Why AbstractCollection does not implement equals()?

Question

Did you know that :

Map m1 = new HashMap();
Map m2 = new HashMap();
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Answer 1

Per the contract of Collection#equals(), there is no general-purpose equals() methods for Collections, and thus AbstractCollection cannot provide one.

Note that HashMap$Values is neither a Set nor a List, thus the quandary and in a sense the reason it does not support equals().