Challenge: Build a Custom Collector for Category Counting
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You need to implement a custom Collector
that processes a list of products and counts how many products belong to each category.
- In the
supplier()
method, return a newHashMap
. - In the
accumulator()
method, call theget()
method on theproduct
map to retrieve the value of the"category"
key and pass it as the first parameter of themerge()
method. - For the second parameter in the same method, provide the initial value (
1
). - In the
combiner()
method, pass thekey
ofmap2
as the first parameter of themerge()
method. - For the second parameter in the same method, pass the
value
of themap2
. - In the
finisher()
method, return themap
without modifying it using a lambda. - In the
characteristics()
method, return a set that ensures the collection remains unchanged (IDENTITY_FINISH
). - In the
collect()
method, pass the implementation of theCollector
interface (CategoryCountCollector
).
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solution
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