Return objectname in java

Question

Now i wanna write a method like this:

public String getObjName(Object obj)

This method return the name of this object,for example,

Student stu = new Student();
String objname = getObjName(stu);

Then objname will be "stu".

I learn a lot about java reflection,but i still confused with this issue,every tips will help.

Why do you want that? This might be possible with reflection, but certainly it would be too complex to be worth. Alternative is to use a `Map` to store mapping from object name to object, or object to object name. But you should be clear that you really need this. — Rohit Jain, Sep 25 '13 at 08:00
possible duplicate of [Java Reflection: How to get the name of a variable?](http://stackoverflow.com/questions/744226/java-reflection-how-to-get-the-name-of-a-variable) — Ilya, Sep 25 '13 at 08:01
Unclear to me, as to what the requirement is :( Though If I understood this a bit slightly, then I guess you are looking to `return` the name of the object. You can have a variable in the class, that will hold this name for each object (like String objName which will be set everytime you create an object like `Student stud1 = new Student("stud1")), and now override `toString()` method from `Object` class, which will return this `objName` variable of the class. — nIcE cOw, Sep 25 '13 at 08:08

Sergey Morozov · Answer 1 · 2013-09-25T08:10:21.870

1

You can't obtain variable name using reflection. You can obtain only class name:

stu.getClass().getName();

edited Sep 25 '13 at 08:10

answered Sep 25 '13 at 08:02

Sergey Morozov

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1

How is this answering the question? It's like someone asking you for *Apple*, and you give him *Hammer*, saying you don't have apple. – Rohit Jain Sep 25 '13 at 08:03
He is asking for the name of the object he kept for that class..... basically name of the object passed as value to the function. – AurA Sep 25 '13 at 08:06
I write that it is impossible. – Sergey Morozov Sep 25 '13 at 08:06
I also think the same.... you can get the name of class it is instance of but getting the name of object he kept is not possible. – AurA Sep 25 '13 at 08:07

Ilya · Answer 2 · 2013-09-25T08:18:20.350

You can use this class:

public final class NamesCollector 
{
   final static Map<String, Object> ALL_NAMES = new WeakHashMap<String, Object>();

   private NamesCollector(){}

   public static <T> T createObject(Class<T> clazz, String name) 
   {
      final T retVal;
      try
      {
         retVal = clazz.newInstance();
      }
      catch (final Exception ex)
      {
         throw new RuntimeException(ex);
      }
      ALL_NAMES.put(name, retVal);
      return retVal;
   }

   public static String getObjName(Object obj)   
   {
      for (Entry<String, Object> entry : ALL_NAMES.entrySet()) 
      {
         if (entry.getValue().equals(obj)) 
         {
             return entry.getKey();
         }
      }
      return null;
   }
}

Usage:

Student stu =  NamesCollector.createObject(Student.class, "stu");
String name = NamesCollector.getObjName(stu);

score 1 · Answer 3 · answered Sep 25 '13 at 08:06

You cannot access the name of a local variable at runtime. Apart from that its rather useless as the following example shows:

Student stu = new Student();
Student stu2 = stu;

getObjName(stu); // should return "stu"
getObjName(stu2); // should return "stu2"

Two different 'object names' for the same object? Better use .toString()!

score 1 · Accepted Answer · answered Sep 25 '13 at 08:06

First of all I think this is impossible. Reason for that is that you won't get name of object but of a reference to it. Look at example:

    Student stu = new Student();
    Student stu2 = stu;
    String objname = getObjName(stu);

Which name you think It'll write? You can get name of the class of the instance, but name of the instance reference variable, I don't think so.

Additionally variable reference representation is not always the same in bytecode as you see it in your code.

Return objectname in java

4 Answers4