Reflect problem

I am new to Java and I am sorry if this has been raised previously.
i want to get and set all of object's fields not only public fields but also private, protected and package fields. And i have been advised that i should use one of sun.misc.unsafe or ReflectPermission, setAccessible(), ... mechanism. Is there another easier approach?
Help with source code is a kind.
Thanks in advance.

You should consider to place it in the class, for simplicity reason
Else, the only way is to write another class from outside that read/write the fields one by one with get/set methods and read/write them in a stream :
public void writeMyObject( ObjectOutputStream oos, MyClass obj) {
    oos.writeInt( obj.getMyInt() );
    oos.writeObject ( obj.getAContent() );
    //and so on ...
}If I should say something : Prefer Serialization, and prefer it as standard as possible. Custom serialization processes will require work from you. Each time you change your class, each time you add, remove or modify a field, you'll have to modify your process...

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Reflection problems with null pointer exception

I am having a problem with reflection. I keep getting a NullPointerException and can't figure out why.
It is happening when I call this:
ResponseObject result = (ResponseObject)method.invoke(classInstance, argArray);
I can't figure out what the problem is. I had this reflection working, and then I made some changes to how the argument array was created. In the end, the argarray is the same.
Any ideas?

Also, the API for the method class says that a
NullPointerException is thrown if the object in the
first argument is null. I have tested for this, and
it is not null.does it? read again, because giving 'null' as the first argument is perfectly legal. how else would you reflectively invoke a static method, since you might not have an actual instance of the class to pass

Reflection problem: Creating Objects

The Reflection Tutorial mentions this line "Fortunately, with the reflection API you can create an object whose class is unknown until runtime" but the examples given are hardcoding the classnames!!!
Here is the example given
class SampleNoArg {
public static void main(String[] args) {
Rectangle r = (Rectangle) createObject("java.awt.Rectangle");
System.out.println(r.toString());
static Object createObject(String className) {
Object object = null;
try {
Class classDefinition = Class.forName(className);
object = classDefinition.newInstance();
} catch (InstantiationException e) {
System.out.println(e);
} catch (IllegalAccessException e) {
System.out.println(e);
} catch (ClassNotFoundException e) {
System.out.println(e);
return object;
now how do i create a object at runtime without 'really' knowing what its class is. The following will definitely not work and am providing it as additional help in making others understand my problem.
String cName = c.getName(); // fully-qualified name
Object o = c.newInstance();
if ( ( (cName)o).compareTo(...) ) {...}
// where it is assumed that c is a Class i got previously, and that the class implements the Comparable interface.
So anybody has any idea on how to do this? Thanks in advance.

If you're talking specifically about comparing Objects that may or may not implement comparable, I suggest you create your own Comparator implementation that will work with any of the objects you are expecting to create.
If you are talking about executing methods on general objects, there are two cases:
1. Your object implements a known interface. In this case, you can check for this, using instanceof, and cast the object in order to call the required method.
2. Your object should have a known method. In this case, use Class.getDeclaredMethod to retrieve a Method instance, and then execute that.
RObin

Reflection problem - NoSuchMethodException

Dear all,
I am trying to use java reflection based on an article http://developer.java.sun.com/developer/qow/archive/86/ with non-default constructor example
I have a method I'd like to call on runtime :
loadProjects(String[] fields, String sWhereClause, String sOrderBy) throws ServerException, ...
Without reflection I do the following :
//without reflection
GlobalObjectManager gom = session.getGlobalObjectManager();
gom.loadProjects(new String[] { "ObjectId", "Name"},null,null);
With reflection I tried the following :
//with reflection
GlobalObjectManager gom = session.getGlobalObjectManager();
String objectName = "Projects"; //could be "Resources", "Others", ...
String methodName = "load" + objectName;
Class[] constructorArgumentTypes = { String[].class, String.class, String.class };
Constructor classConstructor = gom.getClass().getConstructor(constructorArgumentTypes);
Method classMethod = gom.getClass().getMethod(methodName, null);
Object[] constructorArgs = { new String[] { "ObjectId", "Name" }, null, null };
Object dynamicObject = classConstructor.newInstance(constructorArgs);
classMethod.invoke(dynamicObject, null);
I get the NoSuchMethodException error :
java.lang.NoSuchMethodException: com.primavera.integration.client.GlobalObjectManager.<init>([Ljava.lang.String;, java.lang.String, java.lang.String)
     at java.lang.Class.getConstructor0(Class.java:1769)
     at java.lang.Class.getConstructor(Class.java:1002)
     at net.primafrance.reflect.InstantiateRuntimeClass.main(InstantiateRuntimeClass.java:50)
Any comment will be appreciated.


