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Java Platform 1.2 Beta 4 |
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java.lang.Object | +--java.lang.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 other 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());
}
ClassLoader.defineClass(byte[], int, int), Serialized Form| Field Summary | |
| static ObjectStreamField[] | serialPersistentFields
Class Class is special cased within the Serialization Stream Protocol. |
| Method Summary | |
| static Class | forName(String name,
boolean initialize,
ClassLoader loader)
Given the name of a class a lá getName, this
method loads the class through the specified
ClassLoader. |
| static Class | forName(String className)
Returns the Class object associated with the class
with the given string name.
|
| 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()
If this class represents an array type, returns the Class object representing the component type of the array; otherwise returns null. |
| Constructor | 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. |
| 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 | getDeclaredConstructor(Class[] parameterTypes)
Returns a Constructor object that reflects the specified declared 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 of which it is a member (its declaring class). |
| 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. |
| 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 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 fully-qualified name of the type (class, interface, array, or primitive) represented by this Class object, as a String. |
| Package | getPackage()
Get the package for this class. |
| ProtectionDomain | getProtectionDomain()
Returns the ProtectionDomain of this class. |
| URL | getResource(String name)
|
| InputStream | getResourceAsStream(String name)
Find a resource with a given name. |
| Object[] | getSigners()
Get the signers of this class. |
| 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.
|
| boolean | isArray()
If this Class object represents an array type, returns true, otherwise returns false. |
| 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 | isInstance(Object obj)
This method is the dynamic equivalent of the Java language instanceof operator. |
| boolean | isInterface()
Determines if the specified Class object represents an interface type. |
| boolean | isPrimitive()
Determines if the specified Class object represents a primitive Java type. |
| Object | newInstance()
Creates a new instance of a class. |
| 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 | |
| Field Detail |
public static final ObjectStreamField[] serialPersistentFields
TC_CLASS ClassDescriptor
A ClassDescriptor is a special cased serialization of
a java.io.ObjectStreamClass instance.
A new handle is generated for the initial time the class descriptor
is written into the stream. Future references to the class descriptor
are written as references to the initial class descriptor instance.ObjectStreamClass| Method Detail |
public String toString()
"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.
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, in a
form as returned by getName(), 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")
className
- the fully qualified name of the desired class.Class descriptor for the class with the
specified name.
public static Class forName(String name,
boolean initialize,
ClassLoader loader)
throws ClassNotFoundException
getName, this
method loads the class through the specified
ClassLoader. If, and only if, the initialize
argument is true, this method will link and initialize the
class, if the class has not been initialized earlier.
If parameter loader is null, the class is loaded
through the bootstrap class loader.
For example, in an instance method, the expression:
Class.forName("Foo")
Class.forName("Foo", true, this.getClass().getClassLoader())
name
- name of the desired class
initialize
- whether the class must be initialized
loader
- class loader from which the class must be loadedforName(String),
ClassLoader
public Object newInstance()
throws InstantiationException,
IllegalAccessException
new
expression with an empty argument list.public boolean isInstance(Object obj)
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.
obj
- The object to checkpublic boolean isAssignableFrom(Class cls)
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.
public boolean isInterface()
true if this object represents an interface;
false otherwise.public boolean isArray()
public boolean isPrimitive()
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.
Boolean.TYPE,
Character.TYPE,
Byte.TYPE,
Short.TYPE,
Integer.TYPE,
Long.TYPE,
Float.TYPE,
Double.TYPE,
Void.TYPEpublic String getName()
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 D double F float I int J long Lclassname; class or interface S short Z boolean
public ClassLoader getClassLoader()
null to represent the bootstrap class
loader. This method will return null in such
implementations if this class was loaded by the bootstrap
class loader.
If a security manager is present, this method will succeed only
if the caller's class loader is the same as or is an ancestor of
the class loader for the class. Otherwise, the caller must have
RuntimePermission("getClassLoader") permission
or a SecurityException will be thrown.
ClassLoaderpublic Class getSuperclass()
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.
public Package getPackage()
Packages have attributes for versions and specifications only if the information was defined in the manifests that accompany the classes and if the class loader created the package instance with the attributes from the manifest.
public Class[] getInterfaces()
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.
public Class getComponentType()
Arraypublic int getModifiers()
The modifier encodings are defined in The Java Virtual Machine Specification, table 4.1.
Modifierpublic Object[] getSigners()
public Class getDeclaringClass()
public Class[] getClasses()
public Field[] getFields()
throws SecurityException
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.
Field
public Method[] getMethods()
throws SecurityException
See The Java Language Specification, sections 8.2 and 8.4.
Method
public Constructor[] getConstructors()
throws SecurityException
Constructor
public Field getField(String name)
throws NoSuchFieldException,
SecurityException
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.
Field
public Method getMethod(String name,
Class[] parameterTypes)
throws NoSuchMethodException,
SecurityException
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.
Method
public Constructor getConstructor(Class[] parameterTypes)
throws NoSuchMethodException,
SecurityException
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.
Constructor
public Class[] getDeclaredClasses()
throws SecurityException
public Field[] getDeclaredFields()
throws SecurityException
Field
public Method[] getDeclaredMethods()
throws SecurityException
See The Java Language Specification, section 8.2.
Method
public Constructor[] getDeclaredConstructors()
throws SecurityException
See The Java Language Specification, section 8.2.
Constructor
public Field getDeclaredField(String name)
throws NoSuchFieldException,
SecurityException
Field
public Method getDeclaredMethod(String name,
Class[] parameterTypes)
throws NoSuchMethodException,
SecurityException
Method
public Constructor getDeclaredConstructor(Class[] parameterTypes)
throws NoSuchMethodException,
SecurityException
Constructorpublic InputStream getResourceAsStream(String name)
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 "/".
ClassLoaderpublic URL getResource(String name)
public ProtectionDomain getProtectionDomain()
RuntimePermission("getProtectionDomain") permission
to ensure the caller has permission to get the
ProtectionDomain.ProtectionDomain,
RuntimePermission
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Java Platform 1.2 Beta 4 |
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