Is it possible to get the declaration name of an object at runtime in java?

Question

Lets say i have a a button somewhere in the code: "JButton closeButton". I dont know that it's called "closeButton" but that's what i want to find out.

At runtime, that button gets clicked and once it does i can find out a lot about it through reflection and the AWT api - BUT what i can't do is find out where it is - how it's called in the code, what name is it declared as ("closeButton").

Is it possible to find this out from the JVM?

Is there a way to compile and run the code in such a way that the names for the instances get preserved at runtime?

Is there perhaps some type of 'javaagent' out there (free if possible) that can help me out in this situation?

Thanks

EDIT (14:23 EDT):

I am using a button as an example but it could be any type of component that can hold a value and have ActionListeners attached to it. I can obtain every bit of information via reflection about that component but i cant find it in the code. Even if there are 10 components that have been declared with the same name, that still gives me a lead, i can eliminate possibilities.

not possible without running java debugger - why do you want to do this? — Spike Gronim
– Spike Gronim, Commented Jan 31, 2011 at 19:11
The application that i am working on is massive (millions of lines), components get created and passed down various classes. Their labels are created on the fly. In this case it's actually a field whose value i need do something with, i just used a button as an example. — LoudNPossiblyWrong
– LoudNPossiblyWrong, Commented Jan 31, 2011 at 19:20

Jesus Ramos · Accepted Answer · 2011-01-31 19:26:40Z

5


import java.lang.reflect.*;

public class field1 {
      private double d;
      public static final int i = 37;
      String s = "testing";

  public static void main(String args[])
  {
     try {
        Class cls = Class.forName("field1");

        Field fieldlist[] 
          = cls.getDeclaredFields();
        for (int i 
          = 0; i < fieldlist.length; i++) {
           Field fld = fieldlist[i];
           System.out.println("name
              = " + fld.getName());
           System.out.println("decl class = " +
                       fld.getDeclaringClass());
           System.out.println("type
              = " + fld.getType());
           int mod = fld.getModifiers();
           System.out.println("modifiers = " +
                      Modifier.toString(mod));
           System.out.println("-----");
        }
      }
      catch (Throwable e) {
         System.err.println(e);
      }
   }


}

This should give you a list of all the fields of the class.

edited Jan 31, 2011 at 19:26

answered Jan 31, 2011 at 19:18

Jesus Ramos

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8 Comments

Jesus Ramos Over a year ago

sorry but the formatting got messed up and I don't have much time to fix it right now

Michael K Over a year ago

Very nice - I love reflections.

Michael K Over a year ago

Just add 4 spaces on the blank lines and that will fix it.

Jesus Ramos Over a year ago

@Michael - I do as well, I abuse them on a daily basis although this is actually the first time I've done it in Java for an actual purpose rather than just to see if I could.

LoudNPossiblyWrong Over a year ago

that's a good try but it doesnt work, i already tried that this morning. "getdeclaringClass()" returns null.

|

biziclop · Accepted Answer · 2011-01-31 19:22:15Z

3

If your "variable" is a field, then the solution using reflection (mentioned in another answer) works.

If your variable is a local variable, you can in theory use a JVMTI agent to get its name, provided that you compiled your class with debug info. And that your local variable is in scope when you check. And that nobody changed its value and there's no other variable with the same value (in which case you couldn't decide which is the one you need).

However, you should absolutely not do any of them. They are theoretical possibilities, akin to punching yourself so hard that you pass out.

answered Jan 31, 2011 at 19:22

biziclop

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Comments

pap · Accepted Answer · 2012-10-12 09:27:59Z

0

Short answer: it is not possible.

Details: What you call name has in fact nothing to do with the instance of JButton. It's just the variable that holds the referece of which allows to acces this instance at runtime. This sample code will show this mor evidently:

JButton newButton = new JButton();
JButton otherButton = newButton;

Here both variables holds a reference to teh same instance of JButton.

edited Oct 12, 2012 at 9:27

pap

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answered Jan 31, 2011 at 19:17

lweller

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3 Comments

Stan Kurilin Over a year ago

typo: newButton(); --> newButton;

LoudNPossiblyWrong Over a year ago

is there a way to map the reference to a name at runtime?

lweller Over a year ago

all AWT components have a name property, may be that is what you're looking for.

AlexR · Accepted Answer · 2011-01-31 19:17:17Z

0

I think you have 2 ways:

use java debugging API, i.e. turn your program into a small debugger.
Use byte code engineering library

answered Jan 31, 2011 at 19:17

AlexR

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