Dear all,
I am trying to use java reflection based on an article
http://developer.java.sun.com/developer/qow/archive/86/
with non-default constructor example
I have a method I'd like to call on runtime :
loadProjects(String[] fields, String sWhereClause,
String sOrderBy) throws ServerException, ...
Without reflection I do the following :
//without reflection
GlobalObjectManager gom =
session.getGlobalObjectManager();
gom.loadProjects(new String[] { "ObjectId",
"Name"},null,null);
With reflection I tried the following :
//with reflection
GlobalObjectManager gom =
session.getGlobalObjectManager();
String objectName = "Projects"; //could be
"Resources", "Others", ...
String methodName = "load" + objectName;
Class[] constructorArgumentTypes = { String[].class,
String.class, String.class };
Constructor classConstructor =
gom.getClass().getConstructor(constructorArgumentTypes)
Method classMethod =
gom.getClass().getMethod(methodName, null);
Object[] constructorArgs = { new String[] {
"ObjectId", "Name" }, null, null };
Object dynamicObject =
classConstructor.newInstance(constructorArgs);
classMethod.invoke(dynamicObject, null);
I get the NoSuchMethodException error :
java.lang.NoSuchMethodException:
com.primavera.integration.client.GlobalObjectManager.<i
it>([Ljava.lang.String;, java.lang.String,
java.lang.String)
     at java.lang.Class.getConstructor0(Class.java:1769)
     at java.lang.Class.getConstructor(Class.java:1002)
at
net.primafrance.reflect.InstantiateRuntimeClass.main(I
stantiateRuntimeClass.java:50)
Any comment will be appreciated.
Your problem here is that you are constructing your object via reflection, which is not necessary.Look at what you are doing in your non-reflection code...From the session, get the GlobalObjectManager. Then call loadProjects( String[ sa, String s1, String s2) on that object.All you need to do in your reflection is replace the explicit call to loadProjects with the reflection equivalent...
GlobalObjectManager gom = session.getGlobalObjectManager();
//** Now we do the reflection
Class gomClass = gom.getClass();
Class[] paramTypes = { String[].class, String.class, String.class };
Object paramValues = { { new String[] { "ObjectId", "Name" }, null, null };
Method loadProjectsMethod = gomClass.getMethod( "loadProjects", paramTypes );
loadProjectsMethod.invoke( gom, paramValues );What you were doing wrong was you were retrieving the gom as before but then trying to construct another one using the parameters expected for the loadProjects method.

Enumset reflection problem

Hi All,
I faced with a problem over a week and I hope somone has a solution for that.
I have enum like this:
package com.lo.enums;
public enum Tag{
Tag1,
Tag2,
Tag3
I have tried to create dynamically using reflection EnumSet of that enum but getting always java.lang.ClassNotFoundException exception.
I have tried to do like this:
String type = "java.util.EnumSet<com.lo.enums.Tag>";
Class clazz = Class.forName(type);
Thanks for the help.

There is no class named "java.util.EnumSet<com.lo.enums.Tag>". You cannot reflectively create parameterized classes. Furthermore, EnumSet is an abstract class, providing static factories to create Sets on Enums. So you may get the EnumSet class and one of the needed static methods by reflection and invoke it passing the according enum class.

Reflection problem with private class

I am trying to write a junit on private class and I am stuck not knowing how to access private class.
Here is the structure of my code:
public abstract class cars extends auto{
private class model{
String name;
String year;
String make;
private model getInfo(name, year, make{
Model mod = new Model();
mod.name = "Echo";
mod.year = "1992";
mod.make = "Toyota";
return mod;
}Basically how do I use reflection so I can write assert such as
assertEquals(getInfo.year, "1992");Thanks in advance!

You don't. Private methods, members, and classes are considered implementation details and should not be directly tested with your unit tests.

