In the Entity Relation example datastructures, calling .hashcode on any of the items causes an StackOverflow due to unbounded recursion.

• ConllRawSentence - Calls .hashcode on tokens and relations in the sentence.
• ConllRawToken - Calls .hashcode on the sentence object.
• ConllRelation - Calls .hashcode on its two entity tokens and sentence object.

This leads to unbounded recursion. Thus, cannot add these instances in a HashSet or HashMap (as keys).