public final class

Class

extends Object
implements Serializable AnnotatedElement GenericDeclaration Type
java.lang.Object
   ↳ java.lang.Class<T>

Class Overview

The in-memory representation of a Java class. This representation serves as the starting point for querying class-related information, a process usually called "reflection". There are basically three types of Class instances: those representing real classes and interfaces, those representing primitive types, and those representing array classes.

Class instances representing object types (classes or interfaces)

These represent an ordinary class or interface as found in the class hierarchy. The name associated with these Class instances is simply the fully qualified class name of the class or interface that it represents. In addition to this human-readable name, each class is also associated by a so-called signature, which is the letter "L", followed by the class name and a semicolon (";"). The signature is what the runtime system uses internally for identifying the class (for example in a DEX file).

Classes representing primitive types

These represent the standard Java primitive types and hence share their names (for example "int" for the int primitive type). Although it is not possible to create new instances based on these Class instances, they are still useful for providing reflection information, and as the component type of array classes. There is one Class instance for each primitive type, and their signatures are:

  • B representing the byte primitive type
  • S representing the short primitive type
  • I representing the int primitive type
  • J representing the long primitive type
  • F representing the float primitive type
  • D representing the double primitive type
  • C representing the char primitive type
  • Z representing the boolean primitive type
  • V representing void function return values

Classes representing array classes

These represent the classes of Java arrays. There is one such Class instance per combination of array leaf component type and arity (number of dimensions). In this case, the name associated with the Class consists of one or more left square brackets (one per dimension in the array) followed by the signature of the class representing the leaf component type, which can be either an object type or a primitive type. The signature of a Class representing an array type is the same as its name. Examples of array class signatures are:

  • [I representing the int[] type
  • [Ljava/lang/String; representing the String[] type
  • [[[C representing the char[][][] type (three dimensions!)

