Convert Set> to HashMap

Question

At one point in my code, I created a Set> from a map. Now I want to recreate the same map form, so I want to convert the HashS

Answer 1

These are some toMap utility in common libraries, but unfortunately none of them support Set directly so you need to do Set#toArray() first. (I left out Guava for Neil's answer which is arguably the best)

Commons Lang's ArrayUtils.toMap

Map map = ArrayUtils.toMap(entrySet.toArray());

// to recover the type...
@SuppressWarnings("unchecked")
Map typedMap = (Map)(Map)map;

Commons Collections' MapUtils.putAll

Map map = MapUtils.putAll(new HashMap(), entrySet.toArray());

Java 9's Map.ofEntries

 // convert to array and recover the type...
 @SuppressWarnings("unchecked")
 Map map = Map.ofEntries(entrySet.toArray(new Map.Entry[0]));

 // You need to copy again if you want a mutable one
 Map hashmap = new HashMap<>(map);