Reflection problem: can not access a member of class java.lang.IllegalAcces

package org.struts.ets.utility;
import java.lang.reflect.Constructor;
import java.lang.reflect.Field;
import java.lang.reflect.InvocationTargetException;
import java.util.ArrayList;
import java.util.Iterator;
import java.util.List;
import org.struts.bean.FieldTrouble;
import org.struts.bean.GenericDAOBean;
public class DynamicObjectCreation
     public static void main(String... args)
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          try
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               //Class<?> c = FieldTrouble.class;
               /*Class<?> c = null;
               try
                    c = Class.forName("org.struts.bean.FieldTrouble");
               } catch (ClassNotFoundException e)
                    e.printStackTrace();
               Field f = c.getDeclaredField("var1");
               //f.setInt(ft, 42); // IllegalArgumentException
               f.set(ft, new String("A"));
               System.out.println(ft.getVar1());
               // production code should handle these exceptions more gracefully
          } catch (NoSuchFieldException x)
               x.printStackTrace();
          } catch (IllegalAccessException x)
               x.printStackTrace();
}// If I put FieldTrouble.java in any other package than the current package I am running this code from. I get the following error:
java.lang.IllegalAccessException: Class org.struts.ets.utility.DynamicObjectCreation can not access a member of class org.struts.bean.FieldTrouble with modifiers ""
     at sun.reflect.Reflection.ensureMemberAccess(Unknown Source)
     at java.lang.reflect.Field.doSecurityCheck(Unknown Source)
     at java.lang.reflect.Field.getFieldAccessor(Unknown Source)
     at java.lang.reflect.Field.set(Unknown Source)
     at org.struts.ets.utility.DynamicObjectCreation.main(DynamicObjectCreation.java:35)
I tried all possible ways of creating class as:
Class<?> c = ft.getClass(); OR
Class<?> c = FieldTrouble.class; OR
               /*Class<?> c = null;
               try
                    c = Class.forName("org.struts.bean.FieldTrouble");
               } catch (ClassNotFoundException e)
                    e.printStackTrace();
Edited by: ..-__Kris__-.. on Feb 21, 2008 10:26 AM
Edited by: ..-__Kris__-.. on Feb 21, 2008 10:26 AM

Any hidden performance or memory issue here?
Let us consider an object:
public class SomeObject
     private String fieldA;
     private String fieldB;
     private String fieldC;
     private String fieldD;
     private String fieldE;
     //... say 50 declared fields....
     public SomeObject()
     public SomeObject(String fieldA, String fieldB)
          this.fieldA = fieldA;
          this.fieldB = fieldB;
// getters and setters..
}When I create an object using the constructor with only two fields initialized such as the following code above, and look at what is happening to other fields as shown in the code below, I see that they are also AVAILABLE, now this is important, but they are set to null. What I wanted to know was, if I created an object with many fields, as many as 50 (getDeclaredFields = 50), and used a constructor with only two input fields to initialize an object, I still have 48 other fields available but set as NULL's. When I create more than 100,000 of these objects in a list and send to a .jsp page, I am unable to understand if this has more memory load than when you use a list of another object which has actually has only two declared fields in it. Each of this new object will have only two declared fields, when I say getDeclaredFields() it would return 2.
This is where I am unable to figure out if this has anything to do with performance or memory, rather, what is the difference between the many possible ways you can initialize an object when there are too many fields which you probably won't use? Either create a new constructor with only two input arguments OR a generic constructor with all fields as input arguments but all those fields which you won't use assigned NULL's OR create another new object with only two declared fields
SomeObject someObj = new SomeObject("abcd","cdef");
          Field[] fields = someObj.getClass().getDeclaredFields();
          System.out.println("Number of available fields: " + fields.length);
          for(int i = 0 ; i < fields.length ; i++)
               try
                    fields.setAccessible(true);
                    System.out.println("Field " + i + ", with value: " + fields[i].get(someObj));
                    fields[i].get(someObj);
               } catch (IllegalArgumentException e)
                    e.printStackTrace();
               } catch (IllegalAccessException e)
                    e.printStackTrace();
          }Edited by: ..-__Kris__-.. on Mar 23, 2008 5:04 PM
Edited by: ..-__Kris__-.. on Mar 23, 2008 5:05 PM

Reflection problem

Hi there,
hi there I'm trying to invoke a method using reflection, however, the arguments of the methods could either be a primitive datatype like int.class or else a regular Class like String.class
However, the indication as to which is not known till runtime
Basically it looks like this.
//Setting up the target class
Class MyClass = Class.forName("MyDeadlyClass");
String paramDatatype=getParamType(); //returns a String, could be equal to "String.class" or "boolean.class"
Class parameterClass = Class.forName(paramDatatype);
Class [] classes = new Class[]{classtype};
MyMethod mthd = MyDeadlyClass.getMethod("overloadedMethod",new Class[]{paramDatatype});
Now obviously this doesn't work as 'Class.forName(paramDatatype)' returns a ClassNotFoundExceptoin for any of the primitive.class e.g. int.class or boolean.class as they're indeed primitives and not datatypes.. But I can't create an array of Class with the likes of int.class unless I hard code it in that the array is going to contain int.class
i.e.
Class[] classes = new Class[]{int.class};
will create an array of classes with the int.class as the first entry. That's fine. What do I do when I only have that info at runtime.
Does anyone know of a way around this?
Thanks,
Mark.

