How to creat an Server-Client Application using the DatagramPacket and DatagramSocket classes?

As the question say, how may I create a server- client application using DatagramPacket and DatagramSocket ?

See the following solution:

import java.util.ArrayList;
import java.util.Collections;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Map;

public class DFSTree {

    public static ArrayList<Integer> listeIDsOrder = new ArrayList<>();

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

        map.put (1, null);   //root
        map.put (10, 1);
        map.put (11, 10);
        map.put (12, 10);
        map.put (13, 10);

        map.put (20, 1);
        map.put (21, 20);
        map.put (22, 20);

        map.put (30, 1);
        map.put (31, 30);

        getOrder (1, map);
        System.out.println (listeIDsOrder);
    }

    public static void getOrder (int root, Map<Integer, Integer> graph){

        LinkedList<Integer> stack = new LinkedList<>(); //use stack for correct order of processing
        stack.add(root); //add root
        getOrder(graph, stack);
    }

    public static void getOrder (Map<Integer, Integer> graph, LinkedList<Integer> stack ){

        while(!stack.isEmpty()){

            int node =  stack.pollFirst(); //for bfs order. for dfs order use stack.pollLast();
            listeIDsOrder.add(node);

             List<Integer> keys = new ArrayList<>(graph.keySet());
             Collections.sort(keys);

            for(int key : keys){
                if(graph.get(key) != null && graph.get(key) == node) {
                    stack.add(key);
                }
            }
        }
    }
}

Output: [1, 10, 20, 30, 11, 12, 13, 21, 22, 31]