Minimum spanning tree - study code written in Java

MinimumSpanningTree.java

import java.util.*;
class Connection{
    String node1;
    String node2;
    int cost;
    public Connection(String a, String b, int c){
        node1 = a;
        node2 = b;
        cost = c;
    }
}
public class Solution {
    static class DisjointSet
    {
        Set<String> set;
        Map<String, String> map;
        int count;
        public DisjointSet()
        {
            count = 0;
            set = new HashSet<>();
            map = new HashMap<>();
        }
        public void MakeSet(String s)
        {
            if(!set.contains(s))
            {
                count++;
                set.add(s);
                map.put(s, s);
            }
        }
        public String Find(String s)
        {
            if(!set.contains(s)) return null;
            if(s.equals(map.get(s))) return s;
            String root = this.Find(map.get(s));
            map.put(s, root);
            return root;
        }
        public void Union(String s, String t)
        {
            if(!set.contains(s) || !set.contains(t)) return;
            if(s.equals(t)) return;
            count--;
            map.put(s, t);
        }
    }
    static class ConnectionComparator1 implements Comparator<Connection>
    {
        @Override
        public int compare(Connection a, Connection b)
        {
            return a.cost - b.cost;
        }
    }
    static class ConnectionComparator2 implements Comparator<Connection>
    {
        @Override
        public int compare(Connection a, Connection b)
        {
            if(a.node1.equals(b.node1)) return a.node2.compareTo(b.node2);
            else return a.node1.compareTo(b.node1);
        }
    }
    public static List<Connection> getMST(List<Connection> connections)
    {
         
        Comparator<Connection> comparator1 = new ConnectionComparator1();
        Comparator<Connection> comparator2 = new ConnectionComparator2();
        Collections.sort(connections, comparator1);
        DisjointSet set = new DisjointSet();
        List<Connection> res = new ArrayList<>();
        for(Connection itr: connections)
        {
            set.MakeSet(itr.node1);
            set.MakeSet(itr.node2);
        }
        for(Connection itr: connections)
        {
            String s = set.Find(itr.node1);
            String t = set.Find(itr.node2);
            if(!s.equals(t))
            {
                set.Union(s, t);
                res.add(itr);
                if(set.count == 1) break;
            }
        }
        if(set.count == 1)
        {
            Collections.sort(res, comparator2);
            return res;
        }
        else return new ArrayList<Connection>();
    }
 
    public static void main(String[] args) {
        // TODO Auto-generated method stub
        ArrayList<Connection> connections = new ArrayList<>();
//      connections.add(new Connection("Acity","Bcity",1));
//      connections.add(new Connection("Acity","Ccity",2));
//      connections.add(new Connection("Bcity","Ccity",3));
            connections.add(new Connection("A","B",6));
        connections.add(new Connection("B","C",4));
        connections.add(new Connection("C","D",5));
        connections.add(new Connection("D","E",8));
        connections.add(new Connection("E","F",1));
        connections.add(new Connection("B","F",10));
        connections.add(new Connection("E","C",9));
        connections.add(new Connection("F","C",7));
        connections.add(new Connection("B","E",3));
        connections.add(new Connection("A","F",1));
 
        List<Connection> res = getMST(connections);
        for (Connection c : res){
            System.out.println(c.node1 + " -> " + c.node2 + " cost : " + c.cost);
        }
    }
 
}