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   , GenericDeclaration   , Type   , AnnotatedElement   

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());
 

Since:

JDK1.0

See Also:

ClassLoader.defineClass(byte[], int, int) , Serialized Form

Method Summary

<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 > A	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 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 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

toString

public String    toString()

Converts the object to a string. The string representation is the string "class" or "interface", followed by a space, and then by the fully qualified name of the class in the format returned by getName. If this Class object represents a primitive type, this method returns the name of the primitive type. If this Class object represents void this method returns "void".

Overrides:

toString in class Object

Returns:

a string representation of this class object.

forName

public static Class   <?> forName(String    className)
                        throws ClassNotFoundException   

Returns the Class object associated with the class or interface with the given string name. Invoking this method is equivalent to:

  Class.forName(className, true, currentLoader)
 

where currentLoader denotes the defining class loader of the current class.

For example, the following code fragment returns the runtime Class descriptor for the class named java.lang.Thread:

   Class t = Class.forName("java.lang.Thread")
 

A call to forName("X") causes the class named X to be initialized.

Parameters:

className - the fully qualified name of the desired class.

Returns:

the Class object for the class with the specified name.

Throws:

LinkageError - if the linkage fails

ExceptionInInitializerError - if the initialization provoked by this method fails

ClassNotFoundException - if the class cannot be located

forName

public static Class   <?> forName(String    name,
                               boolean initialize,
                               ClassLoader    loader)
                        throws ClassNotFoundException   

Returns the Class object associated with the class or interface with the given string name, using the given class loader. Given the fully qualified name for a class or interface (in the same format returned by getName) this method attempts to locate, 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.

Parameters:

name - fully qualified name of the desired class

initialize - whether the class must be initialized

loader - class loader from which the class must be loaded

Returns:

class object representing the desired class

Throws:

LinkageError - if the linkage fails

ExceptionInInitializerError - if the initialization provoked by this method fails

ClassNotFoundException - if the class cannot be located by the specified class loader

Since:

1.2

See Also:

forName(String) , ClassLoader

newInstance

public