example for EasternGamer#7339

RolePrefixes.java

import sx.blah.discord.handle.impl.events.guild.channel.message.MessageReceivedEvent;
import sx.blah.discord.handle.obj.IGuild;
import sx.blah.discord.handle.obj.IRole;
import sx.blah.discord.handle.obj.IUser;

import java.util.LinkedHashMap;
import java.util.List;

public class RolePrefixes {

    // LinkedHashMap maintains the order in which you add elements
    // you will initialise this at startup of your bot possibly
    public static LinkedHashMap<IRole, String> rolesPrefixes;

    public void updateEveryone(MessageReceivedEvent event) {

        IGuild guild = event.getGuild();

        List<IUser> users = guild.getUsers();

        // this operation will be applied to all users of the guild
        users.forEach(user -> {
            // here we go through all roles with a prefix in order, and get the first one that our user has
            // in case the user has none of these roles, we return null
            IRole userRoleWithPrefix = rolesPrefixes.keySet().stream().filter(role -> user.hasRole(role)).findFirst().orElse(null);

            if (userRoleWithPrefix != null) {
                // we get the prefix from our map
                String prefix = rolesPrefixes.get(userRoleWithPrefix);

                // assuming there's a space between prefix and name
                guild.setUserNickname(user, prefix + " " + user.getName());
            }
        });
    }
}