How do you get the object reference of an object in java when toString and hashCode have been overridden

Question

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

User · Answer

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.

User · Answer

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

User · Answer

What exactly are you planning on doing with it  what you want to do makes a difference with what you will need to call    hashCode  as defined in the JavaDocs  says       As much as is reasonably practical  the hashCode method defined by class Object does return distinct integers for distinct objects   This is typically implemented by converting the internal address of the object into an integer  but this implementation technique is not required by the Java trade  programming language     So if you are using hashCode   to find out if it is a unique object in memory that isn t a good way to do it   System identityHashCode does the following      Returns the same hash code for the given object as would be returned by the default method hashCode    whether or not the given object s class overrides hashCode    The hash code for the null reference is zero    Which  for what you are doing  sounds like what you want    but what you want to do might not be safe depending on how the library is implemented

User · Answer

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

User · Answer

This is how I solved it   Integer toHexString System identityHashCode object

User · Answer

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

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

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