Package java.lang

Class Class<T>

java.lang.Object
java.lang.Class<T>
All Implemented Interfaces:
Serializable, AnnotatedElement, GenericDeclaration, Type
public final class Class<T>
extends Object
implements Serializable, AnnotatedElement, GenericDeclaration, Type
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!)
See Also:
Serialized Form

  • Method Summary

    Modifier and Type Method Description
    <U> Class<? extends U> asSubclass​(Class<U> c)
    Casts this Class to represent a subclass of the given class.
    T cast​(Object obj)
    Casts the given 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)
    Returns a Class object which represents the class with the given name.
    static Class<?> forName​(String className, boolean shouldInitialize, ClassLoader classLoader)
    Returns a Class object which represents the class with the given name.
    <A extends Annotation>
    A    		 getAnnotation​(Class<A> annotationType)
    Returns, for this element, the annotation with the specified type, or null if no annotation with the specified type is present (including inherited annotations).
    Annotation[] getAnnotations()
    Returns an array containing all the annotations of this class.
    String getCanonicalName()
    Returns the canonical name of this class.
    Class<?>[] getClasses()
    Returns an array containing Class objects for all public classes and interfaces that are members of this class.
    ClassLoader getClassLoader()
    Returns the class loader which was used to load the class represented by 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 given parameter types.
    Constructor<?>[] getConstructors()
    Returns an array containing Constructor objects for all public constructors for 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 given 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 given 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 given 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()
    Returns the enclosing Constructor of this Class, if it is an anonymous or local/automatic class; otherwise null.
    Method getEnclosingMethod()
    Returns the enclosing Method of this Class, if it is an anonymous or local/automatic class; otherwise null.
    T[] getEnumConstants()
    Returns the enum constants associated with this Class.
    Field getField​(String name)
    Returns a Field object which represents the public field with the given name.
    Field[] getFields()
    Returns an array containing Field objects for all public fields for the class C represented by this Class.
    Type[] getGenericInterfaces()
    Returns the Types of the interfaces that this Class directly implements.
    Type getGenericSuperclass()
    Returns the Type that represents the superclass of this class.
    Class<?>[] getInterfaces()
    Returns an array of Class objects that match the interfaces 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 given 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 resourceName)
    Returns the URL of the given resource, or null if the resource is not found.
    InputStream getResourceAsStream​(String resourceName)
    Returns a read-only stream for the contents of the given resource, or null if the resource is not found.
    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.
    TypeVariable<Class<T>>[] getTypeParameters()
    Returns an array containing TypeVariable objects for type variables declared by the generic class represented by this Class.
    boolean isAnnotation()
    Tests 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()
    Tests whether the class represented by this Class is anonymous.
    boolean isArray()
    Tests whether the class represented by this Class is an array class.
    boolean isAssignableFrom​(Class<?> c)
    Tests whether the given class type can be converted to the class represented by this Class.
    boolean isEnum()
    Tests whether the class represented by this Class is an enum.
    boolean isInstance​(Object object)
    Tests whether the given object can be cast to the class represented by this Class.
    boolean isInterface()
    Tests whether this Class represents an interface.
    boolean isLocalClass()
    Tests whether the class represented by this Class is defined locally.
    boolean isMemberClass()
    Tests whether the class represented by this Class is a member class.
    boolean isPrimitive()
    Tests whether this Class represents a primitive type.
    boolean isSynthetic()
    Tests 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.

    Methods inherited from class java.lang.Object

    clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

  • Method Details

    • forName

      public static Class<?> forName​(String className) throws ClassNotFoundException
      Returns a Class object which represents the class with the given name. The name should be the name of a non-primitive class, as described in the class definition. Primitive types can not be found using this method; use int.class or Integer.TYPE instead.

      If the class has not yet been loaded, it is loaded and initialized first. This is done through either the class loader of the calling class or one of its parent class loaders. It is possible that a static initializer is run as a result of this call.

      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.

    • forName

      public static Class<?> forName​(String className, boolean shouldInitialize, ClassLoader classLoader) throws ClassNotFoundException
      Returns a Class object which represents the class with the given name. The name should be the name of a non-primitive class, as described in the class definition. Primitive types can not be found using this method; use int.class or Integer.TYPE instead.

      If the class has not yet been loaded, it is loaded first, using the given class loader. If the class has not yet been initialized and shouldInitialize is true, the class will be initialized.

      Parameters:
      className - the name of the non-primitive-type class to find.
      shouldInitialize - 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.

    • getClasses

      public Class<?>[] getClasses()
      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.

