Splitting a Hashmap into two smaller maps

Question

I have one hashmap with K, V value of and that I want to split into two subMaps.

HashMap<Long,JSONObject>

One way is this I have found that we can use treemap and do subMapping.

TreeMap<Integer, Integer> sorted = new TreeMap<Integer, Integer>(bigMap);

SortedMap<Integer, Integer> zeroToFortyNine = sorted.subMap(0, 50);
SortedMap<Integer, Integer> fiftyToNinetyNine = sorted.subMap(50, 100);

But the thing is I am not getting subMap for jsonObject and I want to do it with HashMap only.

Thanks

Answer 1

You can make use of the Java 8 Streaming API:

Map<Long, JSONObject> map = ...;
AtomicInteger counter = new AtomicInteger(0);
Map<Boolean, Map<Long, JSONObject>> collect = map.entrySet()
    .stream()
   .collect(Collectors.partitioningBy(
       e -> counter.getAndIncrement() < map.size() / 2, // this splits the map into 2 parts
       Collectors.toMap(
           Map.Entry::getKey, 
           Map.Entry::getValue
       )
   ));

This collects the map into 2 halfes, the first (map.get(true)) containing all the elements from below the middle and the second (map.get(false)) half containing all the elements from the middle upwards.