Java - determine where an object is instantiated from object's class

Question

Say I have a class called MyClass, within this class, I want to find out the class name that instantiated an object of MyClass, for example:

class MyClass {
    final String whoCreatedMe;
    public MyClass() {
        whoCreatedMe = ???
    }
}

public class Driver {
    public static void main(String[] args) {
        System.out.println(new MyClass().whoCreatedMe); // should print Driver
    }
}

Strings are immutable - there simply isn't any method that would enable you to change a String (unless you use Reflection - and go to hell). — Jordi Castilla, Jul 02 '15 at 07:25
Lets step back: why do you think you want to do that? What is the problem that you actually want to solve? — GhostCat, Jul 02 '15 at 07:47

score 3 · Answer 1 · answered Jul 02 '15 at 07:37

This is not advisable, and probably breaks in the most unexpected (and expected) ways. So I hope you're not going to use this in production code.

public class Temp {

    static class TestClass {
        public final String whoCreatedMe;
        public TestClass() {
            StackTraceElement ste = Thread.getAllStackTraces().get(Thread.currentThread())[3];
            whoCreatedMe = ste.getClassName();
        }
    }

    public static void main(String[] args) throws Exception {

        System.out.println(new TestClass().whoCreatedMe);
    }
}

score 2 · Answer 2 · edited Jul 02 '15 at 07:25

2

pass Caller class name in constructor..

class MyClass {
    String whoCreatedMe;
    public MyClass() {
    }
    public MyClass(String mCallerClass) {
        this.whoCreatedMe = mCallerClass;
        System.out.println(this.whoCreatedMe+" instantiated me..");
    }
}

public class Driver {
    public static void main(String[] args) {
        System.out.println(new MyClass(this.getClass().getName())); // should print Driver but no quotes should be there in parameter
    }
}

edited Jul 02 '15 at 07:25

AnkeyNigam

2,810
4
15
23

answered Jul 02 '15 at 07:20

Kushal

8,100
9
63
82

well... this works but I wouldn't have had to ask if I could do this :) – bohanl Jul 02 '15 at 07:22
yes.. you can do this.. one error was in my previous post.. you should remove `final` with `whoCreatedMe` – Kushal Jul 02 '15 at 07:23

user140547 · Answer 3 · 2015-07-02T07:48:32.280

In plain Java, you could try to use the Stack Trace to get that kind of information. Of course, you should not hard-code 2, and it is probably quite fragile, and it may not work when you are using proxies, interceptors etc. you could put this in the constructor

        StackTraceElement[] stackTrace =  Thread.currentThread().getStackTrace();
        System.out.println(stackTrace[2].getClassName());

As for google-reflections which you mentioned in your tags, I don't think it supports such operations as this is not reflection.

score 0 · Answer 4 · answered Jul 02 '15 at 07:41

I would not suggest this method but, if you really want to do that, here is a working example that I could think of.

public class Driver {
     public static void main(String[] args) {
            System.out.println(new MyClass().whoCreatedMe); // should print Driver
        }
}


public class MyClass {

    public String whoCreatedMe;

    public MyClass(){
        Exception ex = new Exception();
        StackTraceElement[] stackTrace = ex.getStackTrace();
        whoCreatedMe = stackTrace[1].getClassName();
    }

}

Java - determine where an object is instantiated from object's class

4 Answers4