Java Reference
In-Depth Information
b. Given a
Stream
where each element is a word, count the number of times each
word appears. So, if you were given the following input, you would return a
Map
of
[John → 3, Paul → 2, George → 1]
:
Stream
<
String
>
names
=
Stream
.
of
(
"John"
,
"Paul"
,
"George"
,
"John"
,
"Paul"
,
"John"
);
c. Implement
Collectors.groupingBy
as a custom collector. You don't need to
provide a downstream collector, so just implementing the simplest variant is
fine. If you look at the JDK source code, you're cheating! Hint: you might
want to start with
public class GroupingBy<T, K> implements Collect-
or<T, Map<K, List<T>>, Map<K, List<T>>>
. This is an advanced exercise,
so you might want to attempt it last.
3.
Map enhancements.
Efficiently calculate a Fibonacci sequence using just the
computeIfAbsent
method
on a
Map
. By “efficiently,” I mean that you don't repeatedly recalculate the Fibonacci
sequence of smaller numbers.