Summary

Public Methods
<U> Class<? extends U> asSubclass(Class<U> clazz)
Casts this Class to represent a subclass of the specified class.
T cast(Object obj)
Casts the specified object to the type represented by this Class.
boolean desiredAssertionStatus()
Returns the assertion status for the class represented by this Class.
static Class<?> forName(String className, boolean initializeBoolean, ClassLoader classLoader)
Returns a Class object which represents the class with the specified name.
static Class<?> forName(String className)
Returns a Class object which represents the class with the specified name.
<A extends Annotation> A getAnnotation(Class<A> annotationType)
Annotation[] getAnnotations()
Returns all the annotations of this class.
String getCanonicalName()
Returns the canonical name of this class.
ClassLoader getClassLoader()
Returns the class loader which was used to load the class represented by this Class.
Class[]<?> getClasses()
Returns an array containing Class objects for all public classes and interfaces that are members of this class.
Class<?> getComponentType()
Returns a Class object which represents the component type if this class represents an array type.
Constructor<T> getConstructor(Class...<?> parameterTypes)
Returns a Constructor object which represents the public constructor matching the specified parameter types.
Constructor[]<?> getConstructors()
Returns an array containing Constructor objects for all public constructors for the class represented by this Class.
Annotation[] getDeclaredAnnotations()
Returns the annotations that are directly defined on the class represented by this Class.
Class[]<?> getDeclaredClasses()
Returns an array containing Class objects for all classes and interfaces that are declared as members of the class which this Class represents.
Constructor<T> getDeclaredConstructor(Class...<?> parameterTypes)
Returns a Constructor object which represents the constructor matching the specified parameter types that is declared by the class represented by this Class.
Constructor[]<?> getDeclaredConstructors()
Returns an array containing Constructor objects for all constructors declared in the class represented by this Class.
Field getDeclaredField(String name)
Returns a Field object for the field with the specified name which is declared in the class represented by this Class.
Field[] getDeclaredFields()
Returns an array containing Field objects for all fields declared in the class represented by this Class.
Method getDeclaredMethod(String name, Class...<?> parameterTypes)
Returns a Method object which represents the method matching the specified name and parameter types that is declared by the class represented by this Class.
Method[] getDeclaredMethods()
Returns an array containing Method objects for all methods declared in the class represented by this Class.
Class<?> getDeclaringClass()
Returns the declaring Class of this Class.
Class<?> getEnclosingClass()
Returns the enclosing Class of this Class.
Constructor<?> getEnclosingConstructor()
Gets the enclosing Constructor of this Class, if it is an anonymous or local/automatic class; otherwise null.
Method getEnclosingMethod()
Gets the enclosing Method of this Class, if it is an anonymous or local/automatic class; otherwise null.
T[] getEnumConstants()
Gets the enum constants associated with this Class.
Field getField(String name)
Returns a Field object which represents the public field with the specified name.
Field[] getFields()
Returns an array containing Field objects for all public fields for the class C represented by this Class.
Type[] getGenericInterfaces()
Gets the Types of the interfaces that this Class directly implements.
Type getGenericSuperclass()
Gets the Type that represents the superclass of this class.
Class[]<?> getInterfaces()
Returns an array of Class objects that match the interfaces specified in the implements declaration of the class represented by this Class.
Method getMethod(String name, Class...<?> parameterTypes)
Returns a Method object which represents the public method with the specified name and parameter types.
Method[] getMethods()
Returns an array containing Method objects for all public methods for the class C represented by this Class.
int getModifiers()
Returns an integer that represents the modifiers of the class represented by this Class.
String getName()
Returns the name of the class represented by this Class.
Package getPackage()
Returns the Package of which the class represented by this Class is a member.
ProtectionDomain getProtectionDomain()
Returns null.
URL getResource(String resName)
Returns the URL of the resource specified by resName.
InputStream getResourceAsStream(String resName)
Returns a read-only stream for the contents of the resource specified by resName.
Object[] getSigners()
Returns null.
String getSimpleName()
Returns the simple name of the class represented by this Class as defined in the source code.
Class<? super T> getSuperclass()
Returns the Class object which represents the superclass of the class represented by this Class.
synchronized TypeVariable[]<Class<T>> getTypeParameters()
Returns an array containing TypeVariable objects for type variables declared by the generic class represented by this Class.
boolean isAnnotation()
Indicates whether this Class represents an annotation class.
boolean isAnnotationPresent(Class<? extends Annotation> annotationType)
Indicates whether or not this element has an annotation with the specified annotation type (including inherited annotations).
boolean isAnonymousClass()
Indicates whether the class represented by this Class is anonymously declared.
boolean isArray()
Indicates whether the class represented by this Class is an array class.
boolean isAssignableFrom(Class<?> cls)
Indicates whether the specified class type can be converted to the class represented by this Class.
boolean isEnum()
Indicates whether the class represented by this Class is an enum.
boolean isInstance(Object object)
Indicates whether the specified object can be cast to the class represented by this Class.
boolean isInterface()
Indicates whether this Class represents an interface.
boolean isLocalClass()
Indicates whether the class represented by this Class is defined locally.
boolean isMemberClass()
Indicates whether the class represented by this Class is a member class.
boolean isPrimitive()
Indicates whether this Class represents a primitive type.
boolean isSynthetic()
Indicates whether this Class represents a synthetic type.
T newInstance()
Returns a new instance of the class represented by this Class, created by invoking the default (that is, zero-argument) constructor.
String toString()
Returns a string containing a concise, human-readable description of this object.
[Expand]
Inherited Methods
From class java.lang.Object
From interface java.lang.reflect.AnnotatedElement
From interface java.lang.reflect.GenericDeclaration

Public Methods

public Class<? extends U> asSubclass (Class<U> clazz)

Since: API Level 1

Casts this Class to represent a subclass of the specified class. If successful, this Class is returned; otherwise a ClassCastException is thrown.

Parameters
clazz the required type.
Returns
  • this Class cast as a subclass of the given type.
Throws
ClassCastException if this Class cannot be cast to the specified type.

public T cast (Object obj)

Since: API Level 1

Casts the specified object to the type represented by this Class. If the object is null then the result is also null.