    • getAnnotation

      public <A extends Annotation> A getAnnotation​(Class<A> annotationType)
      Description copied from interface: AnnotatedElement
      Returns, for this element, the annotation with the specified type, or null if no annotation with the specified type is present (including inherited annotations).
      Specified by:
      getAnnotation in interface AnnotatedElement
      Parameters:
      annotationType - the type of the annotation to search for
      Returns:
      the annotation with the specified type or null

    • getAnnotations

      public Annotation[] getAnnotations()
      Returns an array containing all the annotations of this class. If there are no annotations then an empty array is returned.
      Specified by:
      getAnnotations in interface AnnotatedElement
      Returns:
      an array of all annotations for this element
      See Also:
      getDeclaredAnnotations()

    • getCanonicalName

      public String getCanonicalName()
      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.

    • getClassLoader

      public ClassLoader getClassLoader()
      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, always returns a reference to an actual class loader.

    • getComponentType

      public Class<?> getComponentType()
      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.

    • getConstructor

      public Constructor<T> getConstructor​(Class<?>... parameterTypes) throws NoSuchMethodException
      Returns a Constructor object which represents the public constructor matching the given parameter types. (Class[]) null is equivalent to the empty array.

      See getMethod(java.lang.String, java.lang.Class<?>...) for details of the search order. Use getDeclaredConstructor(java.lang.Class<?>...) if you don't want to search superclasses.

      Throws:
      NoSuchMethodException - if the constructor can not be found.

    • getConstructors

      public Constructor<?>[] getConstructors()
      Returns an array containing Constructor objects for all public constructors for 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.
      See Also:
      getDeclaredConstructors()

    • getDeclaredAnnotations

      public Annotation[] getDeclaredAnnotations()
      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.
      Specified by:
      getDeclaredAnnotations in interface AnnotatedElement
      Returns:
      an array of annotations declared for this element
      See Also:
      getAnnotations()

    • getDeclaredClasses

      public 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. 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.

    • getDeclaredConstructor

      public Constructor<T> getDeclaredConstructor​(Class<?>... parameterTypes) throws NoSuchMethodException
      Returns a Constructor object which represents the constructor matching the given parameter types that is declared by the class represented by this Class. (Class[]) null is equivalent to the empty array.

      Use getConstructor(java.lang.Class<?>...) if you want to search superclasses.

      Throws:
      NoSuchMethodException - if the requested constructor can not be found.

    • getDeclaredConstructors

      public Constructor<?>[] getDeclaredConstructors()
      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.
      See Also:
      getConstructors()

    • getDeclaredField

      public Field getDeclaredField​(String name) throws NoSuchFieldException
      Returns a Field object for the field with the given name which is declared in the class represented by this Class.
      Throws:
      NoSuchFieldException - if the requested field can not be found.
      See Also:
      getField(String)

    • getDeclaredFields

      public Field[] getDeclaredFields()
      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.
      See Also:
      getFields()

    • getDeclaredMethod

      public Method getDeclaredMethod​(String name, Class<?>... parameterTypes) throws NoSuchMethodException
      Returns a Method object which represents the method matching the given name and parameter types that is declared by the class represented by this Class. (Class[]) null is equivalent to the empty array.

      See getMethod(java.lang.String, java.lang.Class<?>...) if you want to search superclasses.

      Throws:
      NoSuchMethodException - if the requested method can not be found.
      NullPointerException - if name is null.

    • getDeclaredMethods

      public Method[] getDeclaredMethods()
      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.
      See Also:
      getMethods()

    • getDeclaringClass

      public Class<?> getDeclaringClass()
      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.

    • getEnclosingClass

      public Class<?> getEnclosingClass()
      Returns the enclosing Class of this Class. If there is no enclosing class the method returns null.

    • getEnclosingConstructor

      public Constructor<?> getEnclosingConstructor()
      Returns the enclosing Constructor of this Class, if it is an anonymous or local/automatic class; otherwise null.

    • getEnclosingMethod

      public Method getEnclosingMethod()
      Returns the enclosing Method of this Class, if it is an anonymous or local/automatic class; otherwise null.

    • getEnumConstants

      public T[] getEnumConstants()
      Returns the enum constants associated with this Class. Returns null if this Class does not represent an enum type.

    • getField

      public Field getField​(String name) throws NoSuchFieldException
      Returns a Field object which represents the public field with the given name. This method first searches the class C represented by this Class, then the interfaces implemented by C and finally the superclasses of C.
      Throws:
      NoSuchFieldException - if the field can not be found.
      See Also:
      getDeclaredField(String)

    • getFields

      public Field[] getFields()
      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.

      See Also:
      getDeclaredFields()

    • getGenericInterfaces

      public Type[] getGenericInterfaces()
      Returns 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.

