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

public class Suggestion {

    class Mom{
        Map<String,Mom> data= new HashMap<>();
    }

    Mom tree = new Mom();
    
    public void input(String s){
        System.out.println("nnn : "+tree.data.keySet());
        String[] mots = s.split(" ");
        Mom current= tree;
        for (String mot: mots){
            current.data.putIfAbsent(mot,new Mom());
            current = current.data.get(mot);
        }
        print();
    }

    public void print() {
        System.out.println("bbb : "+tree.data.keySet());
        printHelper(tree, 0);
    }

    private void printHelper(Mom node, int depth) {
        for (Map.Entry<String, Mom> entry : node.data.entrySet()) {
            for (int i = 0; i < depth; i++) {
                System.out.print("    ");
            }
            System.out.println(entry.getKey());
            printHelper(entry.getValue(), depth + 1);
        }
    }

    public List<String> get(String s) {
        System.out.println("aaaaaaaaaaaaaaaaa "+s);
        Mom current = tree;
        System.out.println("vvvvvvv : "+tree.data.keySet());
        for (String str : s.split(" ")) {
            System.out.println(str+" : " +current.data.keySet());
            if (!current.data.containsKey(str)) {
                System.out.println(" : done");
                return new ArrayList<>();
            } else {
                System.out.println(" : forward");
                current = current.data.get(str);
            }
        }
        return new ArrayList<>(current.data.keySet());
    }
}

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

public class Suggestion {

    class Mom{
        Map<String,Mom> data= new HashMap<>();
    }

    Mom tree = new Mom();
    
    public void input(String s){
        System.out.println("nnn : "+tree.data.keySet());
        String[] mots = s.split(" ");
        Mom current= tree;
        for (String mot: mots){
            current.data.putIfAbsent(mot,new Mom());
            current = current.data.get(mot);
        }
        print();
    }

    public void print() {
        System.out.println("bbb : "+tree.data.keySet());
        printHelper(tree, 0);
    }

    private void printHelper(Mom node, int depth) {
        for (Map.Entry<String, Mom> entry : node.data.entrySet()) {
            for (int i = 0; i < depth; i++) {
                System.out.print("    ");
            }
            System.out.println(entry.getKey());
            printHelper(entry.getValue(), depth + 1);
        }
    }

    public List<String> get(String s) {
        System.out.println("aaaaaaaaaaaaaaaaa "+s);
        Mom current = tree;
        System.out.println("vvvvvvv : "+tree.data.keySet());
        for (String str : s.split(" ")) {
            System.out.println(str+" : " +current.data.keySet());
            if (!current.data.containsKey(str)) {
                System.out.println(" : done");
                return new ArrayList<>();
            } else {
                System.out.println(" : forward");
                current = current.data.get(str);
            }
        }
        return new ArrayList<>(current.data.keySet());
    }
}

Suggestion sug = new Suggestion();
sug.input("feur baka feur");
List<String> j = sug.get("feur baka");
Bukkit.broadcastMessage(j+""); 

Suggestion sug = new Suggestion();
sug.input("feur baka feur");
List<String> j = sug.get("feur baka");
Bukkit.broadcastMessage(j+"");