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.Serializable, AnnotatedElement, GenericDeclaration, Typepublic final class Class<T> extends Object implements Serializable, GenericDeclaration, Type, AnnotatedElement
Class represent classes and
interfaces in a running Java application. An enum is a kind of
class and an annotation 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 Class
objects are constructed automatically by the Java Virtual Machine as classes
are loaded and by calls to the defineClass method in the class
loader.
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. See Section 15.8.2 of
The Java™ Language Specification.
For example:
System.out.println("The name of class Foo is: "+Foo.class.getName());
ClassLoader.defineClass(byte[], int, int),
序列化表格| 限定符和类型 | 方法 | 说明 |
|---|---|---|
<U> Class<? extends U> |
asSubclass(Class<U> clazz) |
Casts this
Class object to represent a subclass of the class
represented by the specified class object. |
T |
cast(Object obj) |
Casts an object to the class or interface represented
by this
Class 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(String className) |
Returns the
Class object associated with the class or
interface with the given string name. |
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. |
<A extends Annotation> |
getAnnotation(Class<A> annotationClass) |
Returns this element's annotation for the specified type if
such an annotation is present, else null.
|
Annotation[] |
getAnnotations() |
Returns annotations that are present on this element.
|
<A extends Annotation> |
getAnnotationsByType(Class<A> annotationClass) |
Returns annotations that are associated with this element.
|
String |
getCanonicalName() |
Returns the canonical name of the underlying class as
defined by the Java Language Specification.
|
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. |
ClassLoader |
getClassLoader() |
Returns the class loader for the class.
|
Class<?> |
getComponentType() |
Returns the
Class representing the component type of an
array. |
Constructor<T> |
getConstructor(Class<?>... parameterTypes) |
Returns a
Constructor object that reflects the specified
public constructor of the class represented by this Class
object. |
Constructor<?>[] |
getConstructors() |
Returns an array containing
Constructor objects reflecting
all the public constructors of the class represented by this
Class object. |
<A extends Annotation> |
getDeclaredAnnotation(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.
|
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. |
Constructor<T> |
getDeclaredConstructor(Class<?>... parameterTypes) |
Returns a
Constructor object that reflects the specified
constructor of the class or interface represented by this
Class object. |
Constructor<?>[] |
getDeclaredConstructors() |
Returns an array of
Constructor objects reflecting all the
constructors declared by the class represented by this
Class object. |
Field |
getDeclaredField(String name) |
Returns a
Field object that reflects the specified declared
field of the class or interface represented by this Class
object. |
Field[] |
getDeclaredFields() |
Returns an array of
Field objects reflecting all the fields
declared by the class or interface represented by this
Class object. |
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. |
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. |
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. |
Class<?> |
getEnclosingClass() |
Returns the immediately enclosing class of the underlying
class.
|
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. |
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. |
T[] |
getEnumConstants() |
Returns the elements of this enum class or null if this
Class object does not represent an enum type.
|
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. |
Field[] |
getFields() |
Returns an array containing
Field objects reflecting all
the accessible public fields of the class or interface represented by
this Class object. |
Type[] |
getGenericInterfaces() |
Returns the
Types representing the interfaces
directly implemented by the class or interface represented by
this object. |
Type |
getGenericSuperclass() |
Returns the
Type representing the direct superclass of
the entity (class, interface, primitive type or void) represented by
this Class. |
Class<?>[] |
getInterfaces() |
Determines the interfaces implemented by the class or interface
represented by this object.
|
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. |
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. |
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 object,
as a String. |
Package |
getPackage() |
Gets the package for this class.
|
ProtectionDomain |
getProtectionDomain() |
Returns the
ProtectionDomain of this 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.
|
String |
getSimpleName() |
Returns the simple name of the underlying class as given in the
source code.
|
Class<? super T> |
getSuperclass() |
Returns the
Class representing the superclass of the entity
(class, interface, primitive type or void) represented by this
Class. |
String |
getTypeName() |
Return an informative string for the name of this type.
|
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. |
boolean |
isAnnotation() |
Returns true if this
Class 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() |
Returns
true if and only if the underlying class
is an anonymous class. |
boolean |
isArray() |
Determines if this
Class object represents an array class. |
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. |
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
Object is assignment-compatible
with the object represented by this Class. |
boolean |
isInterface() |
Determines if the specified
Class object represents an
interface type. |
boolean |
isLocalClass() |
Returns
true if and only if the underlying class
is a local class. |
boolean |
isMemberClass() |
Returns
true if and only if the underlying class
is a member class. |
boolean |
isPrimitive() |
Determines if the specified
Class object represents a
primitive type. |
boolean |
isSynthetic() |
Returns
true if this class is a synthetic class;
returns false otherwise. |
T |
newInstance() |
Creates a new instance of the class represented by this
Class
object. |
String |
toGenericString() |
Returns a string describing this
Class, including
information about modifiers and type parameters. |
String |
toString() |
Converts the object to a string.
|
getDeclaredAnnotationsByTypepublic String toString()
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".public String toGenericString()
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, or
@interface, as appropriate), followed
by the type's name, followed by an angle-bracketed
comma-separated list of the type's 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.
