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java.lang.Objectjava.lang.Class<T>
T
- the type of the class modeled by this Class
object. For
example, the type of String.class
is Class<String>
.
Use Class<?>
if the class being modeled is unknown.@TransactionType(value=NOT_SUPPORTED) public final class Class<T>
Instances of the class Class
represent classes and interfaces
in a running Java application. 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.
Class
has no public constructor. Instead Class
objects are constructed automatically by the Java Virtual Machine as classes
are loaded.
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()); }
Method Summary | |
---|---|
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 with
the given string name. |
String |
getName()
Returns the fully-qualified name of the entity (class, interface, array class, primitive type, or void) represented by this Class
object, as a String . |
InputStream |
getResourceAsStream(String name)
Finds a resource with a given name from the search path used to load this Class instance. |
Class<? super T> |
getSuperclass()
Returns the Class representing the superclass of the
entity (class, interface, primitive type or void) represented by this
Class . |
boolean |
isAnnotation()
Returns true if this Class object represents an annotation type. |
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. |
T |
newInstance()
Creates a new instance of a class. |
String |
toString()
Converts the object to a string. |
Methods inherited from class java.lang.Object |
---|
equals, getClass, hashCode, notify, notifyAll, wait, wait, wait |
Method Detail |
---|
public String toString()
getName
. If this Class
object represents a
primitive type, this method returns the name of the primitive type. If
this Class
object represents void this method returns
"void".
toString
in class Object
public static Class<?> forName(String className) throws ClassNotFoundException
Class
object associated with the class with
the given string name. Given the fully-qualified name for a class or
interface, this method attempts to locate, load and link the 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")
className
- the fully qualified name of the desired class.
Class
object for the class with the specified
name.
ClassNotFoundException
- if the class could not be found.
SecurityException
- if the permission to dynamically load the class is not
granted.
Error
- if the function fails for any other reason.public T newInstance() throws InstantiationException, IllegalAccessException
new
expression with an empty argument list.
IllegalAccessException
- if the class or initializer is not accessible.
InstantiationException
- if an application tries to instantiate an abstract class
or an interface, or if the instantiation fails for some
other reason.public boolean isInstance(Object obj)
Object
is
assignment-compatible with the object represented by this
Class
. This method is the dynamic equivalent of the Java
language instanceof
operator. The method returns
true
if the specified Object
argument is
non-null and can be cast to the reference type represented by this
Class
object without raising a
ClassCastException.
It returns false
otherwise.
Specifically, if this Class
object represents a declared
class, this method returns true
if the specified
Object
argument is an instance of the represented class
(or of any of its subclasses); it returns false
otherwise.
If this Class
object represents an array class, this
method returns true
if the specified Object
argument can be converted to an object of the array class by an identity
conversion or by a widening reference conversion; it returns
false
otherwise. If this Class
object
represents an interface, this method returns true
if the
class or any superclass of the specified Object
argument
implements this interface; it returns false
otherwise. If
this Class
object represents a primitive type, this method
returns false
.
obj
- the object to check
obj
is an instance of this classpublic boolean isAssignableFrom(Class<?> cls)
Class
object is either the same as, or is a superclass or
superinterface of, the class or interface represented by the specified
Class
parameter. It returns true
if so;
otherwise it returns false
. If this Class
object represents a primitive type, this method returns true
if the specified Class
parameter is exactly this
Class
object; otherwise it returns false
.
Specifically, this method tests whether the type represented by the
specified Class
parameter can be converted to the type
represented by this Class
object via an identity
conversion or via a widening reference conversion. See
The Java Language
Specification, sections 5.1.1 and 5.1.4 ,
for details.
cls
- the Class
object to be checked
boolean
value indicating whether objects of
the type cls
can be assigned to objects of this
class
NullPointerException
- if the specified Class parameter is null.public boolean isInterface()
Class
object represents an
interface type.
true
if this object represents an interface;
false
otherwise.public boolean isAnnotation()
isInterface()
would
also return true, as all annotation types are also interfaces.
public boolean isEnum()
public boolean isArray()
Class
object represents an array class.
true
if this object represents an array class;
false
otherwise.public String getName()
Class
object, as a String
.
If this Class
object represents a class of arrays, then
the internal form of the name consists of the name of the element type in
Java signature format, preceded by one or more "["
characters representing the depth of array nesting. Thus:
returns "(new Object[3]).getClass().getName()
[Ljava.lang.Object;
" and:
returns "(new int[3][4][5][6][7][8][9]).getClass().getName()
[[[[[[[I
". The encoding of element type names
is as follows:
The class or interface name classname is given in fully qualified form as shown in the example above.B byte C char I int J long L<i>classname;</i> class or interface S short Z boolean
public InputStream getResourceAsStream(String name)
Class
instance. This
method returns null
if no resource with this name is found.
The resource names can be represented in two different formats: absolute or relative.
Absolute format:
/packagePathName/resourceName
Relative format:
resourceName
In the absolute format, the programmer provides a fully qualified name that includes both the full path and the name of the resource inside the JAR file. In the path names, the character "/" is used as the separator.
In the relative format, the programmer provides only the name of the
actual resource. Relative names are converted to absolute names by the
system by prepending the resource name with the fully qualified package
name of class upon which the getResourceAsStream
method
was called.
The rules for searching resources associated with a given class are described in chapter 6 of Runtime Environment Specification for the Java Card Platform, Connected Edition.
name
- name of the desired resource
java.io.InputStream
object.
NullPointerException
- if the specified name parameter is null.public boolean desiredAssertionStatus()
public Class<? super T> getSuperclass()
Class
representing the superclass of the
entity (class, interface, primitive type or void) represented by this
Class
. If this Class
represents either the
Object
class, an interface, a primitive type, or void,
then null is returned. If this object represents an array class then the
Class
object representing the Object
class
is returned.
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