Using reflection api to copy like named attributes of a class

Hi guys,
I have been hearing about this for a long time now. How can one copy like named attributes from one class to another using the reflection api??
Can anyone provide a small example, with code??
Thanks.

maxim.veksler wrote:
I think that a chronological order of events should describe what happened :
Issue #1 10:55 15/09/2008 - I try to find a solution to retrieving annotations of a field http://forums.sun.com/thread.jspa?threadID=5331440
Issue #211:13 15/09/2008 - I learn that this can be done using the Field class, so I got looking for a way to getting all the fields http://forums.sun.com/thread.jspa?threadID=5331441
Issue #3 13:15 15/09/2008 - I find a solution which is nearly working and post the last issue I have. http://forums.sun.com/thread.jspa?threadID=5331475
Issue #313:26 15/09/2008 - thomas.behr helps me with the issue mentioned from thread 5331475 http://forums.sun.com/thread.jspa?messageID=10424090#10424090
Issue #2 14:32 15/09/2008 - You (kajbj) comment that I need to use suggested solution. Please note that when I posted this I didn't know about the "right" solution.
Issue #2 15:01 15/09/2008 - I thank you and link to an example where I implemented the search. I still don't know if the solution I found was the correct one.
Please understand that I had no intention to create unnecessary hassle.kaj post above came at 11:32 (according to the time display here), and your post, in the other thread, acknowledging that you now had a solution was at 10:37. So how did you "not know" at that time, that you had a solution.
But nevermind, dead conversation anyway, the post would not have been made under any other circumstances than the present (if then) anyway, and we both know it.
Edit: And I didn't say you had any intention of purposely wasting people's time, but I don't believe that you had any intentions of not doing so, either (i.e. as in trying to prevent it).

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Reflection API in EJB

Hi,
In my BMP, i am doing some validation using Reflection API.
I want to know whether Reflection API put some extra burden on EJB.
Also i am confused how exactly reflection is carried out.
In general i know that it Introspects class and gives all information about class. BUT exactly in what manner.
I have info of how i can use reflection, Like I can get Class , get Object , get Method , Invoke Method , Field , set or get field values etc.
But what i am confused about its cost.
Why reflection API is costly?
So please tell me exact procedure followed OR exact Algorithm used inside Reflection API.
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method call on object without reflection
VS
method call usinf invoke() method on Method class using reflection API.
Thanks,
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simple method call is statically bind during compilation and various checks can be done at this level which helps in avoiding runtime errors during execution.
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--Ashwani

XML document creation using reflection

Hi all,
I'm tyring to write a class which creates an XML document from objects passed in. For example, you call the add(Object) method and it takes your object, uses reflection, then outputs XML like this...
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The only problem is that after looking through this forum I am a little concerned about the performance of my proposed solution (using reflection).
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Thanks,
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The only problem is that after looking through this
forum I am a little concerned about the performance of
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This class is going to be used by multiple batch
processes hence there will be lots of different object
types passed (they'll also be new ones in the future
that we don't even know about yet) hence my reflection
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Using reflection...

Hi,
I have one class. to run that, I am calling like the following...
java -classpath ;.;\comdotebo; com.pack1.MyClass
now I want to take the reference of this class(dynamically) using reflection pakcage like the following...
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but to take the class reference I need to set the classpath;
so how can i set the classpath dynamically.
please give proper solution
thanks
Raja Ramesh Kumar M

here the case is we know both the class and the class path at run time only
for ex: see the following.....
I have two files .....
1) c:\dir1\com\pack1\MyClass1.class
2) c:\dir2\com\pack2\MyClass2.class
now I want to access both the classes using reflection from ...
c:\dir3\com\pack3\MainClass.class
using reflection, we can write the following...
Class clas1 = Class.forName("com.pack1.MyClass1");
if I am taking like this, then I am getting ClassNotFoundException.
becoz, for that we have to give the proper classpath before running the program.
like.
set classpath=%classpath%;.;c:\dir1;
but my problem is here I know the the class name (for ex: com.pack1.MyClass1) and the classpath (ex: c:\dir1)
at runtime only.
so please tell me how to solve this problem
regards
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Using Reflection can we find out details of inner classes in a class