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.
Class, including
information about modifiers and type parameterspublic static Class<?> forName(String className) throws ClassNotFoundException
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.
className - the fully qualified name of the desired class.Class object for the class with the
specified name.LinkageError - if the linkage failsExceptionInInitializerError - if the initialization provoked
by this method failsClassNotFoundException - if the class cannot be locatedpublic static Class<?> forName(String name, boolean initialize, ClassLoader loader) throws ClassNotFoundException
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, load, and link 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 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.
If the loader is null, and a security
manager is present, and the caller's class loader is not null, then this
method calls the security manager's checkPermission method
with a RuntimePermission("getClassLoader") permission to
ensure it's ok to access the bootstrap class loader.
name - fully qualified name of the desired classinitialize - if true the class will be initialized.
See Section 12.4 of The Java Language Specification.loader - class loader from which the class must be loadedLinkageError - if the linkage failsExceptionInInitializerError - if the initialization provoked
by this method failsClassNotFoundException - if the class cannot be located by
the specified class loaderforName(String),
ClassLoaderpublic T newInstance() throws IllegalAccessException, InstantiationException
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.
Note that 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.
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.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 of SecurityManager#checkPackageAccess denies access to the package
of this class.public boolean isInstance(Object obj)
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.
obj - the object to checkobj is an instance of this classpublic boolean isAssignableFrom(Class<?> cls)
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 5.1.1 and 5.1.4 , for details.
cls - the Class object to be checkedboolean value indicating whether objects of the
type cls can be assigned to objects of this classNullPointerException - if the specified Class parameter is
null.public boolean isInterface()
Class object represents an
interface type.true if this object represents an interface;
false otherwise.public boolean isArray()
Class object represents an array class.true if this object represents an array class;
false otherwise.public boolean isPrimitive()
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.
Boolean.TYPE,
Character.TYPE,
Byte.TYPE,
Short.TYPE,
Integer.TYPE,
Long.TYPE,
Float.TYPE,
Double.TYPE,
Void.TYPEpublic boolean isAnnotation()
Class object represents an annotation
type. Note that if this method returns true, isInterface()
would also return true, as all annotation types are also interfaces.true if this class object represents an annotation
type; false otherwisepublic boolean isSynthetic()
true if this class is a synthetic class;
returns false otherwise.true if and only if this class is a synthetic class as
defined by the Java Language Specification.public String getName()
Class object,
as a String.
If this class object represents a reference type that is not an array type then the binary name of the class is returned, as specified by The Java™ Language Specification.
If this class object represents a primitive type or void, then the
name returned is a String equal to the Java language
keyword corresponding to the primitive type or void.
If this class object represents a class of arrays, then the internal
form of the name consists of the name of the element type preceded by
one or more '[' characters representing the depth of the array
nesting. The encoding of element type names is as follows:
Element Type Encoding boolean Z byte B char C class or interface Lclassname; double D float F int I long J short S
The class or interface name classname is the binary name of the class specified above.
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"
public ClassLoader getClassLoader()
If a security manager is present, and the caller's class loader is
not null and the caller's class loader is not the same as or an ancestor of
the class loader for the class whose class loader is requested, then
this method calls the security manager's checkPermission
method with a RuntimePermission("getClassLoader")
permission to ensure it's ok to access the class loader for the class.
If this object represents a primitive type or void, null is returned.
SecurityException - if a security manager exists and its
checkPermission method denies
access to the class loader for the class.ClassLoader,
SecurityManager.checkPermission(java.security.Permission),
RuntimePermissionpublic TypeVariable<Class<T>>[] getTypeParameters()
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.getTypeParameters 在接口中 GenericDeclarationTypeVariable objects that represent
the type variables declared by this generic declarationGenericSignatureFormatError - if the generic
signature of this generic declaration does not conform to
the format specified in
The Java™ Virtual Machine Specificationpublic Class<? super T> getSuperclass()
Class representing the 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 object represents an array class then the
Class object representing the Object class is
returned.public Type getGenericSuperclass()
Type representing the direct superclass of
the entity (class, interface, primitive type or void) represented by
this Class.
