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Class java.lang.Class
java.lang.Object
|
+----java.lang.Class
- public final class Class
- extends Object
- implements Serializable
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. Finally, the either primitive Java types
(boolean, byte, char, short, int, long, float, and double) and
the keyword void are also represented as Class objects.
There is no public constructor for the class Class.
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());
}
- See Also:
- defineClass
-
forName(String)
- Returns the
Class
object associated with the class
with the given string name.
-
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.
-
getClassLoader()
- Determines the class loader for the class.
-
getComponentType()
- If this class represents an array type, returns the Class
object representing the component type of the array; otherwise
returns null.
-
getConstructor(Class[])
- Returns a Constructor object that reflects the specified public
constructor of the class represented by this Class object.
-
getConstructors()
- Returns an array containing Constructor objects reflecting
all the public constructors of the class represented by this
Class object.
-
getDeclaredClasses()
- Returns an array of Class objects reflecting all the classes
and interfaces declared as members of the class represented by
this Class object.
-
getDeclaredConstructor(Class[])
- Returns a Constructor object that reflects the specified declared
constructor of the class or interface represented by this Class
object.
-
getDeclaredConstructors()
- Returns an array of Constructor objects reflecting all the
constructors declared by the class represented by this Class
object.
-
getDeclaredField(String)
- Returns a Field object that reflects the specified declared
field of the class or interface represented by this Class
object.
-
getDeclaredFields()
- Returns an array of Field objects reflecting all the fields
declared by the class or interface represented by this Class
object.
-
getDeclaredMethod(String, Class[])
- Returns a Method object that reflects the specified declared
method of the class or interface represented by this Class
object.
-
getDeclaredMethods()
- Returns an array of Method objects reflecting all the methods
declared by the class or interface represented by this Class
object.
-
getDeclaringClass()
- If the class or interface represented by this Class object is
a member of another class, returns the Class object
representing the class of which it is a member (its
declaring class).
-
getField(String)
- Returns a Field object that reflects the specified public
member field of the class or interface represented by
this Class object.
-
getFields()
- Returns an array containing Field objects reflecting all the
accessible public fields of the class or interface represented
by this Class object.
-
getInterfaces()
- Determines the interfaces implemented by the class or interface
represented by this object.
-
getMethod(String, Class[])
- Returns a Method object that reflects the specified public
member method of the class or interface represented by this
Class object.
-
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 and those inherited from
superclasses and superinterfaces.
-
getModifiers()
- Returns the Java language modifiers for this class or
interface, encoded in an integer.
-
getName()
- Returns the fully-qualified name of the type (class, interface,
array, or primitive) represented by this Class object, as a String.
-
getResource(String)
-
-
getResourceAsStream(String)
- Find a resource with a given name.
-
getSigners()
- Get the signers of this class.
-
getSuperclass()
- If this object represents any class other than the class
Object, then the object that represents the superclass
of that class is returned.
-
isArray()
- If this Class object represents an array type, returns true,
otherwise returns false.
-
isAssignableFrom(Class)
- 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.
-
isInstance(Object)
- This method is the dynamic equivalent of the Java language
instanceof
operator.
-
isInterface()
- Determines if the specified Class object represents an interface type.
-
isPrimitive()
- Determines if the specified Class object represents a primitive Java
type.
-
newInstance()
- Creates a new instance of a class.
-
toString()
- Converts the object to a string.
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 the fully qualified name of the class.
If this Class object represents a primitive type,
returns the name of the primitive type.
- Returns:
- a string representation of this class object.
- Overrides:
- toString in class Object
forName
public static native Class forName(String className) throws ClassNotFoundException
- Returns the
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. If it
succeeds, returns the Class object representing the class. If
it fails, the method throws a ClassNotFoundException.
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")
- Parameters:
- className - the fully qualified name of the desired class.
- Returns:
- the
Class
descriptor for the class with the
specified name.
- Throws: ClassNotFoundException
- if the class could not be found.
newInstance
public native Object newInstance() throws InstantiationException, IllegalAccessException
- Creates a new instance of a class.
- Returns:
- a newly allocated instance of the class represented by this
object. This is done exactly as if by a
new
expression with an empty argument list.
- Throws: IllegalAccessException
- if the class or initializer is
not accessible.
- Throws: InstantiationException
- if an application tries to
instantiate an abstract class or an interface, or if the
instantiation fails for some other reason.
isInstance
public native boolean isInstance(Object obj)
- 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, returns true if the specified Object argument is an
instance of the represented class (or of any of its
subclasses); false otherwise. If this Class object represents
an array class, returns true if the specified Object argument
can be converted to an object of the array type by an identity
conversion or by a widening reference conversion; false
otherwise. If this Class object represents an interface,
returns true if the class or any superclass of the
specified Object argument implements this interface; false
otherwise. If this Class object represents a primitive type,
returns false.
