Method.invoke hangs. HELP

that is:
Method.invoke(obj,args)
It works just fine the first dozen or 2 times, same obj, same args. No prob.
Then it hangs.
No exception message. nothing. It just stops at invoke. And the Task Manager says the thread is eating 99% of the CPU, so it's spinning away in some loop I guess. The method getting invoked DOES NOT get called. It's definitely hanging inside invoke somewhere. Is this a bug?

one more clue: There're 100-200 threads calling Method.invoke when the hang happens. The hang is permanent as far as I can tell. I've tried using synchronize in various ways. No luck.

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Method.invoke hangs?

I'm trying to send a Class over a network, then invoke a Method inside the class.
                        final Method command = clazz.getDeclaredMethod("exec");
                        try {
                            System.out.println("Invoked0");
                            command.invoke(null);
                            System.out.println("Invoked1");
                        } catch (Exception e) {
                            throw new RuntimeException(e);
                        }Only Invoked0 prints, and there is no Exception. Whats wrong?
    class CommandClassLoader extends ClassLoader {
        public Class<?> defineClass0(String name, byte[] b, int off, int len) {
            return defineClass(name, b, off, len);
    }

Oops, didn't realize I was throwing there, its printing a NPE.
java.lang.NullPointerException
        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:597)
        at colby.client.Client$1$2.run(Client.java:63)
        at java.util.concurrent.Executors$RunnableAdapter.call(Executors.java:441)
        at java.util.concurrent.FutureTask$Sync.innerRun(FutureTask.java:303)
        at java.util.concurrent.FutureTask.run(FutureTask.java:138)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.access$301(ScheduledThreadPoolExecutor.java:98)
        at java.util.concurrent.ScheduledThreadPoolExecutor$ScheduledFutureTask.run(ScheduledThreadPoolExecutor.java:207)
        at java.util.concurrent.ThreadPoolExecutor$Worker.runTask(ThreadPoolExecutor.java:886)
        at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:908)
        at java.lang.Thread.run(Thread.java:619)That doesn't really make sense though? Why would it be happening there?

How to trap null return values from getters when using Method.invoke()?

Hi,
I am using Method.invoke() to access getters in an Object. I need to know which getters return a value and which return null. However, irrespective of the actual return value, I am always getting non-null return value when using Method.invoke().
Unfortunately, the API documentation of Method.invoke() does not specify how it treats null return values.
Can someone help?
Thanks

What do you get as a result?I think I know what the problem is.
I tested this using following and it worked fine:
public class TestMethodInvoke {
public String getName() {
return null;
public static void main(String args[]) throws SecurityException, NoSuchMethodException, IllegalArgumentException, IllegalAccessException, InvocationTargetException {
Object o = new TestMethodInvoke();
Class cls = o.getClass();
Method m = cls.getMethod("getName", (Class[]) null);
Object result = m.invoke(o, (Object[])null);
if (result == null) {
System.err.println("OK: Return value was null as expected");
else {
System.err.println("FAILED: Return value was NOT null as expected");
However, when I use the same technique with an EJB 3.0 Entity class, the null return value is not returned. Instead, I get a String() object. Clearly, the problem is the the EJB 3.0 implementation (Glassfish/Toplink) which is manipulating the getters.
Regards
Dibyendu

Dynamic casting of Method.invoke() return

Can anyone clue me in on how to cast the return of Method.invoke() based on Method.getReturnType() or whatever else might work dynamically....that is without knowing which method until runtime?
Thanks,
Brad

Thanks for helping me get a grip....makes perfect sense, I guess I was just wondering how far you could take the runtime decisions thing.
Can I say that, ( and it seems obvious but... ), programatic flexibility and runtime decision making can only be taken so far - and has to be made in the context of certain presumptions at compike time.
I can see that in implementing the:
<jsp: setParameter name="myBean" property="*" />
Presumptions are made that the values passed to
the bean setter methods will be String objects and that the
values returned from the:getter methods using:
<jsp: getProperty name="myBean" property="whaterver" />
will also be String objects.
Reality check?
Thanks again,
Brad

Method.invoke

Hi,
I'm trying to dynamically load various classes at runtime but have encountered a problem with the Method.invoke() method.
Class c = Class.forName( "car" );
Method m = c.getDeclaredMethod("Execute", new Class [] { String.class } );
object res = m.invoke( Object obj, Object[] arg); // here is the problemI do not know what parameters to set inside Method.invoke(). Looking for some advice here. All the classes that I want to load implement an interface;
interface loadplugin
boolean Execute(String str);
}Any suggestions?

