java.lang.Class<T>
is new.
java.lang.Object
public final class Class<T>
Instances of the class 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 (JLS Section 15.8.2 ). For example:
System.out.println("The name of class Foo is: "+Foo.class.getName());
| Method Summary | ||
|---|---|---|
|
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. |
|
|
getAnnotation
(
Class
<A> annotationClass) Returns this element's annotation for the specified type if such an annotation is present, else null. |
|
| Annotation [] |
getAnnotations
() Returns all annotations present on this element. |
|
|
String
|
getCanonicalName
()
Returns the canonical name of the 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. |
|
| Annotation [] |
getDeclaredAnnotations
() Returns all 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 of Method objects reflecting all the methods declared by the class or interface represented by this Class object. |
|
| 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 Type s 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 member 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. |
|
| 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 |
toString
() Converts the object to a string. |
|
| Methods inherited from class java.lang. Object |
|---|
| clone , equals , finalize , getClass , hashCode , notify , notifyAll , wait , wait , wait |
| Method Detail |
|---|
public String toString()
public static Class<?> forName(String className)
throws ClassNotFoundException
where currentLoader denotes the defining class loader of the current class.Class.forName(className, true, currentLoader)
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.
public static Class<?> forName(String name,
boolean initialize,
ClassLoader loader)
throws ClassNotFoundException
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.
public T newInstance()
throws InstantiationException,
IllegalAccessException
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
.
public boolean isInstance(Object obj)
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.
public boolean isAssignableFrom(Class<?> cls)
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.
public boolean isInterface()
public boolean isArray()
public boolean isPrimitive()
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.
public boolean isAnnotation()
public boolean isSynthetic()
public String getName()
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, Second Edition.
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 L classname; 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.
public TypeVariable<Class<T>>[] getTypeParameters()
public Class<? super T> getSuperclass()
public Type getGenericSuperclass()
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.
public 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: is the Class object that represents interface FloorWax; and the value of:s.getClass().getInterfaces()[0]
is the Class object that represents interface DessertTopping.s.getClass().getInterfaces()[1]
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.
public Type[] getGenericInterfaces()
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.
public Class<?> getComponentType()
public int getModifiers()
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.
public Object[] getSigners()
public Method getEnclosingMethod()
public Constructor<?> getEnclosingConstructor()
public Class<?> getDeclaringClass()
getEnclosingClass
Returns the immediately enclosing class of the underlying class. If the underlying class is a top level class this method returns
null
.
Returns:
the immediately enclosing class of the underlying class
Since:
1.5
getSimpleName
Returns the simple name of the underlying class as given in the source code. Returns an empty string if the underlying class is anonymous.
The simple name of an array is the simple name of the component type with "[]" appended. In particular the simple name of an array whose component type is anonymous is "[]".
Returns:
the simple name of the underlying class
Since:
1.5
getCanonicalName
Returns the canonical name of the the underlying class as defined by the Java Language Specification. Returns null if the underlying class does not have a canonical name (i.e., if it is a local or anonymous class or an array whose component type does not have a canonical name).
Returns:
the canonical name of the underlying class if it exists, and
null
otherwise.
Since:
1.5
isAnonymousClass
Returns
true
if and only if the underlying class is an anonymous class.
Returns:
true
if and only if this class is an anonymous class.
Since:
1.5
isLocalClass
Returns
true
if and only if the underlying class is a local class.
Returns:
true
if and only if this class is a local class.
Since:
1.5
isMemberClass
Returns
true
if and only if the underlying class is a member class.
Returns:
true
if and only if this class is a member class.
Since:
1.5
public Class[] getClasses()
public Field[] getFields()
throws SecurityException
Specifically, if this Class object represents a class, this method returns the public fields of this class and of all its superclasses. If this Class object represents an interface, this method returns the fields of this interface and of all its superinterfaces.
The implicit length field for array class is not reflected by this method. User code should use the methods of class Array to manipulate arrays.
See The Java Language Specification, sections 8.2 and 8.3.
public Method[] getMethods()
throws SecurityException
(public)
member methods inherited from the Object class. The elements in the array returned are not sorted and are not in any particular order. This method returns an array of length 0 if this Class object represents a class or interface that has no public member methods, or if this Class object represents a primitive type or void. The class initialization method <clinit> is not included in the returned array. If the class declares multiple public member methods with the same parameter types, they are all included in the returned array.
See The Java Language Specification, sections 8.2 and 8.4.
public Constructor[] getConstructors()
throws SecurityException
public Field getField(String name)
throws NoSuchFieldException,
SecurityException
The field to be reflected is determined by the algorithm that follows. Let C be the class represented by this object:
See The Java Language Specification, sections 8.2 and 8.3.
public Method getMethod(String name,
Class... parameterTypes)
throws NoSuchMethodException,
SecurityException
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 represented by this object:
See The Java Language Specification, sections 8.2 and 8.4.
public Constructor<T> getConstructor(Class... parameterTypes)
throws NoSuchMethodException,
SecurityException
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.
public Class[] getDeclaredClasses()
throws SecurityException
public Field[] getDeclaredFields()
throws SecurityException
See The Java Language Specification, sections 8.2 and 8.3.
public Method[] getDeclaredMethods()
throws SecurityException
See The Java Language Specification, section 8.2.
public Constructor[] getDeclaredConstructors()
throws SecurityException
See The Java Language Specification, section 8.2.
public Field getDeclaredField(String name)
throws NoSuchFieldException,
SecurityException
public Method getDeclaredMethod(String name,
Class... parameterTypes)
throws NoSuchMethodException,
SecurityException
public Constructor<T> getDeclaredConstructor(Class... parameterTypes)
throws NoSuchMethodException,
SecurityException
public InputStream getResourceAsStream(String name)
Before delegation, an absolute resource name is constructed from the given resource name using this algorithm:
modified_package_name/name
Where the modified_package_name is the package name of this object with '/' substituted for '.' ( '\u002e' ).
public URL getResource(String name)
Before delegation, an absolute resource name is constructed from the given resource name using this algorithm:
modified_package_name/name
Where the modified_package_name is the package name of this object with '/' substituted for '.' ( '\u002e' ).
public ProtectionDomain getProtectionDomain()
public 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.
public boolean isEnum()
Since:
1.5
public T[] getEnumConstants()
Since:
1.5
public T cast(Object obj)
public <U> Class<? extends U> asSubclass(Class<U> clazz)
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).
Returns:
this
Class
object, cast to represent a subclass of the specified class object.
Since:
1.5
public <A extends Annotation> A getAnnotation(Class<A> annotationClass)
public boolean isAnnotationPresent(Class<? extends Annotation> annotationClass)
public Annotation[] getAnnotations()
public Annotation[] getDeclaredAnnotations()