Class (Java SE 15 & JDK 15)
source link: https://docs.oracle.com/en/java/javase/15/docs/api/java.base/java/lang/Class.html
Go to the source link to view the article. You can view the picture content, updated content and better typesetting reading experience. If the link is broken, please click the button below to view the snapshot at that time.
T
- the type of the class modeled by this Class
object. For example, the type of String.class
is
Class<String>
. Use Class<?>
if the class being modeled is
unknown.
All Implemented Interfaces:
Serializable
, Constable
, TypeDescriptor
, TypeDescriptor.OfField<Class<?>>
, AnnotatedElement
, GenericDeclaration
, Type
public final class Class<T> extends Object implements Serializable, GenericDeclaration, Type, AnnotatedElement, TypeDescriptor.OfField<Class<?>>, Constable
Instances of the class Class
represent classes and
interfaces in a running Java application. An enum type and a record
type are kinds of class; an annotation type is a kind of
interface. Every array also belongs to a class that is reflected as
a Class
object that is shared by all arrays with the same
element type and number of dimensions. The primitive Java types
(boolean
, byte
, char
, short
,
int
, long
, float
, and double
), and the
keyword void
are also represented as Class
objects.
Class
has no public constructor. Instead a Class
object is constructed automatically by the Java Virtual Machine when
a class is derived from the bytes of a class
file through
the invocation of one of the following methods:
The methods of class Class
expose many characteristics of a
class or interface. Most characteristics are derived from the class
file that the class loader passed to the Java Virtual Machine or
from the class
file passed to Lookup::defineClass
or Lookup::defineHiddenClass
.
A few characteristics are determined by the class loading environment
at run time, such as the module returned by getModule()
.
The following example uses a Class
object to print the
class name of an object:
void printClassName(Object obj) { System.out.println("The class of " + obj + " is " + obj.getClass().getName()); }
It is also possible to get the Class
object for a named
type (or for void
) using a class literal.
For example:
System.out.println("The name of class Foo is: "+Foo.class.getName());
Some methods of class Class
expose whether the declaration of
a class or interface in Java source code was enclosed within
another declaration. Other methods describe how a class or interface
is situated in a nest. A nest is a set of
classes and interfaces, in the same run-time package, that
allow mutual access to their private
members.
The classes and interfaces are known as nestmates.
One nestmate acts as the
nest host, and enumerates the other nestmates which
belong to the nest; each of them in turn records it as the nest host.
The classes and interfaces which belong to a nest, including its host, are
determined when
class
files are generated, for example, a Java compiler
will typically record a top-level class as the host of a nest where the
other members are the classes and interfaces whose declarations are
enclosed within the top-level class declaration.
A class or interface created by the invocation of
Lookup::defineHiddenClass
is a hidden
class or interface.
All kinds of class, including enum types and record types, may be
hidden classes; all kinds of interface, including annotation types,
may be hidden interfaces.
The name of a hidden class or interface is not a binary name, which means the following:
- A hidden class or interface cannot be referenced by the constant pools of other classes and interfaces.
- A hidden class or interface cannot be described in
nominal form by
Class::describeConstable
,ClassDesc::of
, orClassDesc::ofDescriptor
. - A hidden class or interface cannot be discovered by
Class::forName
orClassLoader::loadClass
.
A hidden class or interface is never an array class, but may be
the element type of an array. In all other respects, the fact that
a class or interface is hidden has no bearing on the characteristics
exposed by the methods of class Class
.
See Java Language Specification:
15.8.2 Class Literals
Since:
See Also:
ClassLoader.defineClass(byte[], int, int)
,
Serialized Form
-
Method Summary
Modifier and Type Method Description
Class<?>
arrayType()
Returns aClass
for an array type whose component type is described by this Class.<U> Class<? extends U>
asSubclass(Class<U> clazz)
Casts thisClass
object to represent a subclass of the class represented by the specified class object.Casts an object to the class or interface represented by thisClass
object.Class<?>
componentType()
Returns the component type of thisClass
, if it describes an array type, ornull
otherwise.Optional<ClassDesc>
describeConstable()
Returns a nominal descriptor for this instance, if one can be constructed, or an emptyOptional
if one cannot be.Returns the descriptor string of the entity (class, interface, array class, primitive type, orvoid
) represented by thisClass
object.boolean
desiredAssertionStatus()
Returns the assertion status that would be assigned to this class if it were to be initialized at the time this method is invoked.static Class<?>
forName(Module module, String name)
Returns theClass
with the given binary name in the given module.static Class<?>
forName(String className)
Returns theClass
object associated with the class or interface with the given string name.static Class<?>
forName(String name, boolean initialize, ClassLoader loader)
Returns theClass
object associated with the class or interface with the given string name, using the given class loader.AnnotatedType[]
getAnnotatedInterfaces()
Returns an array ofAnnotatedType
objects that represent the use of types to specify superinterfaces of the entity represented by thisClass
object.AnnotatedType
getAnnotatedSuperclass()
Returns anAnnotatedType
object that represents the use of a type to specify the superclass of the entity represented by thisClass
object.<A extends Annotation>
AgetAnnotation(Class<A> annotationClass)
Returns this element's annotation for the specified type if such an annotation is present, else null.Returns annotations that are present on this element.<A extends Annotation>
A[]getAnnotationsByType(Class<A> annotationClass)
Returns annotations that are associated with this element.Returns the canonical name of the underlying class as defined by The Java Language Specification.Class<?>[]
getClasses()
Returns an array containingClass
objects representing all the public classes and interfaces that are members of the class represented by thisClass
object.Returns the class loader for the class.Class<?>
getComponentType()
Returns theClass
representing the component type of an array.Constructor<T>
getConstructor(Class<?>... parameterTypes)
Returns aConstructor
object that reflects the specified public constructor of the class represented by thisClass
object.Constructor<?>[]
getConstructors()
Returns an array containingConstructor
objects reflecting all the public constructors of the class represented by thisClass
object.<A extends Annotation>
AgetDeclaredAnnotation(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.Class<?>[]
getDeclaredClasses()
Returns an array ofClass
objects reflecting all the classes and interfaces declared as members of the class represented by thisClass
object.Constructor<T>
getDeclaredConstructor(Class<?>... parameterTypes)
Returns aConstructor
object that reflects the specified constructor of the class or interface represented by thisClass
object.Constructor<?>[]
getDeclaredConstructors()
Returns an array ofConstructor
objects reflecting all the constructors declared by the class represented by thisClass
object.Field
getDeclaredField(String name)
Returns aField
object that reflects the specified declared field of the class or interface represented by thisClass
object.Returns an array ofField
objects reflecting all the fields declared by the class or interface represented by thisClass
object.Method
getDeclaredMethod(String name, Class<?>... parameterTypes)
Returns aMethod
object that reflects the specified declared method of the class or interface represented by thisClass
object.Returns an array containingMethod
objects reflecting all the declared methods of the class or interface represented by thisClass
object, including public, protected, default (package) access, and private methods, but excluding inherited methods.Class<?>
getDeclaringClass()
If the class or interface represented by thisClass
object is a member of another class, returns theClass
object representing the class in which it was declared.Class<?>
getEnclosingClass()
Returns the immediately enclosing class of the underlying class.Constructor<?>
getEnclosingConstructor()
If thisClass
object represents a local or anonymous class within a constructor, returns aConstructor
object representing the immediately enclosing constructor of the underlying class.If thisClass
object represents a local or anonymous class within a method, returns aMethod
object representing the immediately enclosing method of the underlying class.T[]
getEnumConstants()
Returns the elements of this enum class or null if this Class object does not represent an enum type.Returns aField
object that reflects the specified public member field of the class or interface represented by thisClass
object.Returns an array containingField
objects reflecting all the accessible public fields of the class or interface represented by thisClass
object.Returns theType
s representing the interfaces directly implemented by the class or interface represented by thisClass
object.Returns theType
representing the direct superclass of the entity (class, interface, primitive type or void) represented by thisClass
object.Class<?>[]
getInterfaces()
Returns the interfaces directly implemented by the class or interface represented by thisClass
object.Method
getMethod(String name, Class<?>... parameterTypes)
Returns aMethod
object that reflects the specified public member method of the class or interface represented by thisClass
object.Method[]
getMethods()
Returns an array containingMethod
objects reflecting all the public methods of the class or interface represented by thisClass
object, including those declared by the class or interface and those inherited from superclasses and superinterfaces.int
getModifiers()