Hi,
You put the parameters the Method needs to the Object [] -
This is a call you know:
loadplugin myLoadPlugin = new LoadpluginImplementingClass();
boolean result = myLoadplugin.Execute("Hallo World");The corrsponding call to the Method object is:
Boolean result = (Boolean)m.invoke(myLoadpugin, new Object[]{"Hallo World"}); The Method object only can hanlde Object types. For any standard data type (int, boolean, double, etc.) the corresponding Wrappers have to be used. So the return in case of the Method-Object call is Boolean, not boolean.
I hope this helps,
Lars.

Using java.lang.reflect.Method.invoke on a static method?

This is probably a FAQ, but I am finding it impossible to construct a search which answers this question for me.
How do I call java.lang.reflect.Method.invoke on a static (e.g. class) method? Is it even possible?
Thanks,
dwh

Is this of any help?
http://www.esus.com/javaindex/j2se/jdk1.2/javalang/reflection/reflection.html
Cheers,
Joris

Reflections invoke NoSuchMethodException help

Hello everyone,
I've been reading a lot about reflections on the forum lately, and figured it was the perfect way to dynamically call a method based on string input. However, while I can get the SampleInvoke program that is in the reflections tutorial to work, I can't seem to invoke a method that I write myself. I think I'm close, but there must just be a little something wrong...could anyone lend me a hand?
   public void foo()
        System.out.println("Worked!");
   } // end foo
   public void bar()
        Class c = this.getClass();
        Class[] params = new Class[] { null };
        Object[] args = new Object[] { null };
        Method m;
           try {
               m = c.getMethod("foo", params);
              m.invoke(c, args);
             } catch (NoSuchMethodException e) {
                 System.out.println(e);
             } catch (IllegalAccessException e) {
                 System.out.println(e);
             } catch (InvocationTargetException e) {
                 System.out.println(e);
   }What I'm getting is:
java.lang.NoSuchMethodException: SampleInvoke.foo(null)
But it's clearly in the class...
Any help is appreciated,
Joe

enlightenment
Try
m = c.getMethod("foo", null);
Oh! Okay, if I do that on both the c.getMethod line
AND the m.invoke line, it works, however, both show
up as warnings, "Varargs arguments null should be
cast to Class[] when passed to the method
getMethod..."
or
"Varargs arguments null should be cast to Object[]
when passed to the method invoke..."
However, when I attempt to cast them, it goes back to
NoSuchMethodException output. I guess I'm willing to
live with a bunch of warnings, but I wonder why?Try to feed them "new Class[0]" and "new Object[0]". Haven't dealt with varargs yet, so I can't help you with that.

Refer to a JTabbedPane from the porgram /&what is the first method invoked?

Hi there,
I have been researching for this for a while and couldn?t find the answer, maybe some of you guys can help.
Situation: I have a program with some JTabbedPane in it
          panel.setLayout(new BorderLayout());
          JTabbedPane pane = new JTabbedPane();
          pane.setTabPlacement(JTabbedPane.LEFT);
          pane.setFont(new Font("Times New Roman", Font.PLAIN, 16));
          pane.add("User", userPanel);
          pane.add("Group Type", groupPanel);
          pane.add("Agent", agentPanel);
          panel.add(pane, BorderLayout.CENTER);
Question1: sometimes, when the user clicks on JButton, I want to refer him directly to a different ?JTabbedPane?. Meaning, I don?t want him to physically press the ?JTabbedPane? to get there, but I want the program to take him directly to the relevant section. how to do that?
Quesiotn2: what is the first method invoked when referred to a JTabbedPane. Or, how can I count how many times the users has referred to a particular section.
Thanks for any help :-)
dgz