If the superclass is a parameterized type, the Type
object returned must accurately reflect the actual type
parameters 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 represents either the Object
class, an interface, a primitive type, or void, then null is
returned. If this object represents an array class then the
Class object representing the Object class is
returned.
GenericSignatureFormatError - if the generic
class signature does not conform to the format specified in
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 reasonpublic Package getPackage()
Packages have attributes for versions and specifications only if the information was defined in the manifests that accompany the classes, and if the class loader created the package instance with the attributes from the manifest.
public Class<?>[] getInterfaces()
If this object represents a class, the return value is an array
containing objects representing all interfaces 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 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 object represents an interface, the array contains objects
representing all interfaces 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 object.
If this object represents a class or interface that implements no interfaces, the method returns an array of length 0.
If this 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.
public Type[] getGenericInterfaces()
Types representing the interfaces
directly implemented by the class or interface represented by
this object.
If a superinterface is a parameterized type, the
Type object returned for it must accurately reflect
the actual type parameters 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 object represents a class, the return value is an
array containing objects representing all interfaces
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 object. In the case of an array class, the
interfaces Cloneable and Serializable are
returned in that order.
If this 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 object.
If this object represents a class or interface that implements no interfaces, the method returns an array of length 0.
If this object represents a primitive type or void, the method returns an array of length 0.
GenericSignatureFormatError - if the generic class signature does not conform to the format
specified in
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 reasonpublic Class<?> getComponentType()
Class representing the component type of an
array. If this class does not represent an array class this method
returns null.Class representing the component type of this
class if this class is an arrayArraypublic int getModifiers()
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 represents a primitive type or void, its
public modifier is always true, and its
protected and private modifiers are always
false. If this 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 The Java Virtual Machine Specification, table 4.1.
int representing the modifiers for this classModifierpublic Object[] getSigners()
public Method getEnclosingMethod() throws SecurityException
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 type
declaration, instance initializer or static initializer.null.SecurityException - If a security manager, s, is present and any of the
following conditions is met:
SecurityManager#checkPermission method with
RuntimePermission("accessDeclaredMembers")
denies access to the methods within the enclosing class
SecurityManager#checkPackageAccess denies access to the package
of the enclosing class
public Constructor<?> getEnclosingConstructor() throws SecurityException
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 type declaration,
instance initializer or static initializer.null.SecurityException - If a security manager, s, is present and any of the
following conditions is met:
SecurityManager#checkPermission method with
RuntimePermission("accessDeclaredMembers")
denies access to the constructors within the enclosing class
SecurityManager#checkPackageAccess denies access to the package
of the enclosing class
public Class<?> getDeclaringClass() throws SecurityException
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.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 of SecurityManager#checkPackageAccess
denies access to the package of the declaring classpublic Class<?> getEnclosingClass() throws SecurityException
null.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 of SecurityManager#checkPackageAccess
denies access to the package of the enclosing classpublic String getSimpleName()
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 "[]".
public String getTypeName()
getTypeName 在接口中 Typepublic String getCanonicalName()
null otherwise.public boolean isAnonymousClass()
true if and only if the underlying class
is an anonymous class.true if and only if this class is an anonymous class.public boolean isLocalClass()
true if and only if the underlying class
is a local class.true if and only if this class is a local class.public boolean isMemberClass()
true if and only if the underlying class
is a member class.true if and only if this class is a member class.public Class<?>[] getClasses()
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.Class objects representing the public
members of this classSecurityException - 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 of SecurityManager#checkPackageAccess denies access to the package
of this class.public Field[] getFields() throws SecurityException
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
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.
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.
Field objects representing the
public fieldsSecurityException - 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 of SecurityManager#checkPackageAccess denies access to the package
of this class.public Method[] getMethods() throws SecurityException
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 a type that has multiple
public 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 type with a class
initialization method <clinit>, then the returned array does
not have a corresponding Method object.
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.)
If this Class object represents a primitive type or void,
then the returned array has length 0.
Static methods declared in superinterfaces of the class or interface
represented by this Class object are not considered members of
the class or interface.
The elements in the returned array are not sorted and are not in any particular order.
Method objects representing the
public methods of this classSecurityException - 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 of SecurityManager#checkPackageAccess denies access to the package
of this class.public Constructor<?>[] getConstructors() throws SecurityException
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.
