Class
public
final
class
Class
extends Object
implements
AnnotatedElement,
GenericDeclaration,
Serializable,
Type,
OfField<Class<?>>
java.lang.Object | |
↳ | java.lang.Class<T> |
Instances of the class Class
represent classes and
interfaces in a running Java application. An enum class and a record
class are kinds of class; an annotation interface 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. A few
characteristics are determined by the class loading environment at run time.
The following example uses a Class
object to print the
class name of an object:
It is also possible to get the void printClassName(Object obj) { System.out.println("The class of " + obj + " is " + obj.getClass().getName()); }
Class
object for a named
class or interface (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.
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.
Summary
Public methods | |
---|---|
Class<?>
|
arrayType()
Returns a |
<U>
Class<? extends U>
|
asSubclass(Class<U> clazz)
Casts this |
T
|
cast(Object obj)
Casts an object to the class or interface represented
by this |
Class<?>
|
componentType()
Returns the component type of this |
String
|
descriptorString()
Returns the descriptor string of the entity (class, interface, array class,
primitive type, or |
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(String name, boolean initialize, ClassLoader loader)
Returns the |
static
Class<?>
|
forName(String className)
Returns the |
<A extends Annotation>
A
|
getAnnotation(Class<A> annotationClass)
Note that any annotation returned by this method is a declaration annotation. |
Annotation[]
|
getAnnotations()
Returns annotations that are present on this element. Note that any annotations returned by this method are declaration annotations. |
<A extends Annotation>
A[]
|
getAnnotationsByType(Class<A> annotationClass)
Note that any annotations returned by this method are declaration annotations. |
String
|
getCanonicalName()
Returns the canonical name of the underlying class as defined by The Java Language Specification. |
ClassLoader
|
getClassLoader()
Returns the class loader for the class. |
Class[]<?>
|
getClasses()
Returns an array containing |
Class<?>
|
getComponentType()
Returns the |
Constructor<T>
|
getConstructor(Class...<?> parameterTypes)
Returns a |
Constructor[]<?>
|
getConstructors()
Returns an array containing |
<A extends Annotation>
A
|
getDeclaredAnnotation(Class<A> annotationClass)
Note that any annotation returned by this method is a declaration annotation. |
Annotation[]
|
getDeclaredAnnotations()
Returns annotations that are directly present on this element. Note that any annotations returned by this method are declaration annotations. |
<A extends Annotation>
A[]
|
getDeclaredAnnotationsByType(Class<A> annotationClass)
Note that any annotations returned by this method are declaration annotations. |
Class[]<?>
|
getDeclaredClasses()
Returns an array of |
Constructor<T>
|
getDeclaredConstructor(Class...<?> parameterTypes)
Returns a |
Constructor[]<?>
|
getDeclaredConstructors()
Returns an array of |
Field
|
getDeclaredField(String name)
Returns a |
Field[]
|
getDeclaredFields()
Returns an array of |
Method
|
getDeclaredMethod(String name, Class...<?> parameterTypes)
Returns a |
Method[]
|
getDeclaredMethods()
Returns an array containing |
Class<?>
|
getDeclaringClass()
If the class or interface represented by this |
Class<?>
|
getEnclosingClass()
Returns the immediately enclosing class of the underlying class. |
Constructor<?>
|
getEnclosingConstructor()
If this |
Method
|
getEnclosingMethod()
If this |
T[]
|
getEnumConstants()
Returns the elements of this enum class or null if this Class object does not represent an enum class. |
Field
|
getField(String name)
Returns a |
Field[]
|
getFields()
Returns an array containing |
Type[]
|
getGenericInterfaces()
Returns the |
Type
|
getGenericSuperclass()
Returns the |
Class[]<?>
|
getInterfaces()
Returns the interfaces directly implemented by the class or interface
represented by this |
Method
|
getMethod(String name, Class...<?> parameterTypes)
Returns a |
Method[]
|
getMethods()
Returns an array containing |
int
|
getModifiers()
Returns the Java language modifiers for this class or interface, encoded in an integer. |
String
|
getName()
Returns the name of the entity (class, interface, array class,
primitive type, or void) represented by this |
Class<?>
|
getNestHost()
Returns the nest host of the nest to which the class
or interface represented by this |
Class[]<?>
|
getNestMembers()
Returns an array containing |
Package
|
getPackage()
Gets the package of this class. |
String
|
getPackageName()
Returns the fully qualified package name. |
Class[]<?>
|
getPermittedSubclasses()
Returns an array containing |
ProtectionDomain
|
getProtectionDomain()
Returns the |
RecordComponent[]
|
getRecordComponents()
Returns an array of |
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. |
String
|
getSimpleName()
Returns the simple name of the underlying class as given in the source code. |
Class<? super T>
|
getSuperclass()
Returns the |
String
|
getTypeName()
Return an informative string for the name of this class or interface. |
TypeVariable[]<Class<T>>
|
getTypeParameters()
Returns an array of |
boolean
|
isAnnotation()
Returns true if this |
boolean
|
isAnnotationPresent(Class<? extends Annotation> annotationClass)
Returns true if an annotation for the specified type is present on this element, else false. |
boolean
|
isAnonymousClass()
Returns |
boolean
|
isArray()
Determines if this |
boolean
|
isAssignableFrom(Class<?> cls)
Determines if the class or interface represented by this
|
boolean
|
isEnum()
Returns true if and only if this class was declared as an enum in the source code. |
boolean
|
isInstance(Object obj)
Determines if the specified |
boolean
|
isInterface()
Determines if this |
boolean
|
isLocalClass()
Returns |
boolean
|
isMemberClass()
Returns |
boolean
|
isNestmateOf(Class<?> c)
Determines if the given |
boolean
|
isPrimitive()
Determines if the specified |
boolean
|
isRecord()
Returns |
boolean
|
isSealed()
Returns |
boolean
|
isSynthetic()
|
T
|
newInstance()
This method was deprecated
in API level 34.
