Class<?>, java.lang.invoke.MethodHandles.Lookup)

trySetAccessible

public final boolean trySetAccessible()

Set the accessible flag for this reflected object to true if possible. This method sets the accessible flag, as if by invoking setAccessible(true), and returns the possibly-updated value for the accessible flag. If access cannot be enabled, i.e. the checks or Java language access control cannot be suppressed, this method returns false (as opposed to setAccessible(true) throwing InaccessibleObjectException when it fails).

This method is a no-op if the accessible flag for this reflected object is true.

For example, a caller can invoke trySetAccessible on a Method object for a private instance method p.T::privateMethod to suppress the checks for Java language access control when the Method is invoked. If p.T class is in a different module to the caller and package p is open to at least the caller's module, the code below successfully sets the accessible flag to true.

 
     p.T obj = ....;  // instance of p.T
     :
     Method m = p.T.class.getDeclaredMethod("privateMethod");
     if (m.trySetAccessible()) {
         m.invoke(obj);
     } else {
         // package p is not opened to the caller to access private member of T
         ...
     }
 

If there is a security manager, its checkPermission method is first called with a ReflectPermission("suppressAccessChecks") permission.

Returns:

true if the accessible flag is set to true; false if access cannot be enabled.

Throws:

SecurityException - if the request is denied by the security manager

Since:

9

See Also:

MethodHandles.privateLookupIn(java.lang.Class<?>, java.lang.invoke.MethodHandles.Lookup)

isAccessible

@Deprecated(since="9")
public boolean isAccessible()

Deprecated.

This method is deprecated because its name hints that it checks if the reflected object is accessible when it actually indicates if the checks for Java language access control are suppressed. This method may return false on a reflected object that is accessible to the caller. To test if this reflected object is accessible, it should use canAccess(Object).

Get the value of the accessible flag for this reflected object.

Returns:

the value of the object's accessible flag

canAccess

public final boolean canAccess(Object obj)

Test if the caller can access this reflected object. If this reflected object corresponds to an instance method or field then this method tests if the caller can access the given obj with the reflected object. For instance methods or fields then the obj argument must be an instance of the declaring class. For static members and constructors then obj must be null.

This method returns true if the accessible flag is set to true, i.e. the checks for Java language access control are suppressed, or if the caller can access the member as specified in The Java Language Specification, with the variation noted in the class description.

Parameters:

obj - an instance object of the declaring class of this reflected object if it is an instance method or field

Returns:

true if the caller can access this reflected object.

Throws:

IllegalArgumentException -

• if this reflected object is a static member or constructor and the given obj is non-null, or
• if this reflected object is an instance method or field and the given obj is null or of type that is not a subclass of the declaring class of the member.

See Java Language Specification:

6.6 Access Control

Since:

9

See Also:

trySetAccessible(), setAccessible(boolean)

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.

Note that any annotation returned by this method is a declaration annotation.

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

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

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 <T extends Annotation> 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 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.

Note that any annotations returned by this method are declaration annotations.

Specified by:

getAnnotationsByType 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:

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()

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.

Note that any annotations returned by this method are declaration annotations.

Specified by:

getAnnotations in interface AnnotatedElement

Returns:

annotations present on this element

Since:

1.5

getDeclaredAnnotation

public <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. This method ignores inherited annotations. (Returns null if no annotations are directly present on this element.)

Note that any annotation returned by this method is a declaration annotation.

Specified by:

getDeclaredAnnotation in interface AnnotatedElement

Type Parameters:

T - 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 <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. 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.

Note that any annotations returned by this method are declaration annotations.

Specified by:

getDeclaredAnnotationsByType in interface AnnotatedElement

Type Parameters:

T - 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()

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.

Note that any annotations returned by this method are declaration annotations.

Specified by:

getDeclaredAnnotations in interface AnnotatedElement

Returns:

annotations directly present on this element

Since:

1.5