Note that 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 is
Constructor<?>[] and not Constructor<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 hold Constructor objects for
different classes, which would violate the type guarantees of
Constructor<T>[].Constructor objects representing the
public constructors of this classSecurityException - 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 of SecurityManager#checkPackageAccess denies access to the package
of this class.public Field getField(String name) throws NoSuchFieldException, SecurityException
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 object:
NoSuchFieldException
is thrown. If this Class object represents an array type, then this
method does not find the length field of the array type.
name - the field nameField object of this class specified by
nameNoSuchFieldException - if a field with the specified name is
not found.NullPointerException - if name is nullSecurityException - 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 of SecurityManager#checkPackageAccess denies access to the package
of this class.public Method getMethod(String name, Class<?>... parameterTypes) throws NoSuchMethodException, SecurityException
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 the name is "<init>" or "<clinit>" a
NoSuchMethodException is raised. Otherwise, the method to
be reflected is determined by the algorithm that follows. Let C be the
class or interface represented by this object:
Object, then this algorithm is
invoked recursively on the superclass of C.Object, or if C is an interface, then
the superinterfaces of C (if any) are searched for a matching
method. If any such method is found, it is reflected.To find a matching method in a class or interface C: If C declares exactly one public method with the specified name and exactly the same formal parameter types, that is the method reflected. If more than one such method is found in C, and one of these methods has a return type that is more specific than any of the others, that method is reflected; otherwise one of the methods is chosen arbitrarily.
Note that there may be more than one matching method 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 method being overridden would have the same signature but different return types.
If this Class object represents an array type, then this
method does not find the clone() method.
Static methods declared in superinterfaces of the class or interface
represented by this Class object are not considered members of
the class or interface.
name - the name of the methodparameterTypes - the list of parametersMethod object that matches the specified
name and parameterTypesNoSuchMethodException - if a matching method is not found
or if the name is "<init>"or "<clinit>".NullPointerException - if name is nullSecurityException - 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 of SecurityManager#checkPackageAccess denies access to the package
of this class.public Constructor<T> getConstructor(Class<?>... parameterTypes) throws NoSuchMethodException, SecurityException
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.
parameterTypes - the parameter arrayConstructor object of the public constructor that
matches the specified parameterTypesNoSuchMethodException - 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 of SecurityManager#checkPackageAccess denies access to the package
of this class.public Class<?>[] getDeclaredClasses() throws SecurityException
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.Class objects representing all the
declared members of this classSecurityException - If a security manager, s, is present and any of the
following conditions is met:
SecurityManager#checkPermission method with
RuntimePermission("accessDeclaredMembers")
denies access to the declared classes within this class
SecurityManager#checkPackageAccess denies access to the package
of this class
public Field[] getDeclaredFields() throws SecurityException
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.
Field objects representing all the
declared fields of this classSecurityException - If a security manager, s, is present and any of the
following conditions is met:
SecurityManager#checkPermission method with
RuntimePermission("accessDeclaredMembers")
denies access to the declared fields within this class
SecurityManager#checkPackageAccess denies access to the package
of this class
public Method[] getDeclaredMethods() throws SecurityException
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.
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 a Method 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 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.
Method objects representing all the
declared methods of this classSecurityException - If a security manager, s, is present and any of the
following conditions is met:
SecurityManager#checkPermission method with
RuntimePermission("accessDeclaredMembers")
denies access to the declared methods within this class
SecurityManager#checkPackageAccess denies access to the package
of this class
public Constructor<?>[] getDeclaredConstructors() throws SecurityException
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 8.2.
Constructor objects representing all the
declared constructors of this classSecurityException - If a security manager, s, is present and any of the
following conditions is met:
SecurityManager#checkPermission method with
RuntimePermission("accessDeclaredMembers")
denies access to the declared constructors within this class
SecurityManager#checkPackageAccess denies access to the package
of this class
public Field getDeclaredField(String name) throws NoSuchFieldException, SecurityException
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.
name - the name of the fieldField object for the specified field in this
classNoSuchFieldException - if a field with the specified name is
not found.NullPointerException - if name is nullSecurityException - If a security manager, s, is present and any of the
following conditions is met:
SecurityManager#checkPermission method with
RuntimePermission("accessDeclaredMembers")
denies access to the declared field
SecurityManager#checkPackageAccess denies access to the package
of this class
public Method getDeclaredMethod(String name, Class<?>... parameterTypes) throws NoSuchMethodException, SecurityException
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.
