Module java.base
Package java.lang.reflect

Class 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 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)).

    Since:
    1.2
    See The Java™ Language Specification:
    6.6 Access Control

    • Constructor Detail

      • AccessibleObject

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

    • Method Detail

      • 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.

        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.
        Since:
        9
        See Also:
        trySetAccessible(), setAccessible(boolean)
        See The Java™ Language Specification:
        6.6 Access Control

      • getAnnotation

        public <T extends Annotation> T getAnnotation​(Class<T> 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:
        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

        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 <T extends Annotation> T[] getAnnotationsByType​(Class<T> 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:
        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()
        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 <T extends Annotation> T getDeclaredAnnotation​(Class<T> 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:
        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)
        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:
        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()
        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