Returns the Java language modifiers for this class or interface, encoded in an integer.Returns the module that this class or interface is a member of.Returns the name of the entity (class, interface, array class, primitive type, or void) represented by thisClass
object.Class<?>
getNestHost()
Returns the nest host of the nest to which the class or interface represented by thisClass
object belongs.Class<?>[]
getNestMembers()
Returns an array containingClass
objects representing all the classes and interfaces that are members of the nest to which the class or interface represented by thisClass
object belongs.Gets the package of this class.Returns the fully qualified package name.ProtectionDomain
getProtectionDomain()
Returns theProtectionDomain
of this class.RecordComponent[]
getRecordComponents()
Associated with records, a preview feature of the Java language.Returns an array of
RecordComponent
objects representing all the record components of this record class, ornull
if this class is not a record class.URL
getResource(String name)
Finds a resource with a given name.InputStream
getResourceAsStream(String name)
Finds a resource with a given name.Object[]
getSigners()
Gets the signers of this class.Returns the simple name of the underlying class as given in the source code.Class<? super T>
getSuperclass()
Returns theClass
representing the direct superclass of the entity (class, interface, primitive type or void) represented by thisClass
.Return an informative string for the name of this type.TypeVariable<Class<T>>[]
getTypeParameters()
Returns an array ofTypeVariable
objects that represent the type variables declared by the generic declaration represented by thisGenericDeclaration
object, in declaration order.boolean
isAnnotation()
Returns true if thisClass
object represents an annotation type.boolean
isAnnotationPresent(Class<? extends Annotation> annotationClass)
Returns true if an annotation for the specified type is present on this element, else false.boolean
isAnonymousClass()
Returnstrue
if and only if the underlying class is an anonymous class.boolean
isArray()
Determines if thisClass
object represents an array class.boolean
isAssignableFrom(Class<?> cls)
Determines if the class or interface represented by thisClass
object is either the same as, or is a superclass or superinterface of, the class or interface represented by the specifiedClass
parameter.boolean
isEnum()
Returns true if and only if this class was declared as an enum in the source code.boolean
isHidden()
Returnstrue
if and only if the underlying class is a hidden class.boolean
isInstance(Object obj)
Determines if the specifiedObject
is assignment-compatible with the object represented by thisClass
.boolean
isInterface()
Determines if thisClass
object represents an interface type.boolean
isLocalClass()
Returnstrue
if and only if the underlying class is a local class.boolean
isMemberClass()
Returnstrue
if and only if the underlying class is a member class.boolean
isNestmateOf(Class<?> c)
Determines if the givenClass
is a nestmate of the class or interface represented by thisClass
object.boolean
isPrimitive()
Determines if the specifiedClass
object represents a primitive type.boolean
isRecord()
Associated with records, a preview feature of the Java language.Returns
true
if and only if this class is a record class.boolean
isSealed()
*Associated with sealed classes, a preview feature of the Java language.Returns
true
if and only if thisClass
object represents a sealed class or interface.boolean
isSynthetic()
Returnstrue
if and only if this class has the synthetic modifier bit set.T
newInstance()
Deprecated.This method propagates any exception thrown by the nullary constructor, including a checked exception.ClassDesc[]
permittedSubclasses()
Associated with sealed classes, a preview feature of the Java language.Returns an array containing
ClassDesc
objects representing all the direct subclasses or direct implementation classes permitted to extend or implement this class or interface if it is sealed.Returns a string describing thisClass
, including information about modifiers and type parameters.Converts the object to a string.
-
Method Details
-
toString
public String toString()Converts the object to a string. The string representation is the string "class" or "interface", followed by a space, and then by the name of the class in the format returned byOverrides:getName
. If thisClass
object represents a primitive type, this method returns the name of the primitive type. If thisClass
object represents void this method returns "void". If thisClass
object represents an array type, this method returns "class " followed bygetName
.toString
in classObject
Returns: a string representation of thisClass
object. -
toGenericString
public String toGenericString()Returns a string describing this
Class
, including information about modifiers and type parameters.The string is formatted as a list of type modifiers, if any, followed by the kind of type (empty string for primitive types and
class
,enum
,interface
,@interface
, orrecord
as appropriate), followed by the type's name, followed by an angle-bracketed comma-separated list of the type's type parameters, if any, including informative bounds on the type parameters, if any.A space is used to separate modifiers from one another and to separate any modifiers from the kind of type. The modifiers occur in canonical order. If there are no type parameters, the type parameter list is elided.
For an array type, the string starts with the type name, followed by an angle-bracketed comma-separated list of the type's type parameters, if any, followed by a sequence of
[]
characters, one set of brackets per dimension of the array.Note that since information about the runtime representation of a type is being generated, modifiers not present on the originating source code or illegal on the originating source code may be present.
Returns: a string describing this
Class
, including information about modifiers and type parameters Since: -
forName
Returns the
Class
object associated with the class or interface with the given string name. Invoking this method is equivalent to:Class.forName(className, true, currentLoader)
where
currentLoader
denotes the defining class loader of the current class.For example, the following code fragment returns the runtime
Class
descriptor for the class namedjava.lang.Thread
:Class t = Class.forName("java.lang.Thread")
A call to
forName("X")
causes the class namedX
to be initialized.Parameters:
className
- the fully qualified name of the desired class. Returns: theClass
object for the class with the specified name. Throws:LinkageError
- if the linkage failsExceptionInInitializerError
- if the initialization provoked by this method failsClassNotFoundException
- if the class cannot be located See Java Language Specification:12.2 Loading of Classes and Interfaces
12.3 Linking of Classes and Interfaces
12.4 Initialization of Classes and Interfaces -
forName
public static Class<?> forName(String name, boolean initialize, ClassLoader loader) throws ClassNotFoundExceptionReturns the
Class
object associated with the class or interface with the given string name, using the given class loader. Given the fully qualified name for a class or interface (in the same format returned bygetName
) this method attempts to locate and load the class or interface. The specified class loader is used to load the class or interface. If the parameterloader
is null, the class is loaded through the bootstrap class loader. The class is initialized only if theinitialize
parameter istrue
and if it has not been initialized earlier.If
name
denotes a primitive type or void, an attempt will be made to locate a user-defined class in the unnamed package whose name isname
. Therefore, this method cannot be used to obtain any of theClass
objects representing primitive types or void.If
name
denotes an array class, the component type of the array class is loaded but not initialized.For example, in an instance method the expression:
Class.forName("Foo")
is equivalent to:
Class.forName("Foo", true, this.getClass().getClassLoader())
Note that this method throws errors related to loading, linking or initializing as specified in Sections 12.2, 12.3, and 12.4 of The Java Language Specification. Note that this method does not check whether the requested class is accessible to its caller.
Parameters:
name
- fully qualified name of the desired classinitialize
- iftrue
the class will be initialized (which implies linking). See Section 12.4 of The Java Language Specification.loader
- class loader from which the class must be loaded Returns: class object representing the desired class Throws:LinkageError
- if the linkage failsExceptionInInitializerError
- if the initialization provoked by this method failsClassNotFoundException
- if the class cannot be located by the specified class loaderSecurityException
- if a security manager is present, and theloader
isnull
, and the caller's class loader is notnull
, and the caller does not have theRuntimePermission
("getClassLoader")
See Java Language Specification:12.2 Loading of Classes and Interfaces
12.3 Linking of Classes and Interfaces
12.4 Initialization of Classes and Interfaces
Since:See Also:
forName(String)
,ClassLoader
-
forName
API Note: This method returnsReturns the
Class
with the given binary name in the given module.This method attempts to locate and load the class or interface. It does not link the class, and does not run the class initializer. If the class is not found, this method returns
null
.If the class loader of the given module defines other modules and the given name is a class defined in a different module, this method returns
null
after the class is loaded.This method does not check whether the requested class is accessible to its caller.
null
on failure rather than throwing aClassNotFoundException
, as is done by theforName(String, boolean, ClassLoader)
method. The security check is a stack-based permission check if the caller loads a class in another module. Parameters:module
- A modulename
- The binary name of the class Returns:Class
object of the given name defined in the given module;null
if not found. Throws:NullPointerException
- if the given module or name isnull
LinkageError
- if the linkage failsSecurityException
-- if the caller is not the specified module and
RuntimePermission("getClassLoader")
permission is denied; or - access to the module content is denied. For example,
permission check will be performed when a class loader calls
ModuleReader.open(String)
to read the bytes of a class file in a module.