Parameters
obj the object to cast.
Returns
  • the object that has been cast.
Throws
ClassCastException if the object cannot be cast to the specified type.

public boolean desiredAssertionStatus ()

Since: API Level 1

Returns the assertion status for the class represented by this Class. Assertion is enabled / disabled based on the class loader, package or class default at runtime.

Returns
  • the assertion status for the class represented by this Class.

public static Class<?> forName (String className, boolean initializeBoolean, ClassLoader classLoader)

Since: API Level 1

Returns a Class object which represents the class with the specified name. The name should be the name of a class as described in the class definition, however Classes representing primitive types can not be found using this method. Security rules will be obeyed.

If the class has not been loaded so far, it is being loaded and linked first. This is done through either the specified class loader or one of its parent class loaders. The caller can also request the class to be initialized, which means that a possible static initializer block is executed.

Parameters
className the name of the non-primitive-type class to find.
initializeBoolean indicates whether the class should be initialized.
classLoader the class loader to use to load the class.
Returns
  • the named Class instance.
Throws
ClassNotFoundException if the requested class can not be found.
LinkageError if an error occurs during linkage
ExceptionInInitializerError if an exception occurs during static initialization of a class.

public static Class<?> forName (String className)

Since: API Level 1

Returns a Class object which represents the class with the specified name. The name should be the name of a class as described in the class definition; however, Classes representing primitive types can not be found using this method.

If the class has not been loaded so far, it is being loaded and linked first. This is done through either the class loader of the calling class or one of its parent class loaders. The class is also being initialized, which means that a possible static initializer block is executed.

Parameters
className the name of the non-primitive-type class to find.
Returns
  • the named Class instance.
Throws
ClassNotFoundException if the requested class can not be found.
LinkageError if an error occurs during linkage
ExceptionInInitializerError if an exception occurs during static initialization of a class.

public A getAnnotation (Class<A> annotationType)

Since: API Level 1

public Annotation[] getAnnotations ()

Since: API Level 1

Returns all the annotations of this class. If there are no annotations then an empty array is returned.

Returns
  • a copy of the array containing this class' annotations.
See Also

public String getCanonicalName ()

Since: API Level 1

Returns the canonical name of this class. If this class does not have a canonical name as defined in the Java Language Specification, then the method returns null.

Returns
  • this class' canonical name, or null if it does not have a canonical name.

public ClassLoader getClassLoader ()

Since: API Level 1

Returns the class loader which was used to load the class represented by this Class. Implementations are free to return null for classes that were loaded by the bootstrap class loader. The Android reference implementation, though, returns a reference to an actual representation of the bootstrap class loader.

Returns
  • the class loader for the represented class.
See Also

public Class[]<?> getClasses ()

Since: API Level 1

Returns an array containing Class objects for all public classes and interfaces that are members of this class. This includes public members inherited from super classes and interfaces. If there are no such class members or if this object represents a primitive type then an array of length 0 is returned.

Returns
  • the public class members of the class represented by this object.

public Class<?> getComponentType ()

Since: API Level 1

Returns a Class object which represents the component type if this class represents an array type. Returns null if this class does not represent an array type. The component type of an array type is the type of the elements of the array.

Returns
  • the component type of this class.

public Constructor<T> getConstructor (Class...<?> parameterTypes)

Since: API Level 9

Returns a Constructor object which represents the public constructor matching the specified parameter types.

Parameters
parameterTypes the parameter types of the requested constructor. (Class[]) null is equivalent to the empty array.
Returns
  • the constructor described by parameterTypes.
Throws
NoSuchMethodException if the constructor can not be found.
See Also

public Constructor[]<?> getConstructors ()

Since: API Level 1

Returns an array containing Constructor objects for all public constructors for the class represented by this Class. If there are no public constructors or if this Class represents an array class, a primitive type or void then an empty array is returned.

