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alternate solutions to "JDA Member may not be null" error

I'm trying to make it so when someone with the role "Owner" types the mute command, it takes the person they #mentioned and gives them the "Muted" role.
The rest of the code works on it's own, the only part that is not working is the line
event.getGuild().addRoleToMember(member,event.getGuild().getRoleById(0)).complete();
and the variable "member" is defined by
Member member = event.getGuild().getMemberById(mentionid);
The full chunk of code is:
package radishmouse.FoodWorld.Events;
import net.dv8tion.jda.api.EmbedBuilder;
import net.dv8tion.jda.api.entities.Member;
import net.dv8tion.jda.api.events.message.guild.GuildMessageReceivedEvent;
import net.dv8tion.jda.api.hooks.ListenerAdapter;
import radishmouse.FoodWorld.FoodWorld;
public class GuildMessageReceived extends ListenerAdapter {
public void onGuildMessageReceived(GuildMessageReceivedEvent event) {
String[] args = event.getMessage().getContentRaw().split("\\s+");
if (args[0].equalsIgnoreCase(FoodWorld.prefix + "mute")) {
if (hasRole("Owner", event)) {
if (args.length == 2) {
String mentionid = args[1].replace("<#!", "").replace(">", "");
Member member = event.getGuild().getMemberById(mentionid);
event.getGuild().addRoleToMember(member, event.getGuild().getRoleById(0)).complete();
EmbedBuilder msg = FoodWorld.sendMessage(null, "idk " + mentionid + member, "Blue");
event.getChannel().sendMessageEmbeds(msg.build()).queue();
}
else {
EmbedBuilder msg = FoodWorld.sendMessage("Specify Who To Mute", "Usage: " + FoodWorld.prefix + "mute [#mention who to mute]", "Blue");
event.getChannel().sendMessageEmbeds(msg.build()).queue();
}
}
}
/* If the bot ever sends a message, then add a ❌ reaction so users can delete that message */
if (event.getAuthor().equals(event.getJDA().getSelfUser())) {
event.getMessage().addReaction("❌").queue();
}
}
private boolean hasRole(String string, GuildMessageReceivedEvent event) {
Boolean toReturn = false;
for(int i=0; i < event.getMember().getRoles().size(); i++){
if("Owner".equals(event.getMember().getRoles().get(i).getName())){
toReturn = true;
}
}
return toReturn;
}
For reference, I'm following this tutorial on youtube: tutorial.
I'm not the most familiar with JDA and don't know how this would be done in an easier way.

Instead of parsing the string:
String mentionid = args[1].replace("<#!", "").replace(">", "");
Member member = event.getGuild().getMemberById(mentionid);
Use getMentionedMembers:
List<Member> mentions = event.getMessage().getMentionedMembers();
if (mentions.isEmpty()) {
EmbedBuilder msg = FoodWorld.sendMessage("Specify Who To Mute", "Usage: " + FoodWorld.prefix + "mute [#mention who to mute]", "Blue");
event.getChannel().sendMessageEmbeds(msg.build()).queue();
} else {
Member member = mentions.get(0);
event.getGuild().addRoleToMember(member, event.getGuild().getRoleById(0)).queue();
EmbedBuilder msg = FoodWorld.sendMessage(null, "idk " + member.getId() + member, "Blue");
event.getChannel().sendMessageEmbeds(msg.build()).queue();
}

How to get the command sender from the Commands class to the DB class

I have two classes of DB in which there is a method "GetMoney" and Commands
In general, the point is that in the DB class I need to somehow get a player, or rather the sender of the command that is written in the Commands class. How can I do this?
//DB - GETMONEY
public int GetMoney(String name) throws Exception {
String tableName = this.plugin.getConfig().getString("tableName");
String dbNames = this.plugin.getConfig().getString("columnFirst");
String dbBalance = this.plugin.getConfig().getString("columnSecond");
Connection c = this.getConnection();
Statement s = c.createStatement();
ResultSet res = s.executeQuery("SELECT " + dbBalance +" FROM "+ tableName +" WHERE " + dbNames +" = '"+ name +"'" );
res.next();
return res.getInt(dbBalance);
}
//COMMANDS - onCommand
#Override
public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
String name = sender.getName();;
if(args.length == 0 ) {
String showBalance = this.plugin.getConfig().getString("messages.showBalance");
try {
int balance = this.database.GetMoney(name);
showBalance = showBalance.replace("&", "\u00a7").replace("_nm", name).replace("_bl", String.valueOf(balance));
sender.sendMessage(showBalance);
} catch (Exception e) {
e.printStackTrace();
}
return false;
}

