Check if two values are in the same key (Hashmap)

Hello, so I am making a party plugin and trying to check if two players are in the same part of a hashmap. I have tried multiple things but no luck here is all the code I have right now:

Code:

package me.endureblackout.partytime;

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

import org.bukkit.Bukkit;
import org.bukkit.ChatColor;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.entity.EntityDamageByEntityEvent;
import org.bukkit.plugin.java.JavaPlugin;

public class PartyTimeMain extends JavaPlugin implements Listener {
   
    public Map<String, List<String>> party = new HashMap<>();
    public ArrayList<String> members = new ArrayList<String>();
    public HashMap<String, String> waiting = new HashMap<String, String>();
   
    public void onEnable() {
        getLogger().info("PartyTime enabled!");
    }
   
    public void onDisable() {
        getLogger().info("PartyTime disabled!");
    }
   
    @EventHandler
    public void onPlayerDamagePlayer(EntityDamageByEntityEvent e) {
        if(e.getDamager() instanceof Player && e.getEntity() instanceof Player) {
            Player hit = (Player) e.getEntity();
            Player hitter = (Player) e.getDamager();
           
            Set<String> key = party.keySet();
            if(party.get(key.iterator()).contains(hit.getName()) && party.get(key.iterator()).contains(hitter.getName())) {
                e.setCancelled(true);
                hitter.sendMessage("You can't hit players in your party!");
            }
        }
    }

    @EventHandler
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
       
        if(cmd.getName().equalsIgnoreCase("party")) {
            if(args.length != 1) {
                sender.sendMessage("Not enough args!");
            }
            if(args.length == 1 && args[0].equalsIgnoreCase("create")) {
                Player p = (Player) sender;
                members.add(p.getName());
                party.put(p.getName(), members);
                sender.sendMessage("Party created!");
            } else if(args.length == 2 && args[0].equalsIgnoreCase("add")) {
                if(!(party.containsKey(sender.getName()))) {
                    sender.sendMessage(ChatColor.RED + "You are not the owner of the party or do not belong to a party");
                } else {
                    sender.sendMessage(ChatColor.GREEN + args[1] + " has been invited to the party!");
                    for(Player p : Bukkit.getOnlinePlayers()) {
                        if(p.getName() == args[1]) {
                            p.sendMessage("You were invited to a party by " + sender.getName());
                        }
                    }
                    waiting.put(args[1], sender.getName());
                }
            } else if(args.length == 1 && args[0].equalsIgnoreCase("accept")) {
                if(waiting.containsKey(sender.getName())) {
                    String partyName = waiting.get(sender.getName());
                    List<String> list = party.get(partyName);
                    list.add(sender.getName());
                    party.put(partyName, list);
                    waiting.remove(sender.getName());
                    sender.sendMessage(ChatColor.GREEN + "Party invite accepted!");
                   
                    for(Player p : Bukkit.getOnlinePlayers()) {
                        if(party.get(partyName).contains(p.getName())) {
                            p.sendMessage(ChatColor.GREEN + sender.getName() + " has joined the party!");
                        }
                    }
                }
            } else if(args.length == 1 && args[0].equals("check")) {
                if(!(party.containsKey(sender.getName()))) {
                    sender.sendMessage("You are not a party leader!");
                } else if(party.containsKey(sender.getName())) {
                    List<String> list = party.get(sender.getName());
                    sender.sendMessage(list + "");
                }
            } else if(args.length == 2 && args[0].equalsIgnoreCase("kick")) {
                if(party.containsKey(sender.getName()) && party.get(sender.getName()).contains(args[1])) {
                    party.get(sender.getName()).remove(args[1]);
                }
            }
        }
       
        return false;
        }

}

Here is where my issue is:

Code:

    @EventHandler
    public void onPlayerDamagePlayer(EntityDamageByEntityEvent e) {
        if(e.getDamager() instanceof Player && e.getEntity() instanceof Player) {
            Player hit = (Player) e.getEntity();
            Player hitter = (Player) e.getDamager();
           
            Set<String> key = party.keySet();
            if(party.get(key.iterator()).contains(hit.getName()) && party.get(key.iterator()).contains(hitter.getName())) {
                e.setCancelled(true);
                hitter.sendMessage("You can't hit players in your party!");
            }
        }
    }

 

Why not store a Player -> Party relation? You can just check if player.getParty().equals(otherPlayer.getParty()) for example.

 

But ofc, use UUIDs instead of Players

 

@Lolmewn @MCMastery

You could, but I think a Set of "Party" Objects, each containing a Set of UUIDs would make the most sense here. I understand this turns the lookup into a O(n) lookup, but from a data perspective it makes the most sense, as likely you will most often be dealing with the group as a whole. If you're most often doing the other lookup (which party a player is in), then you should do what they said, for simplicity's sake.
@EndureBlackout

 

@mythbusterma Muh, it's memory versus CPU cycles. In my opinion CPU cycles always win the argument in such a case.

Of course.

 

Lemme see.. Two things under the same key...
Heres the code

public boolean isSameKey(Map map, Object o1, Object o2){
return false;
}

Very fast and simple function.
</sarcasm>
Jokes asside, map cannot have two of the same key. Youre better off having a UUID, String map where UUID is the player UUID and String is their party name, or even better, UUID, UUID so you save party UUIDs

 

@ArsenArsen *UUID, Set<UUID>
The user wants multiple people not just 1 in the party

 

No. PlayerUUID, PartyUUID was my idea.

 

@ArsenArsen @bwfcwalshy @EndureBlackout

Solution: Make a Party class.

 

@Lolmewn

It's a case of having the data structure that makes the most sense, which is far, far, far more important than a couple hundred cycles.