See Java Language Specification:
12.2 Loading of Classes and Interfaces
12.3 Linking of Classes and Interfaces
Since: - if the caller is not the specified module and
-
newInstance
Deprecated.This method propagates any exception thrown by the nullary constructor, including a checked exception. Use of this method effectively bypasses the compile-time exception checking that would otherwise be performed by the compiler. The
Constructor.newInstance
method avoids this problem by wrapping any exception thrown by the constructor in a (checked)InvocationTargetException
.The call
clazz.newInstance()
can be replaced by
clazz.getDeclaredConstructor().newInstance()
The latter sequence of calls is inferred to be able to throw the additional exception types
InvocationTargetException
andNoSuchMethodException
. Both of these exception types are subclasses ofReflectiveOperationException
.Creates a new instance of the class represented by thisReturns: a newly allocated instance of the class represented by this object. Throws:Class
object. The class is instantiated as if by anew
expression with an empty argument list. The class is initialized if it has not already been initialized.IllegalAccessException
- if the class or its nullary constructor is not accessible.InstantiationException
- if thisClass
represents an abstract class, an interface, an array class, a primitive type, or void; or if the class has no nullary constructor; or if the instantiation fails for some other reason.ExceptionInInitializerError
- if the initialization provoked by this method fails.SecurityException
- If a security manager, s, is present and the caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation ofs.checkPackageAccess()
denies access to the package of this class. -
isInstance
public boolean isInstance(Object obj)Determines if the specified
Object
is assignment-compatible with the object represented by thisClass
. This method is the dynamic equivalent of the Java languageinstanceof
operator. The method returnstrue
if the specifiedObject
argument is non-null and can be cast to the reference type represented by thisClass
object without raising aClassCastException.
It returnsfalse
otherwise.Specifically, if this
Class
object represents a declared class, this method returnstrue
if the specifiedObject
argument is an instance of the represented class (or of any of its subclasses); it returnsfalse
otherwise. If thisClass
object represents an array class, this method returnstrue
if the specifiedObject
argument can be converted to an object of the array class by an identity conversion or by a widening reference conversion; it returnsfalse
otherwise. If thisClass
object represents an interface, this method returnstrue
if the class or any superclass of the specifiedObject
argument implements this interface; it returnsfalse
otherwise. If thisClass
object represents a primitive type, this method returnsfalse
.Parameters:
obj
- the object to check Returns: true ifobj
is an instance of this class Since: -
isAssignableFrom
public boolean isAssignableFrom(Class<?> cls)Determines if the class or interface represented by this
Class
object is either the same as, or is a superclass or superinterface of, the class or interface represented by the specifiedClass
parameter. It returnstrue
if so; otherwise it returnsfalse
. If thisClass
object represents a primitive type, this method returnstrue
if the specifiedClass
parameter is exactly thisClass
object; otherwise it returnsfalse
.Specifically, this method tests whether the type represented by the specified
Class
parameter can be converted to the type represented by thisClass
object via an identity conversion or via a widening reference conversion. See The Java Language Specification, sections 5.1.1 and 5.1.4, for details.Parameters:
cls
- theClass
object to be checked Returns: theboolean
value indicating whether objects of the typecls
can be assigned to objects of this class Throws:NullPointerException
- if the specified Class parameter is null. Since: -
isInterface
public boolean isInterface()Determines if thisReturns:Class
object represents an interface type.true
if thisClass
object represents an interface;false
otherwise. -
isArray
public boolean isArray()Determines if thisClass
object represents an array class.Specified by:
isArray
in interfaceTypeDescriptor.OfField<T>
Returns:true
if thisClass
object represents an array class;false
otherwise. Since: -
isPrimitive
public boolean isPrimitive()Determines if the specified
Class
object represents a primitive type.There are nine predefined
Class
objects to represent the eight primitive types and void. These are created by the Java Virtual Machine, and have the same names as the primitive types that they represent, namelyboolean
,byte
,char
,short
,int
,long
,float
, anddouble
.These objects may only be accessed via the following public static final variables, and are the only
Class
objects for which this method returnstrue
.Specified by:
isPrimitive
in interfaceTypeDescriptor.OfField<T>
Returns: true if and only if this class represents a primitive type Since:See Also:
Boolean.TYPE
,Character.TYPE
,Byte.TYPE
,Short.TYPE
,Integer.TYPE
,Long.TYPE
,Float.TYPE
,Double.TYPE
,Void.TYPE
-
isAnnotation
public boolean isAnnotation()Returns true if thisClass
object represents an annotation type. Note that if this method returns true,isInterface()
would also return true, as all annotation types are also interfaces.Returns:
true
if thisClass
object represents an annotation type;false
otherwise Since: -
isSynthetic
public boolean isSynthetic()Returnstrue
if and only if this class has the synthetic modifier bit set.Returns:
true
if and only if this class has the synthetic modifier bit set See Java Language Specification:13.1 The Form of a Binary
See Java Virtual Machine Specification:4.1 The
ClassFile
Structure
Since: -
getName
public String getName()Returns the name of the entity (class, interface, array class, primitive type, or void) represented by this
Class
object.If this
Class
object represents a class or interface, not an array class, then:- If the class or interface is not hidden, then the binary name of the class or interface is returned.
- If the class or interface is hidden, then the result is a string
of the form:
N + '/' + <suffix>
whereN
is the binary name indicated by theclass
file passed toLookup::defineHiddenClass
, and<suffix>
is an unqualified name.
If this
Class
object represents an array class, then the result is a string consisting of one or more '[
' characters representing the depth of the array nesting, followed by the element type as encoded using the following table:Element types and encodings Element Type Encoding
boolean
Z
byte
B
char
C
class or interface with binary name NL
N;
double
D
float
F
int
I
long
J
short
S
If this
Class
object represents a primitive type orvoid
, then the result is a string with the same spelling as the Java language keyword which corresponds to the primitive type orvoid
.Examples:
String.class.getName() returns "java.lang.String" byte.class.getName() returns "byte" (new Object[3]).getClass().getName() returns "[Ljava.lang.Object;" (new int[3][4][5][6][7][8][9]).getClass().getName() returns "[[[[[[[I"
Returns: the name of the class, interface, or other entity represented by this
Class
object. See Java Language Specification: -
getClassLoader
public ClassLoader getClassLoader()Returns: the class loader that loaded the class or interface represented by thisReturns the class loader for the class. Some implementations may use null to represent the bootstrap class loader. This method will return null in such implementations if this class was loaded by the bootstrap class loader.
If this
Class
object represents a primitive type or void, null is returned.Class
object. Throws:SecurityException
- if a security manager is present, and the caller's class loader is notnull
and is not the same as or an ancestor of the class loader for the class whose class loader is requested, and the caller does not have theRuntimePermission
("getClassLoader")
See Also:ClassLoader
,SecurityManager.checkPermission(java.security.Permission)
,RuntimePermission
-
getModule
public Module getModule()Returns the module that this class or interface is a member of.
If this class represents an array type then this method returns the
Module
for the element type. If this class represents a primitive type or void, then theModule
object for thejava.base
module is returned.If this class is in an unnamed module then the unnamed
Module
of the class loader for this class is returned.Returns: the module that this class or interface is a member of Since:
-
getTypeParameters
Returns an array ofTypeVariable
objects that represent the type variables declared by the generic declaration represented by thisGenericDeclaration
object, in declaration order. Returns an array of length 0 if the underlying generic declaration declares no type variables.Specified by:
getTypeParameters
in interfaceGenericDeclaration
Returns: an array ofTypeVariable
objects that represent the type variables declared by this generic declaration Throws:GenericSignatureFormatError
- if the generic signature of this generic declaration does not conform to the format specified in section 4.7.9 of The Java Virtual Machine Specification Since: -
getSuperclass
Returns theReturns: the direct superclass of the class represented by thisClass
representing the direct superclass of the entity (class, interface, primitive type or void) represented by thisClass
. If thisClass
represents either theObject
class, an interface, a primitive type, or void, then null is returned. If thisClass
object represents an array class then theClass
object representing theObject
class is returned.Class
object -
getGenericSuperclass
public Type getGenericSuperclass()Returns the
Type
representing the direct superclass of the entity (class, interface, primitive type or void) represented by thisClass
object.If the superclass is a parameterized type, the
Type
object returned must accurately reflect the actual type arguments used in the source code. The parameterized type representing the superclass is created if it had not been created before. See the declaration ofParameterizedType
for the semantics of the creation process for parameterized types. If thisClass
object represents either theObject
class, an interface, a primitive type, or void, then null is returned. If thisClass
object represents an array class then theClass
object representing theObject
class is returned.Returns: the direct superclass of the class represented by this
Class
object Throws:GenericSignatureFormatError
- if the generic class signature does not conform to the format specified in section 4.7.9 of The Java Virtual Machine SpecificationTypeNotPresentException
- if the generic superclass refers to a non-existent type declarationMalformedParameterizedTypeException
- if the generic superclass refers to a parameterized type that cannot be instantiated for any reason Since: -
getPackage
public Package getPackage()Returns: the package of this class.Gets the package of this class.