I think passing Player interface is better than a simple name. First you have to make sure the sender is a Player not a ConsoleCommandSender. After this you can pass the Player and in the GetMoney() method you simply get the player's name with player.getName() method.
EDIT: I saw you need the command sender. You can pass it too instead of player just replace GetMoney parameter with CommandSender and delete instance check where we determine the sender is a player or not. After all you simply check it again wherever you want and cast it to Player again.
#Override
public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
if (args.length == 0) {
if (sender instanceof Player) {
Player player = (Player) sender;
String showBalance = this.plugin.getConfig().getString("messages.showBalance");
try {
int balance = this.database.GetMoney(player);
showBalance = showBalance.replace("&", "\u00a7").replace("_nm", player.getName()).replace("_bl", String.valueOf(balance));
sender.sendMessage(showBalance);
} catch (Exception e) {
e.printStackTrace();
}
} else {
sender.sendMessage("Player only command.");
}
}
return false;
}
//DB - Getmoney
public int GetMoney(Player player) throws Exception {
String tableName = this.plugin.getConfig().getString("tableName");
String dbNames = this.plugin.getConfig().getString("columnFirst");
String dbBalance = this.plugin.getConfig().getString("columnSecond");
Connection c = this.getConnection();
Statement s = c.createStatement();
ResultSet res = s.executeQuery("SELECT " + dbBalance +" FROM "+ tableName +" WHERE " + dbNames +" = '"+ player.getName() +"'" );
res.next();
return res.getInt(dbBalance);
}

Does this contain Polymorphic references? If not, how could it be implemented?

