TreeMap.get() return Null even key exists

Question

I am trying to get from TreeMap but it return null even the key exist. HashCode and eqauls is based on word only. Comparable is based on freqency.

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Answer 1

TreeMap uses the compareTo method to decide key ordering and key equality.

Since your Word class uses the freq field in its compareTo method, any two Words with the same freq are considered equal.

From the documentation of TreeMap:

... but a sorted map performs all key comparisons using its compareTo (or compare) method, so two keys that are deemed equal by this method are, from the standpoint of the sorted map, equal.