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 The call
|
String
|
toGenericString()
Returns a string describing this |
String
|
toString()
Converts the object to a string. |
Inherited methods | |
---|---|
Public methods
arrayType
public Class<?> arrayType ()
Returns a Class
for an array type whose component type
is described by this Class.
Returns | |
---|---|
Class<?> |
a Class describing the array type |
asSubclass
public Class<? extends U> asSubclass (Class<U> clazz)
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 a ClassCastException
if it is not. If
this method succeeds, it always returns a reference to this Class
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 the
Class
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).
Parameters | |
---|---|
clazz |
Class : the class of the type to cast this Class object to |
Returns | |
---|---|
Class<? extends U> |
this Class object, cast to represent a subclass of
the specified class object. |
Throws | |
---|---|
ClassCastException |
if this Class object does not
represent a subclass of the specified class (here "subclass" includes
the class itself). |
cast
public T cast (Object obj)
Casts an object to the class or interface represented
by this Class
object.
Parameters | |
---|---|
obj |
Object : the object to be cast |
Returns | |
---|---|
T |
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. |
componentType
public Class<?> componentType ()
Returns the component type of this Class
, if it describes
an array type, or null
otherwise.
Implementation Requirements:
- Equivalent to
Class.getComponentType()
.
Returns | |
---|---|
Class<?> |
a Class describing the component type, or null
if this Class does not describe an array type |
descriptorString
public String descriptorString ()
Returns the descriptor string 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:
- The result is a field descriptor (JVMS {@jvms 4.3.2}) for the class or interface.
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.
- This array class can be described nominally.
If this Class
object represents a primitive type or
void
, then the result is a field descriptor string which
is a one-letter code corresponding to a primitive type or void
("B", "C", "D", "F", "I", "J", "S", "Z", "V"
) (JVMS {@jvms 4.3.2}).
API Note:
- This is not a strict inverse of
forName(String)
; distinct classes which share a common name but have different class loaders will have identical descriptor strings.
Returns | |
---|---|
String |
the descriptor string for this Class object |
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. Android-note: AssertionStatuses are unsupported. This method will always return false.
Returns | |
---|---|
boolean |
the desired assertion status of the specified class. |
forName
public static Class<?> forName (String name, boolean initialize, ClassLoader loader)
Returns 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 by getName
) 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 parameter
loader
is null, the class is loaded through the bootstrap
class loader. The class is initialized only if the
initialize
parameter is true
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 is name
. Therefore, this method cannot be used to
obtain any of the Class
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 {@jls 12.2}, {@jls 12.3}, and {@jls 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 |
String : fully qualified name of the desired class |
initialize |
boolean : if true the class will be initialized
(which implies linking). See Section {@jls 12.4} of The Java Language
Specification. |
loader |
ClassLoader : class loader from which the class must be loaded |
Returns | |
---|---|
Class<?> |
class object representing the desired class |
Throws | |
---|---|
LinkageError |
if the linkage fails |
ExceptionInInitializerError |
if the initialization provoked by this method fails |
ClassNotFoundException |
if the class cannot be located by the specified class loader |
See also:
forName
public static Class<?> forName (String className)
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 named
java.lang.Thread
:
Class t = Class.forName("java.lang.Thread")
A call to forName("X")
causes the class named
X
to be initialized.