If this class represents an array type, a primitive type or void, this method returns
null
. -
getPackageName
public String getPackageName()Returns the fully qualified package name.
If this class is a top level class, then this method returns the fully qualified name of the package that the class is a member of, or the empty string if the class is in an unnamed package.
If this class is a member class, then this method is equivalent to invoking
getPackageName()
on the enclosing class.If this class is a local class or an anonymous class, then this method is equivalent to invoking
getPackageName()
on the declaring class of the enclosing method or enclosing constructor.If this class represents an array type then this method returns the package name of the element type. If this class represents a primitive type or void then the package name "
java.lang
" is returned.Returns: the fully qualified package name See Java Language Specification:
6.7 Fully Qualified Names
Since: -
getInterfaces
public Class<?>[] getInterfaces()Returns: an array of interfaces directly implemented by this classReturns the interfaces directly implemented by the class or interface represented by this
Class
object.If this
Class
object represents a class, the return value is an array containing objects representing all interfaces directly implemented by the class. The order of the interface objects in the array corresponds to the order of the interface names in theimplements
clause of the declaration of the class represented by thisClass
object. For example, given the declaration:class Shimmer implements FloorWax, DessertTopping { ... }
s
is an instance ofShimmer
; the value of the expression:s.getClass().getInterfaces()[0]
Class
object that represents interfaceFloorWax
; and the value of:s.getClass().getInterfaces()[1]
is the
Class
object that represents interfaceDessertTopping
.If this
Class
object represents an interface, the array contains objects representing all interfaces directly extended by the interface. The order of the interface objects in the array corresponds to the order of the interface names in theextends
clause of the declaration of the interface represented by thisClass
object.If this
Class
object represents a class or interface that implements no interfaces, the method returns an array of length 0.If this
Class
object represents a primitive type or void, the method returns an array of length 0.If this
Class
object represents an array type, the interfacesCloneable
andjava.io.Serializable
are returned in that order. -
getGenericInterfaces
public Type[] getGenericInterfaces()Returns the
Type
s representing the interfaces directly implemented by the class or interface represented by thisClass
object.If a superinterface is a parameterized type, the
Type
object returned for it must accurately reflect the actual type arguments used in the source code. The parameterized type representing each superinterface is created if it had not been created before. See the declaration ofParameterizedType
for the semantics of the creation process for parameterized types.If this
Class
object represents a class, the return value is an array containing objects representing all interfaces directly implemented by the class. The order of the interface objects in the array corresponds to the order of the interface names in theimplements
clause of the declaration of the class represented by thisClass
object.If this
Class
object represents an interface, the array contains objects representing all interfaces directly extended by the interface. The order of the interface objects in the array corresponds to the order of the interface names in theextends
clause of the declaration of the interface represented by thisClass
object.If this
Class
object represents a class or interface that implements no interfaces, the method returns an array of length 0.If this
Class
object represents a primitive type or void, the method returns an array of length 0.If this
Class
object represents an array type, the interfacesCloneable
andjava.io.Serializable
are returned in that order.Returns: an array of interfaces directly implemented by this class Throws:
GenericSignatureFormatError
- if the generic class signature does not conform to the format specified in section 4.7.9 of The Java Virtual Machine SpecificationTypeNotPresentException
- if any of the generic superinterfaces refers to a non-existent type declarationMalformedParameterizedTypeException
- if any of the generic superinterfaces refer to a parameterized type that cannot be instantiated for any reason Since: -
getComponentType
public Class<?> getComponentType()Returns theClass
representing the component type of an array. If this class does not represent an array class this method returns null.Returns: the
Class
representing the component type of this class if this class is an array Since:See Also:
Array
-
getModifiers
public int getModifiers()Returns the Java language modifiers for this class or interface, encoded in an integer. The modifiers consist of the Java Virtual Machine's constants for
public
,protected
,private
,final
,static
,abstract
andinterface
; they should be decoded using the methods of classModifier
.If the underlying class is an array class, then its
public
,private
andprotected
modifiers are the same as those of its component type. If thisClass
object represents a primitive type or void, itspublic
modifier is alwaystrue
, and itsprotected
andprivate
modifiers are alwaysfalse
. If thisClass
object represents an array class, a primitive type or void, then itsfinal
modifier is alwaystrue
and its interface modifier is alwaysfalse
. The values of its other modifiers are not determined by this specification.The modifier encodings are defined in section 4.1 of The Java Virtual Machine Specification.
Returns: the
int
representing the modifiers for this class Since:See Also:
Modifier
-
getSigners
public Object[] getSigners()Gets the signers of this class.Returns: the signers of this class, or null if there are no signers. In particular, this method returns null if this
Class
object represents a primitive type or void. Since: -
getEnclosingMethod
public Method getEnclosingMethod() throws SecurityExceptionIf this
Class
object represents a local or anonymous class within a method, returns aMethod
object representing the immediately enclosing method of the underlying class. Returnsnull
otherwise.In particular, this method returns
null
if the underlying class is a local or anonymous class immediately enclosed by a type declaration, instance initializer or static initializer.Returns: the immediately enclosing method of the underlying class, if that class is a local or anonymous class; otherwise
null
. Throws:SecurityException
- If a security manager, s, is present and any of the following conditions is met:the caller's class loader is not the same as the class loader of the enclosing class and invocation of
s.checkPermission
method withRuntimePermission("accessDeclaredMembers")
denies access to the methods within the enclosing classthe caller's class loader is not the same as or an ancestor of the class loader for the enclosing class and invocation of
s.checkPackageAccess()
denies access to the package of the enclosing class
Since:
-
getEnclosingConstructor
public Constructor<?> getEnclosingConstructor() throws SecurityExceptionIf thisClass
object represents a local or anonymous class within a constructor, returns aConstructor
object representing the immediately enclosing constructor of the underlying class. Returnsnull
otherwise. In particular, this method returnsnull
if the underlying class is a local or anonymous class immediately enclosed by a type declaration, instance initializer or static initializer.Returns: the immediately enclosing constructor of the underlying class, if that class is a local or anonymous class; otherwise
null
. Throws:SecurityException
- If a security manager, s, is present and any of the following conditions is met:the caller's class loader is not the same as the class loader of the enclosing class and invocation of
s.checkPermission
method withRuntimePermission("accessDeclaredMembers")
denies access to the constructors within the enclosing classthe caller's class loader is not the same as or an ancestor of the class loader for the enclosing class and invocation of
s.checkPackageAccess()
denies access to the package of the enclosing class
Since:
-
getDeclaringClass
public Class<?> getDeclaringClass() throws SecurityExceptionIf the class or interface represented by thisClass
object is a member of another class, returns theClass
object representing the class in which it was declared. This method returns null if this class or interface is not a member of any other class. If thisClass
object represents an array class, a primitive type, or void,then this method returns null.Returns: the declaring class for this class Throws:
SecurityException
- If a security manager, s, is present and the caller's class loader is not the same as or an ancestor of the class loader for the declaring class and invocation ofs.checkPackageAccess()
denies access to the package of the declaring class Since: -
getEnclosingClass
public Class<?> getEnclosingClass() throws SecurityExceptionReturns the immediately enclosing class of the underlying class. If the underlying class is a top level class this method returnsnull
.Returns: the immediately enclosing class of the underlying class Throws:
SecurityException
- If a security manager, s, is present and the caller's class loader is not the same as or an ancestor of the class loader for the enclosing class and invocation ofs.checkPackageAccess()
denies access to the package of the enclosing class Since: -
getSimpleName
public String getSimpleName()Returns the simple name of the underlying class as given in the source code. Returns an empty string if the underlying class is anonymous.
The simple name of an array is the simple name of the component type with "[]" appended. In particular the simple name of an array whose component type is anonymous is "[]".