I am not too familiar with polymorphism, and was wondering if I have it used in my code?
If this doesn't contain a polymorphic reference, could you lead me in a direction of where I would need to go? The files that the program is using are not included, as I am mainly curious about whether or not any polymorphic references are used.
java file 1 - this file runs the program
import java.util.Scanner;
public class ADTDemo {
ADTDictionary dictionary;
public static void menu() {
System.out.println("Welcome the Faculty Directory Program");
System.out.println(" Use commands:");
System.out.println(" list all");
System.out.println(" list DEPT_NAME");
System.out.println(" add DEPT_NAME, FIRST LAST");
System.out.println(" remove DEPT_NAME, FIRST LAST");
System.out.println(" exit");
}
public static void main(String[] args) {
menu();
String command;
ADTDemo dictObj = new ADTDemo();
dictObj.dictionary = new ADTDictionary();
dictObj.dictionary.read();
Scanner scanner = new Scanner(System.in);
do {
System.out.println("");
System.out.print(">>");
command = scanner.nextLine().trim();
if (!command.equals("exit")) {
dictObj.action(command);
} else {
dictObj.dictionary.saveEntries();
System.out.println("Goodbye! Have a nice day!");
}
} while (!command.equalsIgnoreCase("exit"));
}
public void action(String command) {
if (command.equalsIgnoreCase("LIST ALL")) {
dictionary.listAll();
return;
}
else if (command.toUpperCase().contains("LIST")) {
if (command.length() == 4){
System.out.println("Command needed.");
return;
}
command = command.substring(5, command.length());
dictionary.listDeptName(command);
return;
}
else if (command.toUpperCase().contains("ADD")) {
command = command.substring(4, command.length());
dictionary.add(command);
return;
}
else if (command.toUpperCase().contains("REMOVE")) {
command = command.substring(6, command.length());
dictionary.remove(command);
}
}
}
java file 2
import java.io.File;
import java.io.FileNotFoundException;
import java.io.IOException;
import java.io.PrintWriter;
import java.util.ArrayList;
import java.util.HashMap;
import java.util.List;
import java.util.Map;
import java.util.Scanner;
public class ADTDictionary {
Map<String, List<String>> adtDictionary;
public void read() {
try {
File facultyFile = new File("faculty.txt");
File departmentFile = new File("departments.txt");
Scanner departmentScanner = new Scanner(departmentFile);
Scanner facultyScanner = new Scanner(facultyFile);
adtDictionary = new HashMap<String, List<String>>();
while (departmentScanner.hasNextLine()) {
String department = departmentScanner.nextLine().trim();
adtDictionary.put(department, new ArrayList<String>());
}
while (facultyScanner.hasNextLine()) {
String faculty = facultyScanner.nextLine();
String[] values = faculty.split(",");
adtDictionary.get(values[1].trim()).add(values[0]);
}
} catch (FileNotFoundException ex) {
System.out.println("ERROR: File not found.");
}
}
public void listAll() {
for (String key : adtDictionary.keySet()) {
for (String value : adtDictionary.get(key)) {
System.out.println(value + ", " + key);
}
}
}
public void listDeptName(String department) {
if (null != adtDictionary.get(department)) {
for (String name : adtDictionary.get(department)) {
System.out.println(name);
}
}
else{
System.out.println("Unknown entry made.");
}
}
public void add(String value) {
if(!value.contains(",")){
System.out.println("Incorrect entry.");
return;
}
String[] values = value.split(",");
String dept = values[0].trim();
String faculty = values[1].trim();
String[] facName = faculty.split(" ");
if (!(facName.length == 2)){
System.out.println("Please only enter First and Last name of faculty member.");
return;
}
if (!(null != adtDictionary.get(dept))) {
if(adtDictionary.containsKey(dept.toUpperCase())){
System.out.println("Incorrect departtment entry.");
return;
}
else if (dept == dept.toUpperCase()){
adtDictionary.put(dept, new ArrayList<String>());
}
else{
System.out.println("Incorrect department entry.");
return;
}
}
for (String name : adtDictionary.get(dept)) {
if (name.equalsIgnoreCase(faculty)) {
System.out.println("Cannot add " + name + " to " + dept + " because they already exist there.");
return;
}
}
adtDictionary.get(dept).add(faculty);
System.out.println("OK, added " + faculty);
}
public void remove(String value) {
String[] values = value.split(",");
String dept = values[0].trim();
String faculty = values[1].trim();
adtDictionary.get(dept).remove(faculty);
System.out.println("OK, removed " + faculty + " from " + dept);
}
public void saveEntries(){
try {
File facultyFile = new File("faculty.txt");
File departmentFile = new File("departments.txt");
PrintWriter facWriter = new PrintWriter(facultyFile);
PrintWriter deptWriter = new PrintWriter(departmentFile);
for (Object s : adtDictionary.keySet()) {
deptWriter.println(s);
}
deptWriter.close();
for (String key : adtDictionary.keySet()) {
for (String value : adtDictionary.get(key)) {
facWriter.println(value + ", " + key);
}
}
facWriter.close();
}
catch (IOException ex){
System.out.println("ERROR saving file.");
}
}
}

Refactoring the adding process

public static void addToUserList(User newUser){
boolean hasFound = false;
for (User user : users) {
if(user.getUserID() == newUser.getUserID()){
System.out.println("DUPLICATED USER ID: " + user.getUserID() + "ALREADY EXISTS");
hasFound = true;
break;
}
}
if(hasFound = false){
users.add(newUser);
}
}
How do I refactor this code? In users arraylist, there shouldn't be duplicate users by ID.
I think using boolean variable is a bit unnecessary but I couldn't find any better solution.
P.Ss: Also if there is a convenion for these kind of coding styles, can you provide a name? Thank you.