- Parameters:
- obj - The object to check
isAssignableFrom
public native 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. It returns true
if so, false otherwise. If this Class object represents a
primitive type, returns true if the specified Class parameter
is exactly this Class object, false otherwise.
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.
- Throws: NullPointerException
- if the specified Class parameter is null.
isInterface
public native boolean isInterface()
- Determines if the specified Class object represents an interface type.
- Returns:
-
true
if this object represents an interface;
false
otherwise.
isArray
public native boolean isArray()
- If this Class object represents an array type, returns true,
otherwise returns false.
isPrimitive
public native boolean isPrimitive()
- Determines if the specified Class object represents a primitive Java
type.
There are nine predefined Class objects to represent the eight
primitive Java 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, and void.
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.
- See Also:
- TYPE, TYPE, TYPE, TYPE, TYPE, TYPE, TYPE, TYPE, TYPE
getName
public native String getName()
- Returns the fully-qualified name of the type (class, interface,
array, or primitive) represented by this Class object, as a String.
- Returns:
- the fully qualified name of the class or interface
represented by this object.
getClassLoader
public native ClassLoader getClassLoader()
- Determines the class loader for the class.
- Returns:
- the class loader that created the class or interface
represented by this object, or
null
if the
class was not created by a class loader.
- See Also:
- ClassLoader
getSuperclass
public native Class getSuperclass()
- If this object represents any class other than the class
Object, then the object that represents the superclass
of that class is returned.
If this object is the one that represents the class
Object or this object represents an interface,
null is returned.
- Returns:
- the superclass of the class represented by this object.
getInterfaces
public native Class[] getInterfaces()
- Determines the interfaces implemented by the class or interface
represented by this object.
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.
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 the class or interface implements no interfaces, the method
returns an array of length 0.
- Returns:
- an array of interfaces implemented by this class.
getComponentType
public native Class getComponentType()
- If this class represents an array type, returns the Class
object representing the component type of the array; otherwise
returns null.
- See Also:
- Array
getModifiers
public native int getModifiers()
- Returns the Java language modifiers for this class or
interface, encoded in an integer. The modifiers consist of the
Java Virtual Machine's constants for public, protected,
private, final, and interface; they should be decoded using the
methods of class Modifier.
The modifier encodings are defined in The Java Virtual
Machine Specification, table 4.1.
- See Also:
- Modifier
getSigners
public native Object[] getSigners()
- Get the signers of this class.
getDeclaringClass
public 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 of which it is a member (its
declaring class). Returns null if this class or
interface is not a member of any other class.
getClasses
public 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. This includes public class
and interface members inherited from superclasses and public
class and interface members declared by the class. Returns an
array of length 0 if the class has no public member classes or
interfaces, or if this Class object represents a primitive
type.
getFields
public Field[] getFields() throws SecurityException
- Returns an array containing Field objects reflecting all the
accessible public fields of the class or interface represented
by this Class object. Returns an array of length 0 if the
class or interface has no accessible public fields, or if it
represents an array type or a primitive type.
Specifically, if this Class object represents a class,
returns the public fields of this class and of all its
superclasses. If this Class object represents an interface,
returns the fields of this interface and of all its
superinterfaces. If this Class object represents an array type
or a primitive type, returns an array of length 0.
The implicit length field for array types 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.
- Throws: SecurityException
- if access to the information is denied.
- See Also:
- Field
getMethods
public Method[] getMethods() throws SecurityException
- 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 and those inherited from
superclasses and superinterfaces. Returns an array of length 0
if the class or interface has no public member methods.
See The Java Language Specification, sections 8.2
and 8.4.
- Throws: SecurityException
- if access to the information is denied.
- See Also:
- Method
getConstructors
public Constructor[] getConstructors() throws SecurityException
- Returns an array containing Constructor objects reflecting
all the public constructors of the class represented by this
Class object. An array of length 0 is returned if the class
has no public constructors.
- Throws: SecurityException
- if access to the information is denied.
- See Also:
- Constructor
getField
public Field getField(String name) throws NoSuchFieldException, SecurityException
- Returns a Field object that reflects the specified public
member field of the class or interface represented by
this Class object. The name parameter is a String specifying
the simple name of the desired field.
The field to be reflected is located by searching all the
member fields of the class or interface represented by this
Class object for a public field with the specified name.
See The Java Language Specification, sections 8.2 and 8.3.
- Throws: NoSuchFieldException
- if a field with the specified name is
not found.
- Throws: SecurityException
- if access to the information is denied.
- See Also:
- Field
getMethod
public Method getMethod(String name,
Class parameterTypes[]) throws NoSuchMethodException, SecurityException
- Returns a Method object that reflects the specified public
member method of the class or interface represented by this
Class object. The name parameter is a String specifying the
simple name the desired method, and the parameterTypes
parameter is an array of Class objects that identify the
method's formal parameter types, in declared order.