Returns: the simple name of the underlying class Since:
-
getTypeName
public String getTypeName()Return an informative string for the name of this type.Specified by:
getTypeName
in interfaceType
Returns: an informative string for the name of this type Since: -
getCanonicalName
public String getCanonicalName()Returns the canonical name of the underlying class as defined by The Java Language Specification. Returnsnull
if the underlying class does not have a canonical name. Classes without canonical names include:- a local class
- a anonymous class
- a hidden class
- an array whose component type does not have a canonical name
Returns: the canonical name of the underlying class if it exists, and
null
otherwise. Since: -
isAnonymousClass
public boolean isAnonymousClass()Returnstrue
if and only if the underlying class is an anonymous class.API Note: An anonymous class is not a hidden class. Returns:
true
if and only if this class is an anonymous class. Since: -
isLocalClass
public boolean isLocalClass()Returnstrue
if and only if the underlying class is a local class.Returns:
true
if and only if this class is a local class. Since: -
isMemberClass
public boolean isMemberClass()Returnstrue
if and only if the underlying class is a member class.Returns:
true
if and only if this class is a member class. Since: -
getClasses
public Class<?>[] getClasses()Returns an array containingClass
objects representing all the public classes and interfaces that are members of the class represented by thisClass
object. This includes public class and interface members inherited from superclasses and public class and interface members declared by the class. This method returns an array of length 0 if thisClass
object has no public member classes or interfaces. This method also returns an array of length 0 if thisClass
object represents a primitive type, an array class, or void.Returns: the array of
Class
objects representing the public members of this class Throws:SecurityException
- If a security manager, s, is present and the caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation ofs.checkPackageAccess()
denies access to the package of this class. Since: -
getFields
public Field[] getFields() throws SecurityExceptionReturns an array containing
Field
objects reflecting all the accessible public fields of the class or interface represented by thisClass
object.If this
Class
object represents a class or interface with no accessible public fields, then this method returns an array of length 0.If this
Class
object represents a class, then this method returns the public fields of the class and of all its superclasses and superinterfaces.If this
Class
object represents an interface, then this method returns the fields of the interface and of all its superinterfaces.If this
Class
object represents an array type, a primitive type, or void, then this method returns an array of length 0.The elements in the returned array are not sorted and are not in any particular order.
Returns: the array of
Field
objects representing the public fields Throws:SecurityException
- If a security manager, s, is present and the caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation ofs.checkPackageAccess()
denies access to the package of this class. See Java Language Specification: -
getMethods
public Method[] getMethods() throws SecurityExceptionReturns an array containing
Method
objects reflecting all the public methods of the class or interface represented by thisClass
object, including those declared by the class or interface and those inherited from superclasses and superinterfaces.If this
Class
object represents an array type, then the returned array has aMethod
object for each of the public methods inherited by the array type fromObject
. It does not contain aMethod
object forclone()
.If this
Class
object represents an interface then the returned array does not contain any implicitly declared methods fromObject
. Therefore, if no methods are explicitly declared in this interface or any of its superinterfaces then the returned array has length 0. (Note that aClass
object which represents a class always has public methods, inherited fromObject
.)The returned array never contains methods with names "
<init>
" or "<clinit>
".The elements in the returned array are not sorted and are not in any particular order.
Generally, the result is computed as with the following 4 step algorithm. Let C be the class or interface represented by this
Class
object:- A union of methods is composed of:
- C's declared public instance and static methods as returned by
getDeclaredMethods()
and filtered to include only public methods. - If C is a class other than
Object
, then include the result of invoking this algorithm recursively on the superclass of C. - Include the results of invoking this algorithm recursively on all direct superinterfaces of C, but include only instance methods.
- C's declared public instance and static methods as returned by
- Union from step 1 is partitioned into subsets of methods with same signature (name, parameter types) and return type.
- Within each such subset only the most specific methods are selected.
Let method M be a method from a set of methods with same signature
and return type. M is most specific if there is no such method
N != M from the same set, such that N is more specific than M.
N is more specific than M if:
- N is declared by a class and M is declared by an interface; or
- N and M are both declared by classes or both by interfaces and N's declaring type is the same as or a subtype of M's declaring type (clearly, if M's and N's declaring types are the same type, then M and N are the same method).
- The result of this algorithm is the union of all selected methods from step 3.
API Note: There may be more than one method with a particular name and parameter types in a class because while the Java language forbids a class to declare multiple methods with the same signature but different return types, the Java virtual machine does not. This increased flexibility in the virtual machine can be used to implement various language features. For example, covariant returns can be implemented with bridge methods; the bridge method and the overriding method would have the same signature but different return types. Returns: the array of
Method
objects representing the public methods of this class Throws:SecurityException
- If a security manager, s, is present and the caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation ofs.checkPackageAccess()
denies access to the package of this class. See Java Language Specification: - A union of methods is composed of:
-
getConstructors
public Constructor<?>[] getConstructors() throws SecurityExceptionReturns an array containingConstructor
objects reflecting all the public constructors of the class represented by thisClass
object. An array of length 0 is returned if the class has no public constructors, or if the class is an array class, or if the class reflects a primitive type or void.API Note: While this method returns an array of
Constructor<T>
objects (that is an array of constructors from this class), the return type of this method isConstructor<?>[]
and notConstructor<T>[]
as might be expected. This less informative return type is necessary since after being returned from this method, the array could be modified to holdConstructor
objects for different classes, which would violate the type guarantees ofConstructor<T>[]
. Returns: the array ofConstructor
objects representing the public constructors of this class Throws:SecurityException
- If a security manager, s, is present and the caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation ofs.checkPackageAccess()
denies access to the package of this class. Since: -
getField
Returns a
Field
object that reflects the specified public member field of the class or interface represented by thisClass
object. Thename
parameter is aString
specifying the simple name of the desired field.The field to be reflected is determined by the algorithm that follows. Let C be the class or interface represented by this
Class
object:- If C declares a public field with the name specified, that is the field to be reflected.
- If no field was found in step 1 above, this algorithm is applied recursively to each direct superinterface of C. The direct superinterfaces are searched in the order they were declared.
- If no field was found in steps 1 and 2 above, and C has a
superclass S, then this algorithm is invoked recursively upon S.
If C has no superclass, then a
NoSuchFieldException
is thrown.
If this
Class
object represents an array type, then this method does not find thelength
field of the array type.Parameters:
name
- the field name Returns: theField
object of this class specified byname
Throws:NoSuchFieldException
- if a field with the specified name is not found.NullPointerException
- ifname
isnull
SecurityException
- If a security manager, s, is present and the caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation ofs.checkPackageAccess()
denies access to the package of this class. See Java Language Specification: -
getMethod
Returns a
Method
object that reflects the specified public member method of the class or interface represented by thisClass
object. Thename
parameter is aString
specifying the simple name of the desired method. TheparameterTypes
parameter is an array ofClass
objects that identify the method's formal parameter types, in declared order. IfparameterTypes
isnull
, it is treated as if it were an empty array.If this
Class
object represents an array type, then this method finds any public method inherited by the array type fromObject
except methodclone()
.If this
Class
object represents an interface then this method does not find any implicitly declared method fromObject
. Therefore, if no methods are explicitly declared in this interface or any of its superinterfaces, then this method does not find any method.This method does not find any method with name "
<init>
" or "<clinit>
".Generally, the method to be reflected is determined by the 4 step algorithm that follows. Let C be the class or interface represented by this
Class
object:- A union of methods is composed of:
- C's declared public instance and static methods as returned by
getDeclaredMethods()
and filtered to include only public methods that match givenname
andparameterTypes
- If C is a class other than
Object
, then include the result of invoking this algorithm recursively on the superclass of C. - Include the results of invoking this algorithm recursively on all direct superinterfaces of C, but include only instance methods.
- C's declared public instance and static methods as returned by
- This union is partitioned into subsets of methods with same return type (the selection of methods from step 1 also guarantees that they have the same method name and parameter types).
- Within each such subset only the most specific methods are selected.
Let method M be a method from a set of methods with same VM
signature (return type, name, parameter types).
M is most specific if there is no such method N != M from the same
set, such that N is more specific than M. N is more specific than M
if:
- N is declared by a class and M is declared by an interface; or
- N and M are both declared by classes or both by interfaces and N's declaring type is the same as or a subtype of M's declaring type (clearly, if M's and N's declaring types are the same type, then M and N are the same method).
- The result of this algorithm is chosen arbitrarily from the methods
with most specific return type among all selected methods from step 3.
Let R be a return type of a method M from the set of all selected methods
from step 3. M is a method with most specific return type if there is
no such method N != M from the same set, having return type S != R,
such that S is a subtype of R as determined by
R.class.
isAssignableFrom(java.lang.Class<?>)
(S.class).