name - the name of the methodparameterTypes - the parameter arrayMethod object for the method of this class
matching the specified name and parametersNoSuchMethodException - if a matching method is not found.NullPointerException - if name is nullSecurityException - If a security manager, s, is present and any of the
following conditions is met:
SecurityManager#checkPermission method with
RuntimePermission("accessDeclaredMembers")
denies access to the declared method
SecurityManager#checkPackageAccess denies access to the package
of this class
public Constructor<T> getDeclaredConstructor(Class<?>... parameterTypes) throws NoSuchMethodException, SecurityException
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.parameterTypes - the parameter arrayConstructor object for the constructor with the
specified parameter listNoSuchMethodException - if a matching method is not found.SecurityException - If a security manager, s, is present and any of the
following conditions is met:
SecurityManager#checkPermission method with
RuntimePermission("accessDeclaredMembers")
denies access to the declared constructor
SecurityManager#checkPackageAccess denies access to the package
of this class
public InputStream getResourceAsStream(String name)
ClassLoader#getSystemResourceAsStream.
Before delegation, an absolute resource name is constructed from the given resource name using this algorithm:
name begins with a '/'
('\u002f'), then the absolute name of the resource is the
portion of the name following the '/'.
modified_package_name/name
Where the modified_package_name is the package name of this
object with '/' substituted for '.'
('\u002e').
name - name of the desired resourceInputStream object or null if
no resource with this name is foundNullPointerException - If name is nullpublic URL getResource(String name)
ClassLoader#getSystemResource.
Before delegation, an absolute resource name is constructed from the given resource name using this algorithm:
name begins with a '/'
('\u002f'), then the absolute name of the resource is the
portion of the name following the '/'.
modified_package_name/name
Where the modified_package_name is the package name of this
object with '/' substituted for '.'
('\u002e').
name - name of the desired resourceURL object or null if no
resource with this name is foundpublic ProtectionDomain getProtectionDomain()
ProtectionDomain of this class. If there is a
security manager installed, this method first calls the security
manager's checkPermission method with a
RuntimePermission("getProtectionDomain") permission to
ensure it's ok to get the
ProtectionDomain.SecurityException - if a security manager exists and its
checkPermission method doesn't allow
getting the ProtectionDomain.ProtectionDomain,
SecurityManager.checkPermission(java.security.Permission),
RuntimePermissionpublic boolean desiredAssertionStatus()
Few programmers will have any need for this method; it is provided for the benefit of the JRE 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.
ClassLoader.setClassAssertionStatus(java.lang.String, boolean),
ClassLoader.setPackageAssertionStatus(java.lang.String, boolean),
ClassLoader.setDefaultAssertionStatus(boolean)public boolean isEnum()
public T[] getEnumConstants()
public T cast(Object obj)
Class object.obj - the object to be castClassCastException - if the object is not
null and is not assignable to the type T.public <U> Class<? extends U> asSubclass(Class<U> clazz)
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).
U - the type to cast this class object toclazz - the class of the type to cast this class object toClass object, cast to represent a subclass of
the specified class object.ClassCastException - if this Class object does not
represent a subclass of the specified class (here "subclass" includes
the class itself).public <A extends Annotation> A getAnnotation(Class<A> annotationClass)
AnnotatedElementgetAnnotation 在接口中 AnnotatedElementA - the type of the annotation to query for and return if presentannotationClass - the Class object corresponding to the
annotation typeNullPointerException - if the given annotation class is nullpublic boolean isAnnotationPresent(Class<? extends Annotation> annotationClass)
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.
isAnnotationPresent 在接口中 AnnotatedElementannotationClass - the Class object corresponding to the
annotation typeNullPointerException - if the given annotation class is nullpublic <A extends Annotation> A[] getAnnotationsByType(Class<A> annotationClass)
AnnotatedElementAnnotatedElement.getAnnotation(java.lang.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.getAnnotationsByType 在接口中 AnnotatedElementA - the type of the annotation to query for and return if presentannotationClass - the Class object corresponding to the
annotation typeNullPointerException - if the given annotation class is nullpublic Annotation[] getAnnotations()
AnnotatedElementgetAnnotations 在接口中 AnnotatedElementpublic <A extends Annotation> A getDeclaredAnnotation(Class<A> annotationClass)
AnnotatedElementgetDeclaredAnnotation 在接口中 AnnotatedElementA - the type of the annotation to query for and return if directly presentannotationClass - the Class object corresponding to the
annotation typeNullPointerException - if the given annotation class is nullpublic Annotation[] getDeclaredAnnotations()
AnnotatedElementgetDeclaredAnnotations 在接口中 AnnotatedElement