Hello All,
Thanx in advance.
I intend to figure out the name of the inner class and methods declared inside it. How can this be done using reflection API's.
I need the above information to make an automated java doc creation tool for the project I am working in.
Thanx again...
VIkas

Thanx silkm,
Actually suggestion # 1 I have already tried. I used
getClasses() method which returned me a Class[] of
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As contrasted to that, getDeclaredXXX() methods can return all XXX things (including private) but only declared by the target class (not inherited).
You got an empty result back in your case most likely because all your nested/inner classes were non-public. Use getDeclaredClasses() instead.
As to suggestion # 2, the exercise I am doing is a
step before using the java doc tool. One has to insert
a javadoc comment before the method begins in order to
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I'm not using any Xtras or anything, I think this is just embed within the Director builds.
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Hi,
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Download Adobe AIR SDK
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Hi,
I am facing the following problem
I have an Employee class its overridden the following below methods
private void readObject(java.io.ObjectInputStream inStream) {
     inStream.defaultReadObject();
I am trying to call this method using reflection.
my code is like this
     Class fis= Class.forName("java.io.FileInputStream");
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     Object fisObj = fcons.newInstance(new Object[]{"C:\\NewEmployee.ser"});
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The above code is call the readObject method, but it is failing while executing inStream.defaultReadObject() statement
I am getting the following exception
java.lang.reflect.InvocationTargetException
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:39)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:25)
at java.lang.reflect.Method.invoke(Method.java:585)
at HackEmployee.reflect(HackEmployee.java:49)
at HackEmployee.main(HackEmployee.java:131)
Caused by: java.io.NotActiveException: not in call to readObject
at java.io.ObjectInputStream.defaultReadObject(ObjectInputStream.java:474)
at Employee.readObject(Employee.java:77)
... 6 more
can anybody help me?
~ murali

Hi,
Here is the simple example.
public class Employee implements Serializable {
static final long serialVersionUID = 1L;
static final int _VERSION = 2;
private int eno;
private String empName;
     private String paaword;
     private void readObject(java.io.ObjectInputStream inStream)
throws IOException, ClassNotFoundException {
     int version = 0;
     BufferedInputStream bis = new BufferedInputStream(inStream);
     bis.mark(256);
     DataInputStream dis = new DataInputStream(bis);
     try {
          version = dis.readInt();
          Debug.println(Debug.INFO, _TAG, "Loading version=" + version);
     } catch(Exception e) {
          dis.reset();
     switch(version) {
          case 0:
          case 1:
               inStream.defaultReadObject();
               migrateDefaultEmployeeToEncryptionPassword();
               break;
          case _VERSION:
               inStream.defaultReadObject();
               break;
          default:
               throw new IOException("Unknown Version :" + version);
     private void writeObject(ObjectOutputStream aOutputStream)
throws IOException {
     aOutputStream.writeInt(_VERSION);
     aOutputStream.defaultWriteObject();
Now I am writing a tool that need to read data and print all the field and values in a file.
So I am trying the same with reflecton by calling readObject(ObjectInputStream inStream).
But here I am facing the problem, it is geving java.lang.reflect.InvocationTargetException while calling migrateDefaultEmployeeToEncryptionPassword(.
Hope you got my exact scenerio.
Thanks for your replay
~ Murali

Typecasting using Reflection

Hi !
How do I type cast classes using reflection?
I use my own classloader and load a few classes, say 'myinterface', 'myinterfaceimpl' and 'someclass' in that custom classloader.
'myinterface' class is public where as the implementation class, 'myinterfaceimpl', access is private. 'someclass' has a method whose return type is 'myinterface', and it returns an object of instance 'myinterfaceimpl' (which is an innerclass).
1. My application starts with the system classpath (where the above 3 classes are not present).
2. My classloader loads these 3 classes.
3. Using reflection, I invoke the specified method in 'someclass', whose return type is 'myinterface'.
4. Now I am unable to invoke a public method defined in the interface, since the implementation class level access is private. I get an IllegalAccessException, when I try to invoke a method in the object returned.
5. I feel it would work, if I can somehow typecast the object returned from the method invocation to the interface class and then invoke the method.
6. The same scenario works when I don't use reflection and have them in the classpath.
Any help would be greatly appreciated. I saw a few postings related to this in the forum, but I am unable to find an answer.
Best Regards,
Ramesh.

