[java] How do you get the "object reference" of an object in java when toString() and hashCode() have been overridden?

I would like to print the "object reference" of an object in Java for debugging purposes. I.e. to make sure that the object is the same (or different) depending on the situation.

The problem is that the class in question inherits from another class, which has overriden both toString() and hashCode() which would usually give me the id.

Example situation: Running a multi-threaded application, where I (during development) want to check if all the threads use the same instance of a resource object or not.

Double equals == will always check based on object identity, regardless of the objects' implementation of hashCode or equals. Of course - make sure the object references you are comparing are volatile (in a 1.5+ JVM).

If you really must have the original Object toString result (although it's not the best solution for your example use-case), the Commons Lang library has a method ObjectUtils.identityToString(Object) that will do what you want. From the JavaDoc:

public static java.lang.String identityToString(java.lang.Object object)

Gets the toString that would be produced by Object if a class did not override toString itself. null will return null.

 ObjectUtils.identityToString(null)         = null
 ObjectUtils.identityToString("")           = "java.lang.String@1e23"
 ObjectUtils.identityToString(Boolean.TRUE) = "java.lang.Boolean@7fa"

You cannot safely do what you want since the default hashCode() may not return the address, and has been mentioned, multiple objects with the same hashCode are possible. The only way to accomplish what you want, is to actually override the hashCode() method for the objects in question and guarantee that they all provide unique values. Whether this is feasible in your situation is another question.

For the record, I have experienced multiple objects with the same default hashcode in an IBM VM running in a WAS server. We had a defect where objects being put into a remote cache would get overwritten because of this. That was an eye opener for me at that point since I assumed the default hashcode was the objects memory address as well.

Add a unique id to all your instances, i.e.

public interface Idable {
  int id();
}

public class IdGenerator {
  private static int id = 0;
  public static synchronized int generate() { return id++; }
}

public abstract class AbstractSomething implements Idable {
  private int id;
  public AbstractSomething () {
    this.id = IdGenerator.generate();
  }
  public int id() { return id; }
}

Extend from AbstractSomething and query this property. Will be safe inside a single vm (assuming no game playing with classloaders to get around statics).

we can simply copy the code from tostring of object class to get the reference of string

class Test
{
  public static void main(String args[])
  {
    String a="nikhil";     // it stores in String constant pool
    String s=new String("nikhil");    //with new stores in heap
    System.out.println(Integer.toHexString(System.identityHashCode(a)));
    System.out.println(Integer.toHexString(System.identityHashCode(s)));
  }
}

This is how I solved it:

Integer.toHexString(System.identityHashCode(object));