Returns
  • an array with the public constructors of the class represented by this Class.
See Also

public Annotation[] getDeclaredAnnotations ()

Since: API Level 1

Returns the annotations that are directly defined on the class represented by this Class. Annotations that are inherited are not included in the result. If there are no annotations at all, an empty array is returned.

Returns
  • a copy of the array containing the annotations defined for the class that this Class represents.
See Also

public Class[]<?> getDeclaredClasses ()

Since: API Level 1

Returns an array containing Class objects for all classes and interfaces that are declared as members of the class which this Class represents. If there are no classes or interfaces declared or if this class represents an array class, a primitive type or void, then an empty array is returned.

Returns
  • an array with Class objects for all the classes and interfaces that are used in member declarations.

public Constructor<T> getDeclaredConstructor (Class...<?> parameterTypes)

Since: API Level 9

Returns a Constructor object which represents the constructor matching the specified parameter types that is declared by the class represented by this Class.

Parameters
parameterTypes the parameter types of the requested constructor. (Class[]) null is equivalent to the empty array.
Returns
  • the constructor described by parameterTypes.
Throws
NoSuchMethodException if the requested constructor can not be found.
See Also

public Constructor[]<?> getDeclaredConstructors ()

Since: API Level 1

Returns an array containing Constructor objects for all constructors declared in the class represented by this Class. If there are no constructors or if this Class represents an array class, a primitive type or void then an empty array is returned.

Returns
  • an array with the constructors declared in the class represented by this Class.
See Also

public Field getDeclaredField (String name)

Since: API Level 1

Returns a Field object for the field with the specified name which is declared in the class represented by this Class.

Parameters
name the name of the requested field.
Returns
  • the requested field in the class represented by this class.
Throws
NoSuchFieldException if the requested field can not be found.
See Also

public Field[] getDeclaredFields ()

Since: API Level 1

Returns an array containing Field objects for all fields declared in the class represented by this Class. If there are no fields or if this Class represents an array class, a primitive type or void then an empty array is returned.

Returns
  • an array with the fields declared in the class represented by this class.
See Also

public Method getDeclaredMethod (String name, Class...<?> parameterTypes)

Since: API Level 9

Returns a Method object which represents the method matching the specified name and parameter types that is declared by the class represented by this Class.

Parameters
name the requested method's name.
parameterTypes the parameter types of the requested method. (Class[]) null is equivalent to the empty array.
Returns
  • the method described by name and parameterTypes.
Throws
NoSuchMethodException if the requested constructor can not be found.
NullPointerException if name is null.
See Also

public Method[] getDeclaredMethods ()

Since: API Level 1

Returns an array containing Method objects for all methods declared in the class represented by this Class. If there are no methods or if this Class represents an array class, a primitive type or void then an empty array is returned.

Returns
  • an array with the methods declared in the class represented by this Class.
See Also

public Class<?> getDeclaringClass ()

Since: API Level 1

Returns the declaring Class of this Class. Returns null if the class is not a member of another class or if this Class represents an array class, a primitive type or void.

Returns
  • the declaring Class or null.

public Class<?> getEnclosingClass ()

Since: API Level 1

Returns the enclosing Class of this Class. If there is no enclosing class the method returns null.

Returns
  • the enclosing Class or null.

public Constructor<?> getEnclosingConstructor ()

Since: API Level 1

Gets the enclosing Constructor of this Class, if it is an anonymous or local/automatic class; otherwise null.

Returns
  • the enclosing Constructor instance or null.

public Method getEnclosingMethod ()

Since: API Level 1

Gets the enclosing Method of this Class, if it is an anonymous or local/automatic class; otherwise null.

Returns
  • the enclosing Method instance or null.

public T[] getEnumConstants ()

Since: API Level 1

Gets the enum constants associated with this Class. Returns null if this Class does not represent an enum type.

Returns
  • an array with the enum constants or null.

public Field getField (String name)

Since: API Level 1

Returns a Field object which represents the public field with the specified name. This method first searches the class C represented by this Class, then the interfaces implemented by C and finally the superclasses of C.