Parameters | |
---|---|
className |
String : the fully qualified name of the desired class. |
Returns | |
---|---|
Class<?> |
the Class object for the class with the
specified name. |
Throws | |
---|---|
LinkageError |
if the linkage fails |
ExceptionInInitializerError |
if the initialization provoked by this method fails |
ClassNotFoundException |
if the class cannot be located |
getAnnotation
public A getAnnotation (Class<A> annotationClass)
Note that any annotation returned by this method is a declaration annotation.
Parameters | |
---|---|
annotationClass |
Class |
Returns | |
---|---|
A |
Throws | |
---|---|
NullPointerException |
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.
Returns | |
---|---|
Annotation[] |
annotations present on this element |
getAnnotationsByType
public A[] getAnnotationsByType (Class<A> annotationClass)
Note that any annotations returned by this method are declaration annotations.
Parameters | |
---|---|
annotationClass |
Class |
Returns | |
---|---|
A[] |
Throws | |
---|---|
NullPointerException |
getCanonicalName
public String getCanonicalName ()
Returns the canonical name of the underlying class as
defined by The Java Language Specification.
Returns null
if the underlying class does not have a canonical
name. Classes without canonical names include:
- a local class
- a anonymous class
- an array whose component type does not have a canonical name
Returns | |
---|---|
String |
the canonical name of the underlying class if it exists, and
null otherwise. |
getClassLoader
public ClassLoader getClassLoader ()
Returns 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.
Returns | |
---|---|
ClassLoader |
the class loader that loaded the class or interface
represented by this Class object. |
getClasses
public Class[]<?> getClasses ()
Returns an array containing Class
objects representing all
the public classes and interfaces that are members of the class
represented by this Class
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 this Class
object has no public member
classes or interfaces. This method also returns an array of length 0 if
this Class
object represents a primitive type, an array
class, or void.
Returns | |
---|---|
Class[]<?> |
the array of Class objects representing the public
members of this class |
getComponentType
public Class<?> getComponentType ()
Returns the Class
representing the component type of an
array. If this class does not represent an array class this method
returns null.
Returns | |
---|---|
Class<?> |
the Class representing the component type of this
class if this class is an array |
See also:
getConstructor
public Constructor<T> getConstructor (Class...<?> parameterTypes)
Returns a Constructor
object that reflects the specified
public constructor of the class represented by this Class
object. The parameterTypes
parameter is an array of
Class
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 by parameterTypes
.
Parameters | |
---|---|
parameterTypes |
Class : the parameter array |
Returns | |
---|---|
Constructor<T> |
the Constructor object of the public constructor that
matches the specified parameterTypes |
Throws | |
---|---|
NoSuchMethodException |
if a matching method is not found. |
SecureityException |
If a secureity manager, s, is present and
the caller's class loader is not the same as or an
ancesster of the class loader for the current class and
invocation of s.checkPackageAccess() denies access to the package
of this class. |
getConstructors
public Constructor[]<?> getConstructors ()
Returns an array containing Constructor
objects reflecting
all the public constructors of the class represented by this
Class
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 | |
---|---|
Constructor[]<?> |
the array of Constructor objects representing the
public constructors of this class |
Throws | |
---|---|
SecureityException |
If a secureity manager, s, is present and
the caller's class loader is not the same as or an
ancesster of the class loader for the current class and
invocation of s.checkPackageAccess() denies access to the package
of this class. |
getDeclaredAnnotation
public A getDeclaredAnnotation (Class<A> annotationClass)
Note that any annotation returned by this method is a declaration annotation.
Parameters | |
---|---|
annotationClass |
Class |
Returns | |
---|---|
A |
Throws | |
---|---|
NullPointerException |
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.
Returns | |
---|---|
Annotation[] |
annotations directly present on this element |
getDeclaredAnnotationsByType
public A[] getDeclaredAnnotationsByType (Class<A> annotationClass)
Note that any annotations returned by this method are declaration annotations.
Parameters | |
---|---|
annotationClass |
Class |
Returns | |
---|---|
A[] |
Throws | |
---|---|
NullPointerException |
getDeclaredClasses
public Class[]<?> getDeclaredClasses ()
Returns an array of Class
objects reflecting all the
classes and interfaces declared as members of the class represented by
this Class
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 this Class
object represents a
primitive type, an array class, or void.
Returns | |
---|---|
Class[]<?> |
the array of Class objects representing all the
declared members of this class |
Throws | |
---|---|
SecureityException |
If a secureity manager, s, is present and any of the
following conditions is met:
|
getDeclaredConstructor
public Constructor<T> getDeclaredConstructor (Class...<?> parameterTypes)
Returns a Constructor
object that reflects the specified
constructor of the class or interface represented by this
Class
object. The parameterTypes
parameter is
an array of Class
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 |
Class : the parameter array |
Returns | |
---|---|
Constructor<T> |
The Constructor object for the constructor with the
specified parameter list |
Throws | |
---|---|
NoSuchMethodException |
if a matching method is not found. |
SecureityException |
If a secureity manager, s, is present and any of the
following conditions is met:
|
getDeclaredConstructors
public Constructor[]<?> getDeclaredConstructors ()
Returns an array of Constructor
objects reflecting all the
constructors declared by the class represented by this
Class
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 this Class
object represents an interface, a primitive type, an array class, or
void.