Try having some static methods that will return primitive type classes, i.e.
public class MyClassHelper
   static public Class getIntClass () { return int.class; }
   static public Class getBooleanClass () { return boolean.class; }
   // And so on...
}Then have a "build" method that will take the param names at runtime and call the methods to build up the array of classes...i.e.
static public Class[] classTypeArrayBuilder (String[] classnames)
    Class classes[] = new Class[classnames.length];
     for (int i = 0; i < classnames.length; i++)
          Class c = null;
          if (classnames.equals (int.class.getName ()))
c = MyClassHelper.getIntClass ();
// And so on...
classes[i] = c;
return classes;
It's messy but should work...

Reflection Problem (should be easy)

Hi,
I have a method of a class that I would like to invoke at runtime using the Reflection API. I know both the class name and method name as well as the parameters that the method accepts at compile time.
The class name is: TestMethod
The method name is: e(String t, int k); //this needs to be invoked
I am confused on how to code this using the Reflection API. Please can someone provide me with the shortest amount of code for me to do this.
This needs to be done in Reflection not any other way!
Thanks
Rizwan

The class name is: TestMethod
The method name is: e(String t, int k); //this needs
to be invoked
I am confused on how to code this using the Reflection
API. Please can someone provide me with the shortest
amount of code for me to do this.This seems awfully lot like homework... well, whatever..
Class.forName("TestMethod").getMethod("e",new Class[]{String.class,Integer.TYPE}).invoke(o,a);I don't believe there is a shorter version without replacing the string literals with 1-char variables.
- Marcus

Another reflection problem

Hi All,
Can someone give me an example of how using reflection to initiate this:
ArrayList<Integer>.
Thanks

You cannot. It's of no use anyway, as by now generics are erased at runtime.

Lights reflecting in glasses.

Hi there. Is there any way of getting rid of flood lights reflecting off of someone's glasses? I have interviewed someone who wears glasses and now that I can't redo the interview, I'm faced with trying to come up with an answer to this reflection problem. Is there any kind of "photo shop" button in iMovie or something I can use in iMovie that can help minimize flood light glare on glasses?
Thanks for any help.

Hi
No - that's why one must be very observant when recording. And during recording one can use a polariod filter on the lens to minimise this effect but to be repaired in after hand is only for pro's with FinalCut Pro and Motion and other elaborative tools - still far far from easy to deal with.
To fix glases one need a PhotoShop like tool and key-framing each frame for movements so that the correcting filter follow exactly - else it will be very disturbing - much more than the reflexes in first hand.
Most common way to minimiseing this problem is to
• use cut-aways - replace picture with any other relevant to the story while keeping audio continuing.
Yours Bengt W

Reflection leading to JVM crash?

I've got an interesting problem where it appears that use of reflection code is leading to a complete JVM crash. The top of the stack trace in the hs_err_pid log is:
C 0x00031000
j sun.reflect.GeneratedMethodAccessor146.invoke(Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;+40
j sun.reflect.DelegatingMethodAccessorImpl.invoke(Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;+6
j java.lang.reflect.Method.invoke(Ljava/lang/Object;[Ljava/lang/Object;)Ljava/lang/Object;+111
j org.infohazard.domify.ElementAdapter$MethodNodeListAdapter.item(I)Lorg/w3c/dom/Node;+55
j org.infohazard.domify.NodeAdapter.getNextSibling()Lorg/w3c/dom/Node;+48The virtual machine was started with -Xint, so theoretically everything on the stack should have been interpretted Java code. The problem seems to surface regardless of garbage collection algorithm, heap size, LD_ASSUME_KERNEL level, etc. I've edited virtually every JVM parameter I can think of and it always comes back. We're running on a RedHat Enterprise 3, dual Xeon processor box if anybody suspects this is connected to the underlying platform.
More specific for the platform:
OS:Red Hat Enterprise Linux ES release 3 (Taroon Update 3)
uname:Linux 2.4.21-20.ELsmp #1 SMP Wed Aug 18 20:46:40 EDT 2004 i686
libc:glibc 2.3.2 NPTL 0.60
rlimit: STACK 10240k, CORE 0k, NPROC 7168, NOFILE 65535, AS infinity
load average:13.48 12.83 12.68
CPU:total 4 family 15, cmov, cx8, fxsr, mmx, sse, sse2, ht
Memory: 4k page, physical 941k(228k free), swap 511k(509k free)
vm_info: Java HotSpot(TM) Server VM (1.5.0_07-b03) for linux-x86, built on May 3 2006 00:32:58 by java_re with gcc 3.2.1-7a (J2SE release)
Message was edited by:
cchandler

