java - generate unique md5 hash for objects

Question

I need to generate unique hash for objects to identify objects with the same exact attributes.

After reading a bit on the subject I decided its best to use MD5 hashing rather than java hashCode (I have a large number of objects, around 200,000-300,000).

I found many examples on how to do MD5 hashing on a string, but didn't find how to do it on an object, so that it will really be unique according to the object's attributes.

Answer 1

Hash code of an object does not need to be unique. By the way it is impossible

Hash code must comply to the following contract:

• It should return the same value every time it is invoked on the same object in the same state.
• If two objects are equal according to Object::equals then the hashCode should return the same.

Most of IDEs can generate the method hashCode() but there are some tools even in JDK for generating hashcode eg. java.util.Objects.hash(Object...) .

You can read a great summary here