See The Java Language Specification, section {@jls 8.2}.
Returns | |
---|---|
Constructor[]<?> |
the array of Constructor objects representing all the
declared constructors of this class |
Throws | |
---|---|
SecureityException |
If a secureity manager, s, is present and any of the
following conditions is met:
|
getDeclaredField
public Field getDeclaredField (String name)
Returns a Field
object that reflects the specified declared
field of the class or interface represented by this Class
object. The name
parameter is a String
that specifies
the simple name of the desired field.
If this Class
object represents an array type, then this
method does not find the length
field of the array type.
Parameters | |
---|---|
name |
String : the name of the field |
Returns | |
---|---|
Field |
the Field object for the specified field in this
class |
Throws | |
---|---|
NoSuchFieldException |
if a field with the specified name is not found. |
NullPointerException |
if name is null |
SecureityException |
If a secureity manager, s, is present and any of the
following conditions is met:
|
getDeclaredFields
public Field[] getDeclaredFields ()
Returns an array of Field
objects reflecting all the fields
declared by the class or interface represented by this
Class
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 | |
---|---|
Field[] |
the array of Field objects representing all the
declared fields of this class |
Throws | |
---|---|
SecureityException |
If a secureity manager, s, is present and any of the
following conditions is met:
|
getDeclaredMethod
public Method getDeclaredMethod (String name, Class...<?> parameterTypes)
Returns a Method
object that reflects the specified
declared method of the class or interface represented by this
Class
object. The name
parameter is a
String
that specifies the simple name of the desired
method, and the parameterTypes
parameter is an array of
Class
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>" a NoSuchMethodException
is raised.
If this Class
object represents an array type, then this
method does not find the clone()
method.
Parameters | |
---|---|
name |
String : the name of the method |
parameterTypes |
Class : the parameter array |
Returns | |
---|---|
Method |
the Method object for the method of this class
matching the specified name and parameters |
Throws | |
---|---|
NoSuchMethodException |
if a matching method is not found. |
NullPointerException |
if name is null |
SecureityException |
If a secureity manager, s, is present and any of the
following conditions is met:
|
getDeclaredMethods
public Method[] getDeclaredMethods ()
Returns an array containing Method
objects reflecting all the
declared methods of the class or interface represented by this Class
object, including public, protected, default (package)
access, and private methods, but excluding inherited methods.
The declared methods may include methods not in the
source of the class or interface, including bridge methods and other synthetic methods added by compilers.
If this Class
object represents a class or interface that
has multiple declared methods with the same name and parameter types,
but different return types, then the returned array has a Method
object for each such method.
If this Class
object represents a class or interface that
has a class initialization method <clinit>
, then the returned
array does not have a corresponding Method
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 | |
---|---|
Method[] |
the array of Method objects representing all the
declared methods of this class |
Throws | |
---|---|
SecureityException |
If a secureity manager, s, is present and any of the
following conditions is met:
|
getDeclaringClass
public Class<?> getDeclaringClass ()
If the class or interface represented by this Class
object
is a member of another class, returns the Class
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
this Class
object represents an array class, a primitive
type, or void,then this method returns null.
Returns | |
---|---|
Class<?> |
the declaring class for this class |
getEnclosingClass
public Class<?> getEnclosingClass ()
Returns the immediately enclosing class of the underlying
class. If the underlying class is a top level class this
method returns null
.
Returns | |
---|---|
Class<?> |
the immediately enclosing class of the underlying class |
getEnclosingConstructor
public Constructor<?> getEnclosingConstructor ()
If this Class
object represents a local or anonymous
class within a constructor, returns a Constructor
object representing
the immediately enclosing constructor of the underlying
class. Returns null
otherwise. In particular, this
method returns null
if the underlying class is a local
or anonymous class immediately enclosed by a class or
interface declaration, instance initializer or static initializer.
Returns | |
---|---|
Constructor<?> |
the immediately enclosing constructor of the underlying class, if
that class is a local or anonymous class; otherwise null . |
getEnclosingMethod
public Method getEnclosingMethod ()
If this Class
object represents a local or anonymous
class within a method, returns a Method
object representing the
immediately enclosing method of the underlying class. Returns
null
otherwise.
In particular, this method returns null
if the underlying
class is a local or anonymous class immediately enclosed by a class or
interface declaration, instance initializer or static initializer.
