Sort Tree Map with Lambda Comparator

January 4, 2023

I have below class

public class Frequency {
    public int freq;
    public int val;
}

I want to sort the the TreeMap with Frequence.freq
How to do it.

TreeMap<Integer,Frequency> map = new TreeMap( (f1,f2) ->  f1. ) ;

// not able to access f1.freq /Frequency class variables arent visible

>Solution :

TreeMap keys are always sorted it means that this collection will not let you change the order. If you want to get sorted collection by freq value you can do something like:

public static void main(String[] args) {
        Map<Integer, Frequency> map = ....;

        List<Frequency> sortedList = map.values().stream().sorted(Comparator.comparingInt(o -> o.freq)).collect(toCollection(ArrayList::new));
}