Parameters
name the name of the requested field.
Returns
  • the public field specified by name.
Throws
NoSuchFieldException if the field can not be found.
See Also

public Field[] getFields ()

Since: API Level 1

Returns an array containing Field objects for all public fields for the class C represented by this Class. Fields may be declared in C, the interfaces it implements or in the superclasses of C. The elements in the returned array are in no particular order.

If there are no public fields or if this class represents an array class, a primitive type or void then an empty array is returned.

Returns
  • an array with the public fields of the class represented by this Class.
See Also

public Type[] getGenericInterfaces ()

Since: API Level 1

Gets the Types of the interfaces that this Class directly implements. If the Class represents a primitive type or void then an empty array is returned.

Returns
  • an array of Type instances directly implemented by the class represented by this class.

public Type getGenericSuperclass ()

Since: API Level 1

Gets the Type that represents the superclass of this class.

Returns
  • an instance of Type representing the superclass.

public Class[]<?> getInterfaces ()

Since: API Level 1

Returns an array of Class objects that match the interfaces specified in the implements declaration of the class represented by this Class. The order of the elements in the array is identical to the order in the original class declaration. If the class does not implement any interfaces, an empty array is returned.

Returns
  • an array with the interfaces of the class represented by this class.

public Method getMethod (String name, Class...<?> parameterTypes)

Since: API Level 9

Returns a Method object which represents the public method with the specified name and parameter types. This method first searches the class C represented by this Class, then the superclasses of C and finally the interfaces implemented by C and finally the superclasses of C for a method with matching name.

Parameters
name the requested method's name.
parameterTypes the parameter types of the requested method. (Class[]) null is equivalent to the empty array.
Returns
  • the public field specified by name.
Throws
NoSuchMethodException if the method can not be found.
See Also

public Method[] getMethods ()

Since: API Level 1

Returns an array containing Method objects for all public methods for the class C represented by this Class. Methods may be declared in C, the interfaces it implements or in the superclasses of C. The elements in the returned array are in no particular order.

If there are no public methods or if this Class represents a primitive type or void then an empty array is returned.

Returns
  • an array with the methods of the class represented by this Class.
See Also

public int getModifiers ()

Since: API Level 1

Returns an integer that represents the modifiers of the class represented by this Class. The returned value is a combination of bits defined by constants in the Modifier class.

Returns
  • the modifiers of the class represented by this Class.

public String getName ()

Since: API Level 1

Returns the name of the class represented by this Class. For a description of the format which is used, see the class definition of Class.

Returns
  • the name of the class represented by this Class.

public Package getPackage ()

Since: API Level 1

Returns the Package of which the class represented by this Class is a member. Returns null if no Package object was created by the class loader of the class.

Returns
  • Package the Package of which this Class is a member or null.

public ProtectionDomain getProtectionDomain ()

Since: API Level 1

Returns null.

public URL getResource (String resName)

Since: API Level 1

Returns the URL of the resource specified by resName. The mapping between the resource name and the URL is managed by the class' class loader.

Parameters
resName the name of the resource.
Returns
  • the requested resource's URL object or null if the resource can not be found.
See Also

public InputStream getResourceAsStream (String resName)

Since: API Level 1

Returns a read-only stream for the contents of the resource specified by resName. The mapping between the resource name and the stream is managed by the class' class loader.

Parameters
resName the name of the resource.
Returns
  • a stream for the requested resource or null if no resource with the specified name can be found.
See Also

public Object[] getSigners ()

Since: API Level 1

Returns null. (On Android, a ClassLoader can load classes from multiple dex files. All classes from any given dex file will have the same signers, but different dex files may have different signers. This does not fit well with the original ClassLoader-based model of getSigners.)

Returns
  • null.

public String getSimpleName ()

Since: API Level 1

Returns the simple name of the class represented by this Class as defined in the source code. If there is no name (that is, the class is anonymous) then an empty string is returned. If the receiver is an array then the name of the underlying type with square braces appended (for example "Integer[]") is returned.