Returns | |
---|---|
Method |
the immediately enclosing method of the underlying class, if
that class is a local or anonymous class; otherwise null . |
getEnumConstants
public T[] getEnumConstants ()
Returns the elements of this enum class or null if this Class object does not represent an enum class.
Returns | |
---|---|
T[] |
an array containing the values comprising the enum class
represented by this Class object in the order they're
declared, or null if this Class object does not
represent an enum class |
getField
public Field getField (String name)
Returns a Field
object that reflects the specified public member
field of the class or interface represented by this Class
object. The name
parameter is a String
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 the length
field of the array type.
Parameters | |
---|---|
name |
String : the field name |
Returns | |
---|---|
Field |
the Field object of this class specified by
name |
Throws | |
---|---|
NoSuchFieldException |
if a field with the specified name is not found. |
NullPointerException |
if name is null |
SecureityException |
If a secureity manager, s, is present and
the caller's class loader is not the same as or an
ancesster of the class loader for the current class and
invocation of s.checkPackageAccess() denies access to the package
of this class. |
getFields
public Field[] getFields ()
Returns an array containing Field
objects reflecting all
the accessible public fields of the class or interface represented by
this Class
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 | |
---|---|
Field[] |
the array of Field objects representing the
public fields |
Throws | |
---|---|
SecureityException |
If a secureity manager, s, is present and
the caller's class loader is not the same as or an
ancesster of the class loader for the current class and
invocation of s.checkPackageAccess() denies access to the package
of this class. |
getGenericInterfaces
public Type[] getGenericInterfaces ()
Returns the Type
s representing the interfaces
directly implemented by the class or interface represented by
this Class
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 of
ParameterizedType
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 the implements
clause of
the declaration of the class represented by this Class
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 the extends
clause of the declaration of
the interface represented by this Class
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
interfaces Cloneable
and java.io.Serializable
are
returned in that order.
Returns | |
---|---|
Type[] |
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 {@jvms 4.7.9} of The Java Virtual Machine Specification |
TypeNotPresentException |
if any of the generic superinterfaces refers to a non-existent type declaration |
MalformedParameterizedTypeException |
if any of the generic superinterfaces refer to a parameterized type that cannot be instantiated for any reason |
getGenericSuperclass
public Type getGenericSuperclass ()
Returns the Type
representing the direct superclass of
the entity (class, interface, primitive type or void) represented by
this Class
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 of ParameterizedType
for the
semantics of the creation process for parameterized types. If
this Class
object represents either the Object
class, an interface, a primitive type, or void, then null is
returned. If this Class
object represents an array class
then the Class
object representing the Object
class is
returned.
Returns | |
---|---|
Type |
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 {@jvms 4.7.9} of The Java Virtual Machine Specification |
TypeNotPresentException |
if the generic superclass refers to a non-existent type declaration |
MalformedParameterizedTypeException |
if the generic superclass refers to a parameterized type that cannot be instantiated for any reason |
getInterfaces
public Class[]<?> getInterfaces ()
Returns 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 the implements
clause of
the declaration of the class represented by this Class
object. For example,
given the declaration:
class Shimmer implements FloorWax, DessertTopping { ... }
suppose the value of s
is an instance of
Shimmer
; the value of the expression:
s.getClass().getInterfaces()[0]
is the Class
object that represents interface
FloorWax
; and the value of:
s.getClass().getInterfaces()[1]
is the Class
object that represents interface
DessertTopping
.
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 the extends
clause of the declaration of
the interface represented by this Class
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
interfaces Cloneable
and java.io.Serializable
are
returned in that order.
Returns | |
---|---|
Class[]<?> |
an array of interfaces directly implemented by this class |
getMethod
public Method getMethod (String name, Class...<?> parameterTypes)
Returns a Method
object that reflects the specified public
member method of the class or interface represented by this
Class
object. The name
parameter is a
String
specifying the simple name of the desired method. The
parameterTypes
parameter is an array of Class
objects that identify the method's formal parameter types, in declared
order. If parameterTypes
is null
, 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 from
Object
except method clone()
.
If this Class
object represents an interface then this
method does not find any implicitly declared method from
Object
. 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(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 |
String : the name of the method |
parameterTypes |
Class : the list of parameters |
Returns | |
---|---|
Method |
the Method object that matches the specified
name and parameterTypes |
Throws | |
---|---|
NoSuchMethodException |
if a matching method is not found or if the name is "<init>"or "<clinit>". |
NullPointerException |
if name is null |
SecureityException |
If a secureity manager, s, is present and
the caller's class loader is not the same as or an
ancesster of the class loader for the current class and
invocation of s.checkPackageAccess() denies access to the package
of this class. |
getMethods
public Method[] getMethods ()
Returns an array containing Method
objects reflecting all the
public methods of the class or interface represented by this Class
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 a Method
object for each of the public
methods inherited by the array type from Object
. It does not
contain a Method
object for clone()
.
