javassist.tools.reflect

Class Metaobject

java.lang.Object

javassist.tools.reflect.Metaobject

All Implemented Interfaces:

Serializable

public class Metaobject
extends Object
implements Serializable

A runtime metaobject.

A Metaobject is created for every object at the base level. A different reflective object is associated with a different metaobject.

The metaobject intercepts method calls on the reflective object at the base-level. To change the behavior of the method calls, a subclass of Metaobject should be defined.

To obtain a metaobject, calls _getMetaobject() on a reflective object. For example,

Metaobject m = ((Metalevel)reflectiveObject)._getMetaobject();
 

See Also:

ClassMetaobject, Metalevel, Serialized Form

Field Summary

Fields

Modifier and Type	Field and Description
protected Metalevel	baseobject
protected ClassMetaobject	classmetaobject
protected Method[]	methods

Constructor Summary

Constructors

Modifier	Constructor and Description
protected	Metaobject() Constructs a Metaobject without initialization.
	Metaobject(Object self, Object[] args) Constructs a Metaobject.

Method Summary

Methods

Modifier and Type	Method and Description
ClassMetaobject	getClassMetaobject() Obtains the class metaobject associated with this metaobject.
String	getMethodName(int identifier) Returns the name of the method specified by identifier.
Object	getObject() Obtains the object controlled by this metaobject.
Class[]	getParameterTypes(int identifier) Returns an array of Class objects representing the formal parameter types of the method specified by identifier.
Class	getReturnType(int identifier) Returns a Class objects representing the return type of the method specified by identifier.
void	setObject(Object self) Changes the object controlled by this metaobject.
Object	trapFieldRead(String name) Is invoked when public fields of the base-level class are read and the runtime system intercepts it.
void	trapFieldWrite(String name, Object value) Is invoked when public fields of the base-level class are modified and the runtime system intercepts it.
Object	trapMethodcall(int identifier, Object[] args) Is invoked when base-level method invocation is intercepted.

Methods inherited from class java.lang.Object

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

Field Detail

classmetaobject

protected ClassMetaobject classmetaobject

baseobject

protected Metalevel baseobject

methods

protected Method[] methods

Constructor Detail

Metaobject

public Metaobject(Object self,
          Object[] args)

Constructs a Metaobject. The metaobject is constructed before the constructor is called on the base-level object.

Parameters:

self - the object that this metaobject is associated with.

args - the parameters passed to the constructor of self.

Metaobject

protected Metaobject()

Constructs a Metaobject without initialization. If calling this constructor, a subclass should be responsible for initialization.

Method Detail

getClassMetaobject

public final ClassMetaobject getClassMetaobject()

Obtains the class metaobject associated with this metaobject.

See Also:

ClassMetaobject

getObject

public final Object getObject()

Obtains the object controlled by this metaobject.

setObject

public final void setObject(Object self)

Changes the object controlled by this metaobject.

Parameters:

self - the object

getMethodName

public final String getMethodName(int identifier)

Returns the name of the method specified by identifier.

getParameterTypes

public final Class[] getParameterTypes(int identifier)

Returns an array of Class objects representing the formal parameter types of the method specified by identifier.

getReturnType

public final Class getReturnType(int identifier)

Returns a Class objects representing the return type of the method specified by identifier.

trapFieldRead

public Object trapFieldRead(String name)

Is invoked when public fields of the base-level class are read and the runtime system intercepts it. This method simply returns the value of the field.

Every subclass of this class should redefine this method.

trapFieldWrite

public void trapFieldWrite(String name,
                  Object value)

Is invoked when public fields of the base-level class are modified and the runtime system intercepts it. This method simply sets the field to the given value.

Every subclass of this class should redefine this method.

trapMethodcall

public Object trapMethodcall(int identifier,
                    Object[] args)
                      throws Throwable

Is invoked when base-level method invocation is intercepted. This method simply executes the intercepted method invocation with the original parameters and returns the resulting value.

Every subclass of this class should redefine this method.

Note: this method is not invoked if the base-level method is invoked by a constructor in the super class. For example,

abstract class A {
   abstract void initialize();
   A() {
       initialize();    // not intercepted
   }
 }

 class B extends A {
   void initialize() { System.out.println("initialize()"); }
   B() {
       super();
       initialize();    // intercepted
   }
 }

if an instance of B is created, the invocation of initialize() in B is intercepted only once. The first invocation by the constructor in A is not intercepted. This is because the link between a base-level object and a metaobject is not created until the execution of a constructor of the super class finishes.

Throws:

Throwable