API Note: There may be more than one method with matching name and parameter types in a class because while the Java language forbids a class to declare multiple methods with the same signature but different return types, the Java virtual machine does not. This increased flexibility in the virtual machine can be used to implement various language features. For example, covariant returns can be implemented with bridge methods; the bridge method and the overriding method would have the same signature but different return types. This method would return the overriding method as it would have a more specific return type. Parameters:
name
- the name of the methodparameterTypes
- the list of parameters Returns: theMethod
object that matches the specifiedname
andparameterTypes
Throws:NoSuchMethodException
- if a matching method is not found or if the name is "<init>"or "<clinit>".NullPointerException
- ifname
isnull
SecurityException
- If a security manager, s, is present and the caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation ofs.checkPackageAccess()
denies access to the package of this class. See Java Language Specification: - A union of methods is composed of:
-
getConstructor
Returns a
Constructor
object that reflects the specified public constructor of the class represented by thisClass
object. TheparameterTypes
parameter is an array ofClass
objects that identify the constructor's formal parameter types, in declared order.If this
Class
object represents an inner class declared in a non-static context, the formal parameter types include the explicit enclosing instance as the first parameter.The constructor to reflect is the public constructor of the class represented by this
Class
object whose formal parameter types match those specified byparameterTypes
.Parameters:
parameterTypes
- the parameter array Returns: theConstructor
object of the public constructor that matches the specifiedparameterTypes
Throws:NoSuchMethodException
- if a matching method is not found.SecurityException
- If a security manager, s, is present and the caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation ofs.checkPackageAccess()
denies access to the package of this class. Since: -
getDeclaredClasses
public Class<?>[] getDeclaredClasses() throws SecurityExceptionReturns an array ofClass
objects reflecting all the classes and interfaces declared as members of the class represented by thisClass
object. This includes public, protected, default (package) access, and private classes and interfaces declared by the class, but excludes inherited classes and interfaces. This method returns an array of length 0 if the class declares no classes or interfaces as members, or if thisClass
object represents a primitive type, an array class, or void.Returns: the array of
Class
objects representing all the declared members of this class Throws:SecurityException
- If a security manager, s, is present and any of the following conditions is met:the caller's class loader is not the same as the class loader of this class and invocation of
s.checkPermission
method withRuntimePermission("accessDeclaredMembers")
denies access to the declared classes within this classthe caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation of
s.checkPackageAccess()
denies access to the package of this class
Since:
-
getDeclaredFields
public Field[] getDeclaredFields() throws SecurityExceptionReturns an array of
Field
objects reflecting all the fields declared by the class or interface represented by thisClass
object. This includes public, protected, default (package) access, and private fields, but excludes inherited fields.If this
Class
object represents a class or interface with no declared fields, then this method returns an array of length 0.If this
Class
object represents an array type, a primitive type, or void, then this method returns an array of length 0.The elements in the returned array are not sorted and are not in any particular order.
Returns: the array of
Field
objects representing all the declared fields of this class Throws:SecurityException
- If a security manager, s, is present and any of the following conditions is met:the caller's class loader is not the same as the class loader of this class and invocation of
s.checkPermission
method withRuntimePermission("accessDeclaredMembers")
denies access to the declared fields within this classthe caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation of
s.checkPackageAccess()
denies access to the package of this class
See Java Language Specification:
-
getRecordComponents
public RecordComponent[] getRecordComponents()This method is associated with records, a preview feature of the Java language. Preview features may be removed in a future release, or upgraded to permanent features of the Java language.Returns an array of
RecordComponent
objects representing all the record components of this record class, ornull
if this class is not a record class.The components are returned in the same order that they are declared in the record header. The array is empty if this record class has no components. If the class is not a record class, that is
isRecord()
returnsfalse
, then this method returnsnull
. Conversely, ifisRecord()
returnstrue
, then this method returns a non-null value.Returns: An array of
RecordComponent
objects representing all the record components of this record class, ornull
if this class is not a record class Throws:SecurityException
- If a security manager, s, is present and any of the following conditions is met:the caller's class loader is not the same as the class loader of this class and invocation of
s.checkPermission
method withRuntimePermission("accessDeclaredMembers")
denies access to the declared methods within this classthe caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation of
s.checkPackageAccess()
denies access to the package of this class
See Java Language Specification:
8.10 Record Types
Since: -
getDeclaredMethods
public Method[] getDeclaredMethods() throws SecurityExceptionReturns an array containing
Method
objects reflecting all the declared methods of the class or interface represented by thisClass
object, including public, protected, default (package) access, and private methods, but excluding inherited methods.If this
Class
object represents a type that has multiple declared methods with the same name and parameter types, but different return types, then the returned array has aMethod
object for each such method.If this
Class
object represents a type that has a class initialization method<clinit>
, then the returned array does not have a correspondingMethod
object.If this
Class
object represents a class or interface with no declared methods, then the returned array has length 0.If this
Class
object represents an array type, a primitive type, or void, then the returned array has length 0.The elements in the returned array are not sorted and are not in any particular order.
Returns: the array of
Method
objects representing all the declared methods of this class Throws:SecurityException
- If a security manager, s, is present and any of the following conditions is met:the caller's class loader is not the same as the class loader of this class and invocation of
s.checkPermission
method withRuntimePermission("accessDeclaredMembers")
denies access to the declared methods within this classthe caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation of
s.checkPackageAccess()
denies access to the package of this class
See Java Language Specification:
-
getDeclaredConstructors
public Constructor<?>[] getDeclaredConstructors() throws SecurityExceptionReturns an array of
Constructor
objects reflecting all the constructors declared by the class represented by thisClass
object. These are public, protected, default (package) access, and private constructors. The elements in the array returned are not sorted and are not in any particular order. If the class has a default constructor, it is included in the returned array. This method returns an array of length 0 if thisClass
object represents an interface, a primitive type, an array class, or void.See The Java Language Specification, section 8.2.
Returns: the array of
Constructor
objects representing all the declared constructors of this class Throws:SecurityException
- If a security manager, s, is present and any of the following conditions is met:the caller's class loader is not the same as the class loader of this class and invocation of
s.checkPermission
method withRuntimePermission("accessDeclaredMembers")
denies access to the declared constructors within this classthe caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation of
s.checkPackageAccess()
denies access to the package of this class
Since:
-
getDeclaredField
Returns a
Field
object that reflects the specified declared field of the class or interface represented by thisClass
object. Thename
parameter is aString
that specifies the simple name of the desired field.If this
Class
object represents an array type, then this method does not find thelength
field of the array type.Parameters:
name
- the name of the field Returns: theField
object for the specified field in this class Throws:NoSuchFieldException
- if a field with the specified name is not found.NullPointerException
- ifname
isnull
SecurityException
- If a security manager, s, is present and any of the following conditions is met:the caller's class loader is not the same as the class loader of this class and invocation of
s.checkPermission
method withRuntimePermission("accessDeclaredMembers")
denies access to the declared fieldthe caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation of
s.checkPackageAccess()
denies access to the package of this class
See Java Language Specification:
-
getDeclaredMethod
public Method getDeclaredMethod(String name, Class<?>... parameterTypes) throws NoSuchMethodException, SecurityExceptionReturns a
Method
object that reflects the specified declared method of the class or interface represented by thisClass
object. Thename
parameter is aString
that specifies the simple name of the desired method, and theparameterTypes
parameter is an array ofClass
objects that identify the method's formal parameter types, in declared order. If more than one method with the same parameter types is declared in a class, and one of these methods has a return type that is more specific than any of the others, that method is returned; otherwise one of the methods is chosen arbitrarily. If the name is "<init>"or "<clinit>" aNoSuchMethodException
is raised.If this
Class
object represents an array type, then this method does not find theclone()
method.Parameters:
name
- the name of the methodparameterTypes
- the parameter array Returns: theMethod
object for the method of this class matching the specified name and parameters Throws:NoSuchMethodException
- if a matching method is not found.NullPointerException
- ifname
isnull
SecurityException
- If a security manager, s, is present and any of the following conditions is met:the caller's class loader is not the same as the class loader of this class and invocation of
s.checkPermission
method withRuntimePermission("accessDeclaredMembers")
denies access to the declared methodthe caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation of
s.checkPackageAccess()
denies access to the package of this class
See Java Language Specification:
-
getDeclaredConstructor
public Constructor<T> getDeclaredConstructor(Class<?>... parameterTypes) throws NoSuchMethodException, SecurityExceptionReturns a
Constructor
object that reflects the specified constructor of the class or interface represented by thisClass
object. TheparameterTypes
parameter is an array ofClass
objects that identify the constructor's formal parameter types, in declared order.If this
Class
object represents an inner class declared in a non-static context, the formal parameter types include the explicit enclosing instance as the first parameter.Parameters:
parameterTypes
- the parameter array Returns: TheConstructor
object for the constructor with the specified parameter list Throws:NoSuchMethodException
- if a matching method is not found.SecurityException
- If a security manager, s, is present and any of the following conditions is met:the caller's class loader is not the same as the class loader of this class and invocation of
s.checkPermission
method withRuntimePermission("accessDeclaredMembers")
denies access to the declared constructorthe caller's class loader is not the same as or an ancestor of the class loader for the current class and invocation of
s.checkPackageAccess()
denies access to the package of this class
Since:
-
getResourceAsStream
public InputStream getResourceAsStream(String name)Finds a resource with a given name.