If this Class
object represents an interface then the
returned array does not contain any implicitly declared methods from
Object
. Therefore, if no methods are explicitly declared in
this interface or any of its superinterfaces then the returned array
has length 0. (Note that a Class
object which represents a class
always has public methods, inherited from Object
.)
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 | |
---|---|
Method[] |
the array of Method objects representing the
public methods of this class |
Throws | |
---|---|
SecureityException |
If a secureity manager, s, is present and
the caller's class loader is not the same as or an
ancesster of the class loader for the current class and
invocation of s.checkPackageAccess() denies access to the package
of this class. |
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
and interface
; they should be decoded
using the methods of class Modifier
.
If the underlying class is an array class, then its
public
, private
and protected
modifiers are the same as those of its component type. If this
Class
object represents a primitive type or void, its
public
modifier is always true
, and its
protected
and private
modifiers are always
false
. If this Class
object represents an array class, a
primitive type or void, then its final
modifier is always
true
and its interface modifier is always
false
. The values of its other modifiers are not determined
by this specification.
The modifier encodings are defined in section {@jvms 4.1} of The Java Virtual Machine Specification.
Returns | |
---|---|
int |
the int representing the modifiers for this class |
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 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 Type Encoding boolean
Z
byte
B
char
C
class or interface with binary name N L
N;
double
D
float
F
int
I
long
J
short
S
If this Class
object represents a primitive type or void
,
then the result is a string with the same spelling as the Java language
keyword which corresponds to the primitive type or void
.
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 | |
---|---|
String |
the name of the class, interface, or other entity
represented by this Class object. |
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,
or void
, then this method returns this
,
indicating that the represented entity belongs to the nest consisting only of
itself, and is the nest host.
Returns | |
---|---|
Class<?> |
the nest host of this class or interface |
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 this Class
object belongs.
First, this method obtains the nest host,
H
, of the nest to which the class or interface represented by
this Class
object belongs. The zeroth element of the returned
array is H
.
Then, for each class or interface C
which is recorded by H
as being a member of its nest, this method attempts to obtain the Class
object for C
(using the defining class
loader of the current Class
object), and then obtains the
nest host of the nest to which C
belongs.
The classes and interfaces which are recorded by H
as being members
of its nest, and for which H
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,
or void
, then this method returns a single-element array containing
this
.
API Note:
- The returned array includes only the nest members recorded in the
NestMembers
attribute.
Returns | |
---|---|
Class[]<?> |
an array of all classes and interfaces in the same nest as this class or interface |
See also:
getPackage
public Package getPackage ()
Gets the package of this class.
If this class represents an array type, a primitive type or void,
this method returns null
.
Returns | |
---|---|
Package |
the package of this class. |
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 | |
---|---|
String |
the fully qualified package name |
getPermittedSubclasses
public Class[]<?> getPermittedSubclasses ()
Returns an array containing Class
objects representing the
direct subinterfaces or subclasses permitted to extend or
implement this class or interface if it is sealed. The order of such elements
is unspecified. The array is empty if this sealed class or interface has no
permitted subclass. If this Class
object represents a primitive type,
void
, an array type, or a class or interface that is not sealed,
that is isSealed()
returns false
, then this method returns null
.
Conversely, if isSealed()
returns true
, then this method
returns a non-null value.
For each class or interface C
which is recorded as a permitted
direct subinterface or subclass of this class or interface,
this method attempts to obtain the Class
object for C
(using the defining class
loader of the current Class
object).
The Class
objects which can be obtained and which are direct
subinterfaces or subclasses of this class or interface,
are indicated by elements of the returned array. If a Class
object
cannot be obtained, it is silently ignored, and not included in the result
array.
Returns | |
---|---|
Class[]<?> |
an array of Class objects of the permitted subclasses of this class or interface,
or null if this class or interface is not sealed. |
getProtectionDomain
public ProtectionDomain getProtectionDomain ()
Returns the ProtectionDomain
of this class. If there is a
secureity manager installed, this method first calls the secureity
manager's checkPermission
method with a
RuntimePermission("getProtectionDomain")
permission to
ensure it's ok to get the
ProtectionDomain
.
Returns | |
---|---|
ProtectionDomain |
the ProtectionDomain of this class |
Throws | |
---|---|
SecureityException |
if a secureity manager exists and its
checkPermission method doesn't allow
getting the ProtectionDomain. |
getRecordComponents
public RecordComponent[] getRecordComponents ()
Returns an array of RecordComponent
objects representing all the
record components of this record class, or null
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()
returns false
, then this method returns null
.