panel.setLayout(new BorderLayout());
JTabbedPane pane = new JTabbedPane();
pane.setTabPlacement(JTabbedPane.LEFT);
pane.setFont(new Font("Times New Roman", Font.PLAIN,
16));
pane.add("User", userPanel);
pane.add("Group Type", groupPanel);
pane.add("Agent", agentPanel);
panel.add(pane, BorderLayout.CENTER);
Question1: sometimes, when the user clicks on JButton,
I want to refer him directly to a different
?JTabbedPane?. Meaning, I don?t want him to physically
press the ?JTabbedPane? to get there, but I want the
program to take him directly to the relevant section.
how to do that?
Try this tabPane.setSelectedIndex(anIndex) //eg a number between 0 and tabPane.getTabCount
Quesiotn2: what is the first method invoked when
referred to a JTabbedPane. Or, how can I count how
many times the users has referred to a particular
section.You can get the component at an index, check if it is showing and update a count variable eg
Vector counter = new Vector();
public void checkVisibleTab() {
for(int x = 0; x < tabPane.getTabCount(); x++) {
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} You can then iterate through the vector and find how many times a particular number appears and use it for your specific purpose.
ICE

Java.lang.NoSuchMethodException Using Method.invoke(...)

I try to use Method.invoke() to invoke a method from a class. The method
has parameters with type JTextArea and JMyFrame, but I got the error
messages java.lang.NoSuchMethodException . Any ideas???
If I remove parameter "JFrame mainFrame" in start() method and it is working fine. Not sure why JMyFrame will throw this exception, as JMyFrame is derived from JFrame class
public class MyFrame extends JFrame
     try
ClassLoader loader
= new MyClassLoader(Integer.parseInt("3"));
Class c = loader.loadClass("NewMenuPackage.NewMenu");
Class[] params = { JTextArea.class, JMyFrame.class };
     Method m = c.getMethod("start", params);
     Object obj = c.newInstance();
m.invoke(obj,
     new Object[] {
          textArea,
          JMyFrame.this
catch (Throwable e)
JOptionPane.showMessageDialog(this, e);
package NewMenuPackage;
import javax.swing.*;
public class NewMenu
     private static JMenuItem menuItem = new JMenuItem("New Menu");
     public static JMenuItem getJMenuItem()
          return menuItem;
     public static void start(JTextArea textArea, JFrame mainFrame)
          System.out.println("NewMenu->start()...");
}

Your "params" Class array has to specify the exact classes of the method, not subclasses. The line that is causing the NoSuchObjectException to be thrown is "c.getMethod("start", params);".
You have to write your own reflection utility methods to find a method that matches on parameter subclasses.

Using Reflection - Method.invoke()

Hi all,
Facing a problem in using the Reflection API. Can anyone tell me how to use the invoke, which is available with Method. Problem statement. - I want to create a method. And then invoke that method using method1. invoke. But this can take only the following arguments - (Object, Object [ ] ). I cant figure out why I need to pass on an object ? and an array of objects ?

If you read the docs for Method.invoke, you'll see that the first argument is the object on which you wish to invoke the method, and the second argument is the parameters (with primitives wrapped appropriately).
foo.bar("abc", 123);
// becomes
meth.invoke(foo, new Object[] {"abc", new Integer(123) }); (if I haven't screwed up the syntax of the array initialization)
http://java.sun.com/docs/books/tutorial/reflect/

Is Method.invoke (Object,Class[]) efficient

hi
How efficient is the method invoke compared to explicit method calling?
thanks

I cna't give any solid numbers either, but when I've used it I've noticed it to be much slower than directly invoking the method. Ballpark I'd guess 5 times as much overhead, but don't hold me to that. Of course, if the work your method does is large compared to method invocation overhead, then it shouldn't really matter.

Method.invoke() thread save ?

Hi to you all,
Is the method invoke on the Object Method in the java.lang.reflect package threadsafe ?
Greetz-tbone

I'have created a with a college a ReflectionMap where getter and setter maps to the javabean properties
using reflection at creation time the map cache the methods of the underlaying object
now we want to use it i a multiple thread context
where more than one thread can access the map a time
if the implementation of Method is threadsafe then we do not need synchronisation else
we must synchronize our map.
and sinds that synchronisation is a performence bottleneck i would like to live it out.
Tbone

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BR
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Hi check my weblog: https://wiki.sdn.sap.com/wiki/x/du0

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Method.invoke hangs. HELP

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