Returns
  • the simple name of the class represented by this Class.

public Class<? super T> getSuperclass ()

Since: API Level 1

Returns the Class object which represents the superclass of the class represented by this Class. If this Class represents the Object class, a primitive type, an interface or void then the method returns null. If this Class represents an array class then the Object class is returned.

Returns
  • the superclass of the class represented by this Class.

public synchronized TypeVariable[]<Class<T>> getTypeParameters ()

Since: API Level 1

Returns an array containing TypeVariable objects for type variables declared by the generic class represented by this Class. Returns an empty array if the class is not generic.

Returns
  • an array with the type variables of the class represented by this class.

public boolean isAnnotation ()

Since: API Level 1

Indicates whether this Class represents an annotation class.

Returns
  • true if this Class represents an annotation class; false otherwise.

public boolean isAnnotationPresent (Class<? extends Annotation> annotationType)

Since: API Level 1

Indicates whether or not this element has an annotation with the specified annotation type (including inherited annotations).

Parameters
annotationType the type of the annotation to search for
Returns
  • true if the annotation exists, false otherwise

public boolean isAnonymousClass ()

Since: API Level 1

Indicates whether the class represented by this Class is anonymously declared.

Returns
  • true if the class represented by this Class is anonymous; false otherwise.

public boolean isArray ()

Since: API Level 1

Indicates whether the class represented by this Class is an array class.

Returns
  • true if the class represented by this Class is an array class; false otherwise.

public boolean isAssignableFrom (Class<?> cls)

Since: API Level 1

Indicates whether the specified class type can be converted to the class represented by this Class. Conversion may be done via an identity conversion or a widening reference conversion (if either the receiver or the argument represent primitive types, only the identity conversion applies).

Parameters
cls the class to check.
Returns
  • true if cls can be converted to the class represented by this Class; false otherwise.
Throws
NullPointerException if cls is null.

public boolean isEnum ()

Since: API Level 1

Indicates whether the class represented by this Class is an enum.

Returns
  • true if the class represented by this Class is an enum; false otherwise.

public boolean isInstance (Object object)

Since: API Level 1

Indicates whether the specified object can be cast to the class represented by this Class. This is the runtime version of the instanceof operator.

Parameters
object the object to check.
Returns
  • true if object can be cast to the type represented by this Class; false if object is null or cannot be cast.

public boolean isInterface ()

Since: API Level 1

Indicates whether this Class represents an interface.

Returns
  • true if this Class represents an interface; false otherwise.

public boolean isLocalClass ()

Since: API Level 1

Indicates whether the class represented by this Class is defined locally.

Returns
  • true if the class represented by this Class is defined locally; false otherwise.

public boolean isMemberClass ()

Since: API Level 1

Indicates whether the class represented by this Class is a member class.

Returns
  • true if the class represented by this Class is a member class; false otherwise.

public boolean isPrimitive ()

Since: API Level 1

Indicates whether this Class represents a primitive type.

Returns
  • true if this Class represents a primitive type; false otherwise.

public boolean isSynthetic ()

Since: API Level 1

Indicates whether this Class represents a synthetic type.

Returns
  • true if this Class represents a synthetic type; false otherwise.

public T newInstance ()

Since: API Level 1

Returns a new instance of the class represented by this Class, created by invoking the default (that is, zero-argument) constructor. If there is no such constructor, or if the creation fails (either because of a lack of available memory or because an exception is thrown by the constructor), an InstantiationException is thrown. If the default constructor exists but is not accessible from the context where this method is invoked, an IllegalAccessException is thrown.

Returns
  • a new instance of the class represented by this Class.
Throws
IllegalAccessException if the default constructor is not visible.
InstantiationException if the instance can not be created.

public String toString ()

Since: API Level 1

Returns a string containing a concise, human-readable description of this object. Subclasses are encouraged to override this method and provide an implementation that takes into account the object's type and data. The default implementation is equivalent to the following expression: 

   getClass().getName() + '@' + Integer.toHexString(hashCode())

See Writing a useful toString method if you intend implementing your own toString method.

Returns
  • a printable representation of this object.