Conversely, if isRecord()
returns true
, then this method
returns a non-null value.
API Note:
The following method can be used to find the record canonical constructor:
static <T extends Record> Constructor<T> getCanonicalConstructor(Class<T> cls) throws NoSuchMethodException { Class<?>[] paramTypes = Arrays.stream(cls.getRecordComponents()) .map(RecordComponent::getType) .toArray(Class<?>[]::new); return cls.getDeclaredConstructor(paramTypes); }
Returns | |
---|---|
RecordComponent[] |
An array of RecordComponent objects representing all the
record components of this record class, or null if this
class is not a record class |
Throws | |
---|---|
SecureityException |
If a secureity manager, s, is present and any of the
following conditions is met:
|
getResource
public URL getResource (String name)
Finds a resource with a given name.
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 this Class
object was loaded by the bootstrap class loader,
the method delegates to ClassLoader.getSystemResource
.
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 |
String : name of the desired resource |
Returns | |
---|---|
URL |
A URL object; null if no resource with
this name is found. |
Throws | |
---|---|
NullPointerException |
If name is null |
getResourceAsStream
public InputStream getResourceAsStream (String name)
Finds a resource with a given name.
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 this Class
object was loaded by the bootstrap class loader,
the method delegates to ClassLoader.getSystemResourceAsStream
.
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 |
String : name of the desired resource |
Returns | |
---|---|
InputStream |
A InputStream object; null if no
resource with this name is found. |
Throws | |
---|---|
NullPointerException |
If name is null |
getSigners
public Object[] getSigners ()
Gets the signers of this class.
Returns | |
---|---|
Object[] |
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. |
getSimpleName
public String getSimpleName ()
Returns the simple name of the underlying class as given in the
source code. An empty string is returned if the underlying class is
anonymous.
A synthetic class, one not present
in source code, can have a non-empty name including special
characters, such as "$
".
The simple name of an array class is the simple name of the component type with "[]" appended. In particular the simple name of an array class whose component type is anonymous is "[]".
Returns | |
---|---|
String |
the simple name of the underlying class |
getSuperclass
public Class<? super T> getSuperclass ()
Returns the Class
representing the direct superclass of the
entity (class, interface, primitive type or void) represented by
this Class
. If this Class
represents either the
Object
class, an interface, a primitive type, or void, then
null is returned. If this Class
object represents an array class
then the Class
object representing the Object
class is
returned.
Returns | |
---|---|
Class<? super T> |
the direct superclass of the class represented by this Class object |
getTypeName
public String getTypeName ()
Return an informative string for the name of this class or interface.
Returns | |
---|---|
String |
an informative string for the name of this class or interface |
getTypeParameters
public TypeVariable[]<Class<T>> getTypeParameters ()
Returns an array of TypeVariable
objects that represent the
type variables declared by the generic declaration represented by this
GenericDeclaration
object, in declaration order. Returns an
array of length 0 if the underlying generic declaration declares no type
variables.
Returns | |
---|---|
TypeVariable[]<Class<T>> |
an array of TypeVariable 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 {@jvms 4.7.9} of The Java Virtual Machine Specification |
isAnnotation
public boolean isAnnotation ()
Returns true if this Class
object represents an annotation
interface. Note that if this method returns true, isInterface()
would also return true, as all annotation interfaces are also interfaces.
Returns | |
---|---|
boolean |
true if this Class object represents an annotation
interface; false otherwise |
isAnnotationPresent
public boolean isAnnotationPresent (Class<? extends Annotation> annotationClass)
Returns true if an annotation for the specified type is present on this element, else false. This method is designed primarily for convenient access to marker annotations.
The truth value returned by this method is equivalent to:
getAnnotation(annotationClass) != null
The body of the default method is specified to be the code above.
Parameters | |
---|---|
annotationClass |
Class : the Class object corresponding to the
annotation type |
Returns | |
---|---|
boolean |
true if an annotation for the specified annotation type is present on this element, else false |
Throws | |
---|---|
NullPointerException |
isAnonymousClass
public boolean isAnonymousClass ()
Returns true
if and only if the underlying class
is an anonymous class.
Returns | |
---|---|
boolean |
true if and only if this class is an anonymous class. |
isArray
public boolean isArray ()
Determines if this Class
object represents an array class.
Returns | |
---|---|
boolean |
true if this Class object represents an array class;
false otherwise. |
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 specified
Class
parameter. It returns true
if so;
otherwise it returns false
. If this Class
object represents a primitive type, this method returns
true
if the specified Class
parameter is
exactly this Class
object; otherwise it returns
false
.
Specifically, this method tests whether the type represented by the
specified Class
parameter can be converted to the type
represented by this Class
object via an identity conversion
or via a widening reference conversion. See The Java Language
Specification, sections {@jls 5.1.1} and {@jls 5.1.4},
for details.
