如何获取树形图的最后n个元素

Question

I have a TreeMap, that looks like this:

 TreeMap<Instant, HashMap<Type, Double>>

The Instant values are representing hours of a day; for each passed hour a value is stored in my map. Now I would like to get the last 24 elements (so the hours of the passed day) of this map. How could I do that?

Cheers

Answer 1

使用TreeMap.tailMap（） 。

Answer 2

You can use the descendingMap call to get a view on the map which is basically in the reverse order, then take the first 24 entries from that (call iterator etc). ( Guava 's Iterables provides helpful methods for limiting an iterable etc.)

EDIT: For example, to get the last 24 elements (in reverse order, and using Guava) you could use:

List<HashMap<Type, Double>> lastValues = Lists.newArrayList
    (Iterables.limit(map.descendingMap().values(), 24));

Answer 3

您可以将其SortedMap<LocalDate, SortedMap<Hours, Map<Type, Double>>>以便从外部Map获取最新日期。