If this class is in a named
Module
then this method will attempt to find the resource in the module. This is done by delegating to the module's class loaderfindResource(String,String)
method, invoking it with the module name and the absolute name of the resource. Resources in named modules are subject to the rules for encapsulation specified in theModule
getResourceAsStream
method and so this method returnsnull
when the resource is a non-".class
" resource in a package that is not open to the caller's module.Otherwise, if this class is not in a named module then the rules for searching resources associated with a given class are implemented by the defining class loader of the class. This method delegates to this
Class
object's class loader. If thisClass
object was loaded by the bootstrap class loader, the method delegates toClassLoader.getSystemResourceAsStream(java.lang.String)
.Before delegation, an absolute resource name is constructed from the given resource name using this algorithm:
If the
name
begins with a'/'
('\u002f'
), then the absolute name of the resource is the portion of thename
following the'/'
.Otherwise, the absolute name is of the following form:
modified_package_name/name
Where the
modified_package_name
is the package name of this object with'/'
substituted for'.'
('\u002e'
).
Parameters:
name
- name of the desired resource Returns: AInputStream
object;null
if no resource with this name is found, the resource is in a package that is not open to at least the caller module, or access to the resource is denied by the security manager. Throws:NullPointerException
- Ifname
isnull
Since:See Also:
Module.getResourceAsStream(String)
-
getResource
Finds a resource with a given name.
If this class is in a named
Module
then this method will attempt to find the resource in the module. This is done by delegating to the module's class loaderfindResource(String,String)
method, invoking it with the module name and the absolute name of the resource. Resources in named modules are subject to the rules for encapsulation specified in theModule
getResourceAsStream
method and so this method returnsnull
when the resource is a non-".class
" resource in a package that is not open to the caller's module.Otherwise, if this class is not in a named module then the rules for searching resources associated with a given class are implemented by the defining class loader of the class. This method delegates to this
Class
object's class loader. If thisClass
object was loaded by the bootstrap class loader, the method delegates toClassLoader.getSystemResource(java.lang.String)
.Before delegation, an absolute resource name is constructed from the given resource name using this algorithm:
If the
name
begins with a'/'
('\u002f'
), then the absolute name of the resource is the portion of thename
following the'/'
.Otherwise, the absolute name is of the following form:
modified_package_name/name
Where the
modified_package_name
is the package name of this object with'/'
substituted for'.'
('\u002e'
).
Parameters:
name
- name of the desired resource Returns: AURL
object;null
if no resource with this name is found, the resource cannot be located by a URL, the resource is in a package that is not open to at least the caller module, or access to the resource is denied by the security manager. Throws:NullPointerException
- Ifname
isnull
Since: -
getProtectionDomain
public ProtectionDomain getProtectionDomain()Returns theProtectionDomain
of this class. If there is a security manager installed, this method first calls the security manager'scheckPermission
method with aRuntimePermission("getProtectionDomain")
permission to ensure it's ok to get theProtectionDomain
.Returns: the ProtectionDomain of this class Throws:
SecurityException
- if a security manager exists and itscheckPermission
method doesn't allow getting the ProtectionDomain. Since:See Also:
ProtectionDomain
,SecurityManager.checkPermission(java.security.Permission)
,RuntimePermission
-
desiredAssertionStatus
public boolean desiredAssertionStatus()Returns the assertion status that would be assigned to this class if it were to be initialized at the time this method is invoked. If this class has had its assertion status set, the most recent setting will be returned; otherwise, if any package default assertion status pertains to this class, the most recent setting for the most specific pertinent package default assertion status is returned; otherwise, if this class is not a system class (i.e., it has a class loader) its class loader's default assertion status is returned; otherwise, the system class default assertion status is returned.API Note: Few programmers will have any need for this method; it is provided for the benefit of the JDK itself. (It allows a class to determine at the time that it is initialized whether assertions should be enabled.) Note that this method is not guaranteed to return the actual assertion status that was (or will be) associated with the specified class when it was (or will be) initialized. Returns: the desired assertion status of the specified class. Since:
See Also:
ClassLoader.setClassAssertionStatus(java.lang.String, boolean)
,ClassLoader.setPackageAssertionStatus(java.lang.String, boolean)
,ClassLoader.setDefaultAssertionStatus(boolean)
-
isEnum
public boolean isEnum()Returns true if and only if this class was declared as an enum in the source code.
Note that
Enum
is not itself an enum type.Also note that if an enum constant is declared with a class body, the class of that enum constant object is an anonymous class and not the class of the declaring enum type. The
Enum.getDeclaringClass()
method of an enum constant can be used to get the class of the enum type declaring the constant.Returns: true if and only if this class was declared as an enum in the source code See Java Language Specification:
8.9.1 Enum Constants
Since: -
isRecord
public boolean isRecord()This method is associated with records, a preview feature of the Java language. Preview features may be removed in a future release, or upgraded to permanent features of the Java language.Returns
true
if and only if this class is a record class.The direct superclass of a record class is
java.lang.Record
. A record class has (possibly zero) record components, that is,getRecordComponents()
returns a non-null value.Note that class
Record
is not a record type and thus invoking this method on classRecord
returnsfalse
.Returns: true if and only if this class is a record class, otherwise false See Java Language Specification:
8.10 Record Types
Since: -
getEnumConstants
public T[] getEnumConstants()Returns the elements of this enum class or null if this Class object does not represent an enum type.Returns: an array containing the values comprising the enum class represented by this
Class
object in the order they're declared, or null if thisClass
object does not represent an enum type Since: -
Casts an object to the class or interface represented by this
Class
object.Parameters:
obj
- the object to be cast Returns: the object after casting, or null if obj is null Throws:ClassCastException
- if the object is not null and is not assignable to the type T. Since: -
asSubclass
Casts this
Class
object to represent a subclass of the class represented by the specified class object. Checks that the cast is valid, and throws aClassCastException
if it is not. If this method succeeds, it always returns a reference to thisClass
object.This method is useful when a client needs to "narrow" the type of a
Class
object to pass it to an API that restricts theClass
objects that it is willing to accept. A cast would generate a compile-time warning, as the correctness of the cast could not be checked at runtime (because generic types are implemented by erasure).Type Parameters:
U
- the type to cast thisClass
object to Parameters:clazz
- the class of the type to cast thisClass
object to Returns: thisClass
object, cast to represent a subclass of the specified class object. Throws:ClassCastException
- if thisClass
object does not represent a subclass of the specified class (here "subclass" includes the class itself). Since: -
getAnnotation
public <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.Note that any annotation returned by this method is a declaration annotation.
Specified by:
getAnnotation
in interfaceAnnotatedElement
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: -
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 interfaceAnnotatedElement
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: -
getAnnotationsByType
public <A extends Annotation> A[] getAnnotationsByType(Class<A> 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 interfaceAnnotatedElement
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: -
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 interfaceAnnotatedElement
Returns: annotations present on this element Since: -
getDeclaredAnnotation
public <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.