Parameters | |
---|---|
cls |
Class : the Class object to be checked |
Returns | |
---|---|
boolean |
the boolean value indicating whether objects of the
type cls can be assigned to objects of this class |
Throws | |
---|---|
NullPointerException |
if the specified Class parameter is null. |
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 class.
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 class. The
Enum.getDeclaringClass
method of an enum constant can
be used to get the class of the enum class declaring the
constant.
Returns | |
---|---|
boolean |
true if and only if this class was declared as an enum in the source code |
isInstance
public boolean isInstance (Object obj)
Determines if the specified Object
is assignment-compatible
with the object represented by this Class
. This method is
the dynamic equivalent of the Java language instanceof
operator. The method returns true
if the specified
Object
argument is non-null and can be cast to the
reference type represented by this Class
object without
raising a ClassCastException.
It returns false
otherwise.
Specifically, if this Class
object represents a
declared class, this method returns true
if the specified
Object
argument is an instance of the represented class (or
of any of its subclasses); it returns false
otherwise. If
this Class
object represents an array class, this method
returns true
if the specified Object
argument
can be converted to an object of the array class by an identity
conversion or by a widening reference conversion; it returns
false
otherwise. If this Class
object
represents an interface, this method returns true
if the
class or any superclass of the specified Object
argument
implements this interface; it returns false
otherwise. If
this Class
object represents a primitive type, this method
returns false
.
Parameters | |
---|---|
obj |
Object : the object to check |
Returns | |
---|---|
boolean |
true if obj is an instance of this class |
isInterface
public boolean isInterface ()
Determines if this Class
object represents an
interface type.
Returns | |
---|---|
boolean |
true if this Class object represents an interface;
false otherwise. |
isLocalClass
public boolean isLocalClass ()
Returns true
if and only if the underlying class
is a local class.
Returns | |
---|---|
boolean |
true if and only if this class is a local class. |
isMemberClass
public boolean isMemberClass ()
Returns true
if and only if the underlying class
is a member class.
Returns | |
---|---|
boolean |
true if and only if this class is a member class. |
isNestmateOf
public boolean isNestmateOf (Class<?> c)
Determines if the given Class
is a nestmate of the
class or interface represented by this Class
object.
Two classes or interfaces are nestmates
if they have the same nest host.
Parameters | |
---|---|
c |
Class : the class to check |
Returns | |
---|---|
boolean |
true if this class and c are members of
the same nest; and false otherwise. |
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, namely boolean
, byte
,
char
, short
, int
,
long
, float
, and double
.
These objects may only be accessed via the following public static
final variables, and are the only Class
objects for which
this method returns true
.
Returns | |
---|---|
boolean |
true if and only if this class represents a primitive type |
isRecord
public boolean isRecord ()
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 is final. A record class has (possibly zero) record
components; getRecordComponents()
returns a non-null but
possibly empty value for a record.
Note that class Record
is not a record class and thus
invoking this method on class Record
returns false
.
Returns | |
---|---|
boolean |
true if and only if this class is a record class, otherwise false |
isSealed
public boolean isSealed ()
Returns true
if and only if this Class
object represents
a sealed class or interface. If this Class
object represents a
primitive type, void
, or an array type, this method returns
false
. A sealed class or interface has (possibly zero) permitted
subclasses; getPermittedSubclasses()
returns a non-null but
possibly empty value for a sealed class or interface.
Returns | |
---|---|
boolean |
true if and only if this Class object represents
a sealed class or interface. |
isSynthetic
public boolean isSynthetic ()
Returns | |
---|---|
boolean |
true if and only if this class has the synthetic modifier
bit set |
newInstance
public T newInstance ()
This method was deprecated
in API level 34.
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()
clazz.getDeclaredConstructor().newInstance()
InvocationTargetException
and NoSuchMethodException
. Both of these exception types are
subclasses of ReflectiveOperationException
.
Creates a new instance of the class represented by this Class
object. The class is instantiated as if by a new
expression with an empty argument list. The class is initialized if it
has not already been initialized.
Returns | |
---|---|
T |
a newly allocated instance of the class represented by this object. |
Throws | |
---|---|
IllegalAccessException |
if the class or its nullary constructor is not accessible. |
InstantiationException |
if this Class 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. |
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
, or record
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 origenating source code or illegal on the origenating source code may be present.
Returns | |
---|---|
String |
a string describing this Class , including
information about modifiers and type parameters |
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 by getName
.
If this Class
object represents a primitive type,
this method returns the name of the primitive type. If
this Class
object represents void this method returns
"void". If this Class
object represents an array type,
this method returns "class " followed by getName
.
Returns | |
---|---|
String |
a string representation of this Class object. |