javassist.tools.reflect

Class Metaobject

java.lang.Object

javassist.tools.reflect.Metaobject

All Implemented Interfaces:

java.io.Serializable

public class Metaobject
extends java.lang.Object
implements java.io.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

Constructor Summary

Constructors

Constructor and Description
Metaobject(java.lang.Object self, java.lang.Object[] args) Constructs a Metaobject.

Method Summary

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

Methods inherited from class java.lang.Object

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

Constructor Detail

Metaobject

public Metaobject(java.lang.Object self,
                  java.lang.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.

Method Detail

getClassMetaobject

public final ClassMetaobject getClassMetaobject()

Obtains the class metaobject associated with this metaobject.

See Also:

ClassMetaobject

getObject

public final java.lang.Object getObject()

Obtains the object controlled by this metaobject.

setObject

public final void setObject(java.lang.Object self)

Changes the object controlled by this metaobject.

Parameters:

self - the object

getMethodName

public final java.lang.String getMethodName(int identifier)

Returns the name of the method specified by identifier.

getParameterTypes

public final java.lang.Class[] getParameterTypes(int identifier)

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

getReturnType

public final java.lang.Class getReturnType(int identifier)

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

trapFieldRead

public java.lang.Object trapFieldRead(java.lang.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(java.lang.String name,
                           java.lang.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 java.lang.Object trapMethodcall(int identifier,
                                       java.lang.Object[] args)
                                throws java.lang.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:

java.lang.Throwable