How to get the previous key/value and the next key/value in Maps

Question

for (Entry entry : map.entrySet()) { 
        Double key = entry.getKey(); 
        String value = entry.getValue(); 

        // double nextKe         


        

Answer 1

You can use NavigableMap for this, which entrySet()'s iterator return entries in ascending key order:

NavigableMap myMap = new TreeMap<>();

//...

for (Map.Entry e : myMap.entrySet()) {
    Map.Entry next = myMap.higherEntry(e.getKey()); // next
    Map.Entry prev = myMap.lowerEntry(e.getKey());  // previous

   // do work with next and prev
}

Every entry retrieval is O(logN), so for full iteration this is not the most effective approach. To be more effective, on iteration just remember last 3 entries, and use 1st as prev, 2nd as current and 3rd as next, as @Malt suggests.