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 interfaceAnnotatedElement
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: -
getDeclaredAnnotationsByType
public <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. 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 interfaceAnnotatedElement
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: -
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 interfaceAnnotatedElement
Returns: annotations directly present on this element Since: -
getAnnotatedSuperclass
public AnnotatedType getAnnotatedSuperclass()Returns an
AnnotatedType
object that represents the use of a type to specify the superclass of the entity represented by thisClass
object. (The use of type Foo to specify the superclass in '... extends Foo' is distinct from the declaration of type Foo.)If this
Class
object represents a type whose declaration does not explicitly indicate an annotated superclass, then the return value is anAnnotatedType
object representing an element with no annotations.If this
Class
represents either theObject
class, an interface type, an array type, a primitive type, or void, the return value isnull
.Returns: an object representing the superclass Since:
-
getAnnotatedInterfaces
public AnnotatedType[] getAnnotatedInterfaces()Returns an array of
AnnotatedType
objects that represent the use of types to specify superinterfaces of the entity represented by thisClass
object. (The use of type Foo to specify a superinterface in '... implements Foo' is distinct from the declaration of type Foo.)If this
Class
object represents a class, the return value is an array containing objects representing the uses of interface types to specify interfaces implemented by the class. The order of the objects in the array corresponds to the order of the interface types used in the 'implements' clause of the declaration of thisClass
object.If this
Class
object represents an interface, the return value is an array containing objects representing the uses of interface types to specify interfaces directly extended by the interface. The order of the objects in the array corresponds to the order of the interface types used in the 'extends' clause of the declaration of thisClass
object.If this
Class
object represents a class or interface whose declaration does not explicitly indicate any annotated superinterfaces, the return value is an array of length 0.If this
Class
object represents either theObject
class, an array type, a primitive type, or void, the return value is an array of length 0.Returns: an array representing the superinterfaces Since:
-
getNestHost
public Class<?> getNestHost()Returns the nest host of the nest to which the class or interface represented by this
Class
object belongs. Every class and interface belongs to exactly one nest.If the nest host of this class or interface has previously been determined, then this method returns the nest host. If the nest host of this class or interface has not previously been determined, then this method determines the nest host using the algorithm of JVMS 5.4.4, and returns it.
Often, a class or interface belongs to a nest consisting only of itself, in which case this method returns
this
to indicate that the class or interface is the nest host.If this
Class
object represents a primitive type, an array type, orvoid
, then this method returnsthis
, indicating that the represented entity belongs to the nest consisting only of itself, and is the nest host.Returns: the nest host of this class or interface Throws:
SecurityException
- If the returned class is not the current class, and if a security manager, s, is present and the caller's class loader is not the same as or an ancestor of the class loader for the returned class and invocation ofs.checkPackageAccess()
denies access to the package of the returned class See Java Virtual Machine Specification:4.7.28 The
NestHost
Attribute
4.7.29 TheNestMembers
Attribute
5.4.4 Access Control
Since: -
isNestmateOf
public boolean isNestmateOf(Class<?> c)Determines if the givenClass
is a nestmate of the class or interface represented by thisClass
object. Two classes or interfaces are nestmates if they have the same nest host.Parameters:
c
- the class to check Returns:true
if this class andc
are members of the same nest; andfalse
otherwise. Since: -
getNestMembers
public Class<?>[] getNestMembers()Returns an array containing
Class
objects representing all the classes and interfaces that are members of the nest to which the class or interface represented by thisClass
object belongs.First, this method obtains the nest host,
H
, of the nest to which the class or interface represented by thisClass
object belongs. The zeroth element of the returned array isH
.Then, for each class or interface
C
which is recorded byH
as being a member of its nest, this method attempts to obtain theClass
object forC
(using the defining class loader of the currentClass
object), and then obtains the nest host of the nest to whichC
belongs. The classes and interfaces which are recorded byH
as being members of its nest, and for whichH
can be determined as their nest host, are indicated by subsequent elements of the returned array. The order of such elements is unspecified. Duplicates are permitted.If this
Class
object represents a primitive type, an array type, orvoid
, then this method returns a single-element array containingthis
.API Note: The returned array includes only the nest members recorded in the
NestMembers
attribute, and not any hidden classes that were added to the nest viaLookup::defineHiddenClass
. Returns: an array of all classes and interfaces in the same nest as this class or interface Throws:SecurityException
- If any returned class is not the current class, and if a security manager, s, is present and the caller's class loader is not the same as or an ancestor of the class loader for that returned class and invocation ofs.checkPackageAccess()
denies access to the package of that returned class See Java Virtual Machine Specification:4.7.28 The
NestHost
Attribute
4.7.29 TheNestMembers
Attribute
Since:See Also:
getNestHost()
-
descriptorString
public String descriptorString()Returns the descriptor string of the entity (class, interface, array class, primitive type, or
void
) represented by thisClass
object.If this
Class
object represents a class or interface, not an array class, then:- If the class or interface is not hidden,
then the result is a field descriptor (JVMS 4.3.2)
for the class or interface. Calling
ClassDesc::ofDescriptor
with the result descriptor string produces aClassDesc
describing this class or interface. - If the class or interface is hidden,
then the result is a string of the form:
"L" +
N+ "." + <suffix> + ";"
class
file passed toLookup::defineHiddenClass
, and<suffix>
is an unqualified name. A hidden class or interface has no nominal descriptor. The result string is not a type descriptor.
If this
Class
object represents an array class, then the result is a string consisting of one or more '[
' characters representing the depth of the array nesting, followed by the descriptor string of the element type.- If the element type is not a hidden class
or interface, then this array class can be described nominally.
Calling
ClassDesc::ofDescriptor
with the result descriptor string produces aClassDesc
describing this array class. - If the element type is a hidden class or interface, then this array class cannot be described nominally. The result string is not a type descriptor.
If this
Class
object represents a primitive type orvoid
, then the result is a field descriptor string which is a one-letter code corresponding to a primitive type orvoid
("B", "C", "D", "F", "I", "J", "S", "Z", "V"
) (JVMS 4.3.2).Specified by:
descriptorString
in interfaceTypeDescriptor
API Note: This is not a strict inverse offorName(java.lang.String)
; distinct classes which share a common name but have different class loaders will have identical descriptor strings. Returns: the descriptor string for thisClass
object See Java Virtual Machine Specification:4.3.2 Field Descriptors
Since: - If the class or interface is not hidden,
then the result is a field descriptor (JVMS 4.3.2)
for the class or interface. Calling
-
componentType
public Class<?> componentType()Returns the component type of thisClass
, if it describes an array type, ornull
otherwise.Specified by:
componentType
in interfaceTypeDescriptor.OfField<T>
Implementation Requirements: Equivalent togetComponentType()
. Returns: aClass
describing the component type, ornull
if thisClass
does not describe an array type Since: -
arrayType
public Class<?> arrayType()Returns aClass
for an array type whose component type is described by this Class.Specified by:
arrayType
in interfaceTypeDescriptor.OfField<T>
Returns: aClass
describing the array type Since: -
describeConstable
Returns a nominal descriptor for this instance, if one can be constructed, or an emptyOptional
if one cannot be.Specified by:
describeConstable
in interfaceConstable
Returns: AnOptional
containing the resulting nominal descriptor, or an emptyOptional
if one cannot be constructed. Since: -
isHidden
public boolean isHidden()Returnstrue
if and only if the underlying class is a hidden class.Returns:
true
if and only if this class is a hidden class. Since: -
permittedSubclasses
public ClassDesc[] permittedSubclasses()This method is associated with sealed classes, a preview feature of the Java language. Preview features may be removed in a future release, or upgraded to permanent features of the Java language.Returns an array containing
ClassDesc
objects representing all the direct subclasses or direct implementation classes permitted to extend or implement this class or interface if it is sealed. The order of such elements is unspecified. If thisClass
object represents a primitive type,void
, an array type, or a class or interface that is not sealed, an empty array is returned.Returns: an array of class descriptors of all the permitted subclasses of this class or interface See Java Language Specification:
-
isSealed
public boolean isSealed()*This method is associated with sealed classes, a preview feature of the Java language. Preview features may be removed in a future release, or upgraded to permanent features of the Java language.Returns
true
if and only if thisClass
object represents a sealed class or interface. If thisClass
object represents a primitive type,void
, or an array type, this method returnsfalse
.Returns:
true
if and only if thisClass
object represents a sealed class or interface. See Java Language Specification:
-
Report a bug or suggest an enhancement
For further API reference and developer documentation see the Java SE Documentation, which contains more detailed, developer-targeted descriptions with conceptual overviews, definitions of terms, workarounds, and working code examples.
Java is a trademark or registered trademark of Oracle and/or its affiliates in the US and other countries.
Copyright © 1993, 2020, Oracle and/or its affiliates, 500 Oracle Parkway, Redwood Shores, CA 94065 USA.
All rights reserved. Use is subject to license terms and the documentation redistribution policy. Modify . Modify Ad Choices.
Recommend
About Joyk
Aggregate valuable and interesting links.
Joyk means Joy of geeK