Extensive load testing seems to have solved the problem. Our application accepts uploads and was using the Jakarta Commons file-upload utility version 1.0. Apparently when files are uploaded and they are stored on disk it immediately called deleteOnExit() on the File object. This triggers a known
problem in the JVM:
http://issues.apache.org/jira/browse/FILEUPLOAD-95
http://bugs.sun.com/bugdatabase/view_bug.do?bug_id=4513817
After updating our jars and testing it the reflection problems have gone away. I can only assume the original problem is an interaction between the file handles the JVM has to track, a very long running application, and the linux kernel as the RSS approaches the linux 2GB boundary.

Help me with reflection

Hi forum,
This reflection problem is giving me trouble.Please any one give me your suggestions.
In my little project, i am passing the method name as string to a radiobutton actionPerformed class.Inside this actionPerformed class i need the parameterTypes of the method.
I understand that only methodType.getParameterTypes is possible.
1. is there a way to typecast the string name of the method to Method type to get the parameter types?
2. Or can i pass the method as any other type rather than String to avoid this problem?
Thank you all.

1. is there a way to typecast the string name of the
method to Method type to get the parameter types?You should look up "casting" again.
2. Or can i pass the method as any other type rather
than String to avoid this problem?Look at this thread for ideas about how to do it a better way:
http://forum.java.sun.com/thread.jspa?threadID=758173

Java Reflection: Trying to access a constrcutor with an array argument.

Having some reflection problem... upon reflection maybe I shouldn't use reflection... :-)
The classes I use to test this are defined as follows:
class MyTestClass{
public long[] _array;
public MyTestClass(long[] array)
    _array = array;
class MyTestClass2{
public int[] _array;
public MyTestClass2(int[] array)
    _array = array;
class MyTestClass3{
public String[] _array;
public MyTestClass3(String[] array)
    _array = array;
class MyTestClass4{
public Long[] _array;
public MyTestClass(Long[] array)
    _array = array;
}and this is how I try to access it:
// Only classes that have a constrcutor with a single
// param which is an array can be used with this method.
// The class also has to define a public field called "_array"
// which is of the ssame type as the parameter of the
// constructor
public Object getNewInstanceOf(String className)
    // getValues uses reflection to instanciate an array of objects of
    // certain types which are not known to start with, i.e getValues
    // can return Long[] or Integer[] or String[]
    Object[] values = getValues();
    Class myClass = Class.forName(className);
    myClass..getField("_array");
    Class paraClass = field.getType();
     Constructor constructor = myClass
                .getConstructor(new Class[]{paraClass});
    // the problem occurs here, I think I would have to cast "values" to the
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    Object myInstance = constructor.newInstance(new Object[]{values});
   return myInstance;
private Object[] getValues()
    // use reflection to create the array
}and this is the error I get
java.lang.IllegalArgumentException: argument type mismatch

we can be much helpfull if we do not know which line excatly throws exception
normaly stack trace shows the line number so can you re-post your code highlitine the line which throws given exception

3M Anti-Reflective Film Solution For New Macbooks

I'm eagerly awaiting my new Macbook, and I thought I'd be industrious and search for a good solution for their glass reflection problems. I hope the site moderator doesn't mind me posting the following links.
This easy-clean matte film should fit on both 13" and 15" Macbooks.
_ARM200 PDF Brochure:_ http://multimedia.3m.com/mws/mediawebserver?66666UuZjcFSLXTt48T_OxTcEVuQEcuZgVs6 EVs6E666666--
ARM200Website:http://solutions.3m.com/wps/portal/3M/enUS/Vikuiti1/BrandProducts/main/productliterature/productinformation/PC_7_RJH9U52 30GE3E02LECFTDQ8KB7nid=R0ZHLXBJXGbe0H01CMQK62gl
Message was edited by: KL3V3R HANS

I have a nushield. It works really great and it is sized just right for the Macbook screen. There are two versions. It doesn't effect the quality of picture. It does reduce glare and it protects your screen from being scratched. Go to www.nushield.com. It's worth the money. Plus it supports a small American company. I also like Zagg shields (lifetime warranty). Zagg shields protect the macbook from scratches. It's a film you put on. It doesn't add weight and it doesn't heat up your Macbook like some plastic cases would. Check out nushield!

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