    • getGenericSuperclass

      public Type getGenericSuperclass()
      Returns the Type that represents the superclass of this class.

    • getInterfaces

      public Class<?>[] getInterfaces()
      Returns an array of Class objects that match the interfaces 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.

    • getMethod

      public Method getMethod​(String name, Class<?>... parameterTypes) throws NoSuchMethodException
      Returns a Method object which represents the public method with the given name and parameter types. (Class[]) null is equivalent to the empty array.

      This method first searches the class C represented by this Class, then the superclasses of C, and finally the interfaces implemented by C and its superclasses.

      Use getDeclaredMethod(java.lang.String, java.lang.Class<?>...) if you don't want to search superclasses.

      Throws:
      NoSuchMethodException - if the method can not be found.

    • getMethods

      public Method[] getMethods()
      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.

      See Also:
      getDeclaredMethods()

    • getModifiers

      public int getModifiers()
      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.

    • getName

      public String getName()
      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.

    • getSimpleName

      public String getSimpleName()
      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.

    • getProtectionDomain

      public ProtectionDomain getProtectionDomain()
      Returns null.

    • getResource

      public URL getResource​(String resourceName)
      Returns the URL of the given resource, or null if the resource is not found. The mapping between the resource name and the URL is managed by the class' class loader.
      See Also:
      ClassLoader

    • getResourceAsStream

      public InputStream getResourceAsStream​(String resourceName)
      Returns a read-only stream for the contents of the given resource, or null if the resource is not found. The mapping between the resource name and the stream is managed by the class' class loader.
      See Also:
      ClassLoader

    • getSigners

      public Object[] getSigners()
      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.)

    • getSuperclass

      public Class<? super T> getSuperclass()
      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.

    • getTypeParameters

      public TypeVariable<Class<T>>[] getTypeParameters()
      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.
      Specified by:
      getTypeParameters in interface GenericDeclaration
      Returns:
      the declared type parameters in declaration order

    • isAnnotation

      public boolean isAnnotation()
      Tests whether this Class represents an annotation class.

    • isAnnotationPresent

      public boolean isAnnotationPresent​(Class<? extends Annotation> annotationType)
      Description copied from interface: AnnotatedElement
      Indicates whether or not this element has an annotation with the specified annotation type (including inherited annotations).
      Specified by:
      isAnnotationPresent in interface AnnotatedElement
      Parameters:
      annotationType - the type of the annotation to search for
      Returns:
      true if the annotation exists, false otherwise

    • isAnonymousClass

      public boolean isAnonymousClass()
      Tests whether the class represented by this Class is anonymous.

    • isArray

      public boolean isArray()
      Tests whether the class represented by this Class is an array class.

    • isAssignableFrom

      public boolean isAssignableFrom​(Class<?> c)
      Tests whether the given 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).
      Throws:
      NullPointerException - if c is null.

    • isEnum

      public boolean isEnum()
      Tests whether the class represented by this Class is an enum.

    • isInstance

      public boolean isInstance​(Object object)
      Tests whether the given object can be cast to the class represented by this Class. This is the runtime version of the instanceof operator.
      Returns:
      true if object can be cast to the type represented by this Class; false if object is null or cannot be cast.

    • isInterface

      public boolean isInterface()
      Tests whether this Class represents an interface.

    • isLocalClass

      public boolean isLocalClass()
      Tests whether the class represented by this Class is defined locally.

    • isMemberClass

      public boolean isMemberClass()
      Tests whether the class represented by this Class is a member class.

    • isPrimitive

      public boolean isPrimitive()
      Tests whether this Class represents a primitive type.

    • isSynthetic

      public boolean isSynthetic()
      Tests whether this Class represents a synthetic type.

    • newInstance

      public T newInstance() throws InstantiationException, IllegalAccessException
      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.
      Throws:
      IllegalAccessException - if the default constructor is not visible.
      InstantiationException - if the instance can not be created.

    • toString

      public String toString()
      Description copied from class: Object
      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.

      Overrides:
      toString in class Object
      Returns:
      a printable representation of this object.

    • getPackage

      public Package getPackage()
      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.

    • desiredAssertionStatus

      public boolean desiredAssertionStatus()
      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.

    • asSubclass

      public <U> Class<? extends U> asSubclass​(Class<U> c)
      Casts this Class to represent a subclass of the given class. If successful, this Class is returned; otherwise a ClassCastException is thrown.
      Throws:
      ClassCastException - if this Class cannot be cast to the given type.

    • cast

      public T cast​(Object obj)
      Casts the given object to the type represented by this Class. If the object is null then the result is also null.
      Throws:
      ClassCastException - if the object cannot be cast to the given type.