You don't need the boolean, just return from the method if the user exists.
public static void addToUserList(User newUser){
for (User user : users) {
if(user.getUserID() == newUser.getUserID()){
System.out.println("DUPLICATED USER ID: " + user.getUserID() + "ALREADY EXISTS");
return;
}
}
users.add(newUser);
}

please try with this.Change the == in first if to != like below and remove the last part
public static void addToUserList(User newUser){
boolean hasFound = false;
for (User user : users) {
if(user.getUserID() != newUser.getUserID()){
users.add(newUser);
}
else{
System.out.println("DUPLICATED USER ID: " + user.getUserID() + "ALREADY EXISTS");
}
}
}

Number of kills is always the same for every player. (Bukkit)

As I was coding, I tested my plugin and this seemed to happen:
basically, when a player kills another player, his kill count goes up by one. However, when a player has for instance 5 kills, so will all the other players. Here is my code:
public class KillDeathCounter extends JavaPlugin {
public void onEnable() {
new PlayerListener(this);
getLogger().info("Players will not be able to kit spam.");
this.getConfig().addDefault("playerkills", 0);
this.getConfig().addDefault("playerdeaths", 0);
this.getConfig().options().copyDefaults(true);
saveConfig();
}
public void onDisable() {
getLogger().info("Kill Death Counter has been disabled.");
saveConfig();
}
public boolean onCommand(CommandSender sender, Command cmd, String label,
String[] args) {
if (cmd.getName().equalsIgnoreCase("digipvp")) {
Player p = (Player) sender;
p.sendMessage(ChatColor.AQUA
+ "Our PVP plugin was developed by Pierre Lichtlé, the owner, also known as Master Digi."
+ " If you would like to contact him for a plugin, send him an email at developer.petlamb#gmail.com."
+ " Thanks for playing on our server!");
return true;
}
return false;
}
}
package me.katsunicalis.plugin;
import org.bukkit.ChatColor;
import org.bukkit.Statistic;
import org.bukkit.entity.Entity;
import org.bukkit.entity.Player;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.entity.EntityDeathEvent;
import org.bukkit.event.entity.PlayerDeathEvent;
public class PlayerListener implements Listener {
KillDeathCounter kdc;
public PlayerListener(KillDeathCounter plugin) {
plugin.getServer().getPluginManager().registerEvents(this, plugin);
kdc = plugin;
}
#EventHandler
public void playerKillsPlayer(EntityDeathEvent e) {
Entity deade = e.getEntity();
Entity killer = e.getEntity().getKiller();
if (killer instanceof Player && deade instanceof Player){
int kills = kdc.getConfig().getInt("playerkills");
int deaths = kdc.getConfig().getInt("playerdeaths");
kdc.getConfig().set("playerkills", kills += 1);
kdc.getConfig().set("playerdeaths", deaths += 1);
killer.sendMessage("You now have " + kills + " kills!");
deade.sendMessage("You now have " + deaths + " deaths!");
}
}
}
Thanks very much guys! :)

The problem is that you're increasing the same variable for every time a player kills another player. To fix this, you should use a different variable for each player, for example "kills.playerUUIDHere" and "deaths.playerUUIDHere".
To get a player's UUID, you can use player.getUniqueId(), then to get the String representation of the UUID, you could use uuid.toString(). So, you could do something like this to change a player's kills:
String uuid = player.getUniqueId().toString();
int kills = kdc.getConfig().getInt("playerkills." + uuid);
kdc.getConfig().set("playerkills." + uuid, kills += 1);
The same logic can be used for deaths, so, you could use something like this for your playerKillsPlayer() method:
#EventHandler
public void playerKillsPlayer(EntityDeathEvent e) {
Entity dead = e.getEntity();
Entity killer = e.getEntity().getKiller();
if(killer instanceof Player && dead instanceof Player){
String killerUUID = ((Player) killer).getUniqueId().toString();
String deadUUID = ((Player) dead).getUniqueId().toString();
int kills = kdc.getConfig().getInt("playerkills." + killerUUID);
int deaths = kdc.getConfig().getInt("playerdeaths." + deadUUID);
kdc.getConfig().set("playerkills." + killerUUID + , kills += 1);
kdc.getConfig().set("playerdeaths." + deadUUID, deaths += 1);
killer.sendMessage("You now have " + kills + " kills!");
dead.sendMessage("You now have " + deaths + " deaths!");
}
}