4. Now I am unable to invoke a public method defined
in the interface, since the implementation class level
access is private. I get an IllegalAccessException,
when I try to invoke a method in the object returned.Private methods cannot be used to implement methods that the interface specifies to be public, as far as I know. A class that claimed to implement an interface that way should not compile.
5. I feel it would work, if I can somehow typecast the
object returned from the method invocation to the
interface class and then invoke the method.
6. The same scenario works when I don't use reflection
and have them in the classpath.Perhaps the class you have doesn't claim to implement the interface, but just happens to have methods with the same signature, although some of them are private? If that's the case then you have a design problem that should not be worked around this way. Fix the class to implement the interface properly and you won't have to deal with any of this nonsense.

Trying to access a private attribute of a class in the same package

Hi,
I have defined a private attribute in a class
class Sample {
     private String newString = "hello";
in another class I am trying to access newString attribute using reflection api. It is throwing hte following exception
java.lang.NoSuchFieldException: value
     at java.lang.Class.getDeclaredField(Unknown Source)
     at refletionpack.mainclass.main(mainclass.java:20)
any ideas how to do it exactly? Should stringclass.getDeclaredField("value")
have the field name(newString) as a parameter?
public class mainclass {
     static Class stringclass = Sample.class;
     static Field stringCharsField = null;
     public static void main(String args[]){
          try{
               stringCharsField = stringclass.getDeclaredField("value");
               stringCharsField.setAccessible(true);
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               System.out.println(stringChars);
          }catch(NoSuchFieldException ex){
               ex.printStackTrace();
          }catch(IllegalAccessException ex){
               ex.printStackTrace();
}

Hi,
to obtain the value of your private attribute you have to change two lines of code. At first you have to tell your class and not the field that private attributes can be accessed by using stringClass.setAccessible(true);After that you have to specify the name of the attribute to obtain which is called newString in your class which results in
stringCharsField = stringClass.getDeclaredField("newString");For the invocation of the method get(Object) you need an object first that is an instance of the analyzed class by calling Object sample = stringClass.newInstance.
Then you can retrieve the actual data of the requested field by calling String string = (String) stringCharsField.get(sample);A simpler solution would be when you make your attribute newString static. Then you can omit the necessary object for the retrieval of the attribute data and the line would result in String string = (String) stringCharsField.get(null);.
For further issues considering reflection you should read the appropriate API.
Hope it helps.

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Hello everyone,
Here is my problem. I just created a subclass of Document using the API (not XML), by creating a ClassObjectDefinition and a ClassObject. Here is the code :
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cod.setSuperclass(co);
cod.setSuperclassName(co.getName());
cod.setName("MYDocument");
ClassObject c = (ClassObject)ifsSession.createSchemaObject(cod);
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void fr.sword.ifs.GestionDocument.IFSDocument.main(java.lang.String[])
So, what am i doing wrong ?
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Guillaume
PS : i'm using Oracle iFS 1.1.9 on NT4 SP6 and Oracle 8.1.7
null

Hi Guillaume,
you're welcome. Don't know exactly, but assume that ATTRIBUTEDATATYPE_UNKNOWN
is used to check for erronous cases only
and it shouldn't be used otherwise.
Creating your own objects could be simply done via
ClassObject ifsClassObject;
DocumentDefinition ifsDocDef = new DocumentDefinition(ifsSession);
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ifsClassObject = ClassObject.getClassObjectFromLabel(ifsSession, "MYDOCUMENT");
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ifsDocDef.setClassObject(ifsClassObject);
// set attributes and content for the document...
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null

Better not to use the Reflection API?

A few companies are creating a framework for the company I work for. They use very often the Reflection API which seems strange and even "dirty programming" to me.
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Sounds more like a failing of Eclipse than of your partner companies. Reflection is part of Java. Whether an IDE should be capable of refactoring "runtime" code at compile time is another matter, however..
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Sometimes extracting a common interface will resolve these problems but not always - it's horses for courses.
Hope this helps.

Can i create more than one attributes for the custom class created using java API

Hello everyone,
I have been creating class and its attributes programatically using java APIs, I want to know that is there any way to create multipal attributs for the same class in just one call of API with all the options for each attributes,
thanks

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Hi Chao-Yi Wu ,
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Creating junit test cases using the reflection API

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Using reflection api to copy like named attributes of a class

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