Unknown Bug

Hello Bukkit,
I am writing a group plugin. It will be used for permission management on my server.
However, when I execute the command /group (or /group <player_name>), all it says is, that the given player is in the "leather"-group, even though the player is in another group. (Source code not formatted correctly. Don't know how to though. See files for right formatting.)
Maybe Bukkit can help me.

Stym.java:

Code:

import org.bukkit.plugin.java.JavaPlugin;

public class Stym extends JavaPlugin {

  @Override
  public void onEnable() {
  getConfig().options().copyDefaults(true);
  saveConfig();
  registerCommands();
  registerListeners();

  }

  public void registerCommands() {
  GroupCommand groupCommandClass = new GroupCommand(this);
  getCommand("GROUP").setExecutor(groupCommandClass);

  }

  public void registerListeners() {

  }

  public boolean isLeather(String playerName) {
  for(String ironPlayerName : getConfig().getStringList("groups.iron")) {
  if(!ironPlayerName.equals(playerName)) {
  for(String diamondPlayerName : getConfig().getStringList("groups.diamond")) {
  return !diamondPlayerName.equals(playerName);

  }

  } else {
  return false;

  }

  }

  return false;

  }

  public boolean isIron(String playerName) {
  for(String ironPlayerName : getConfig().getStringList("groups.iron")) {
  if(ironPlayerName.equals(playerName)) {
  for(String diamondPlayerName : getConfig().getStringList("groups.diamond")) {
  return !diamondPlayerName.equals(playerName);

  }

  } else {
  return false;

  }

  }

  return false;

  }

  public boolean isDiamond(String playerName) {
  for(String ironPlayerName : getConfig().getStringList("groups.iron")) {
  if(!ironPlayerName.equals(playerName)) {
  for(String diamondPlayerName : getConfig().getStringList("groups.diamond")) {
  return diamondPlayerName.equals(playerName);

  }

  } else {
  return false;

  }

  }

  return false;

  }

}

GroupCommand.java:

Code:

import org.bukkit.entity.Player;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.command.CommandExecutor;

public class GroupCommand implements CommandExecutor {

  Stym stym;

  GroupCommand(Stym stymClass) {
  stym = stymClass;

  }

  @Override
  public boolean onCommand(CommandSender sender, Command command, String label, String[] arguments) {
  if(arguments.length == 0) {
  if(sender instanceof Player) {
  if(!sender.isOp()) {
  if(stym.isLeather(sender.getName())) {
  sender.sendMessage("You are made out of leather!");

  } else if(stym.isIron(sender.getName())) {
  sender.sendMessage("You are made out of iron!");

  } else {
  sender.sendMessage("You are made out of diamond!");

  }

  } else {
  sender.sendMessage("You are an operator!");

  }

  } else {
  sender.sendMessage("You are a god!");

  }

  } else if(arguments.length == 1) {
  if(!arguments[0].equals("Krischon")) {
  if(stym.isLeather(sender.getName())) {
  sender.sendMessage(arguments[0] + " " + "is made out of leather!");

  } else if(stym.isIron(sender.getName())) {
  sender.sendMessage(arguments[0] + " " + "is made out of iron!");

  } else {
  sender.sendMessage(arguments[0] + " " + "is made out of diamond!");

  }

  } else {
  sender.sendMessage("Krischon is an operator!");

  }

  } else {
  sender.sendMessage("Not supported yet!");

  }

  return true;

  }

}

plugin.yml:

Code:

name: Stym
main: Stym
version: 1.3.3.7
  commands:
  group:

config:

Code:

groups:
  iron:
    - Player
    - Another_Player
  diamond:
    - Rich_Player