The method to reflect is located by searching all the member
methods of the class or interface represented by this Class
object for a public method with the specified name and exactly
the same formal parameter types.
See The Java Language Specification, sections 8.2
and 8.4.
- Throws: NoSuchMethodException
- if a matching method is not found.
- Throws: SecurityException
- if access to the information is denied.
- See Also:
- Method
getConstructor
public Constructor getConstructor(Class parameterTypes[]) throws NoSuchMethodException, SecurityException
- Returns a Constructor object that reflects the specified public
constructor of the class represented by this Class object. The
parameterTypes parameter is an array of Class objects that
identify the constructor's formal parameter types, in declared
order.
The constructor to reflect is located by searching all the
constructors of the class represented by this Class object for
a public constructor with the exactly the same formal parameter
types.
- Throws: NoSuchMethodException
- if a matching method is not found.
- Throws: SecurityException
- if access to the information is denied.
- See Also:
- Constructor
getDeclaredClasses
public Class[] getDeclaredClasses() throws SecurityException
- Returns an array of Class objects reflecting all the classes
and interfaces declared as members of the class represented by
this Class object. This includes public, protected, default
(package) access, and private classes and interfaces declared
by the class, but excludes inherited classes and interfaces.
Returns an array of length 0 if the class declares no classes
or interfaces as members, or if this Class object represents a
primitive type.
- Throws: SecurityException
- if access to the information is denied.
getDeclaredFields
public Field[] getDeclaredFields() throws SecurityException
- Returns an array of Field objects reflecting all the fields
declared by the class or interface represented by this Class
object. This includes public, protected, default (package)
access, and private fields, but excludes inherited
fields. Returns an array of length 0 if the class or interface
declares no fields, or if this Class object represents a
primitive type.
See The Java Language Specification, sections 8.2 and
8.3.
- Throws: SecurityException
- if access to the information is denied.
- See Also:
- Field
getDeclaredMethods
public Method[] getDeclaredMethods() throws SecurityException
- Returns an array of Method objects reflecting all the methods
declared by the class or interface represented by this Class
object. This includes public, protected, default (package)
access, and private methods, but excludes inherited
methods. Returns an array of length 0 if the class or interface
declares no methods, or if this Class object represents a
primitive type.
See The Java Language Specification, section 8.2.
- Throws: SecurityException
- if access to the information is denied.
- See Also:
- Method
getDeclaredConstructors
public Constructor[] getDeclaredConstructors() throws SecurityException
- Returns an array of Constructor objects reflecting all the
constructors declared by the class represented by this Class
object. These are public, protected, default (package) access,
and private constructors. Returns an array of length 0 if this
Class object represents an interface or a primitive type.
See The Java Language Specification, section 8.2.
- Throws: SecurityException
- if access to the information is denied.
- See Also:
- Constructor
getDeclaredField
public Field getDeclaredField(String name) throws NoSuchFieldException, SecurityException
- Returns a Field object that reflects the specified declared
field of the class or interface represented by this Class
object. The name parameter is a String that specifies the
simple name of the desired field.
- Throws: NoSuchFieldException
- if a field with the specified name is
not found.
- Throws: SecurityException
- if access to the information is denied.
- See Also:
- Field
getDeclaredMethod
public Method getDeclaredMethod(String name,
Class parameterTypes[]) throws NoSuchMethodException, SecurityException
- Returns a Method object that reflects the specified declared
method of the class or interface represented by this Class
object. The name parameter is a String that specifies the
simple name of the desired method, and the parameterTypes
parameter is an array of Class objects that identify the
method's formal parameter types, in declared order.
- Throws: NoSuchMethodException
- if a matching method is not found.
- Throws: SecurityException
- if access to the information is denied.
- See Also:
- Method
getDeclaredConstructor
public Constructor getDeclaredConstructor(Class parameterTypes[]) throws NoSuchMethodException, SecurityException
- Returns a Constructor object that reflects the specified declared
constructor of the class or interface represented by this Class
object. The parameterTypes parameter is an array of Class
objects that identify the constructor's formal parameter types,
in declared order.
- Throws: NoSuchMethodException
- if a matching method is not found.
- Throws: SecurityException
- if access to the information is denied.
- See Also:
- Constructor
getResourceAsStream
public InputStream getResourceAsStream(String name)
- Find a resource with a given name. Will return null if no
resource with this name is found. The rules for searching a
resources associated with a given class are implemented by the
ClassLoader of the class.
The Class methods delegate to ClassLoader methods, after applying
a naming convention: if the resource name starts with "/", it is used
as is. Otherwise, the name of the package is prepended, after
converting "." to "/".
- See Also:
- ClassLoader
getResource
public URL getResource(String name)
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