Bukkit - NullPointerException

Question

When executing the command "/group" and "/group example_player", I get a NullPointerException. It doesn't give me any more information, of what (or where) the problem is. I hope, that StackOverflow can help.

Stym.java:

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:

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) {

    }

    @Override
    public boolean onCommand(CommandSender sender, Command command, String label, String[] arguments) {
        try {
            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!");

            }

        } catch(Exception exception) {
            System.out.println(exception);

        }

        return true;

    }

}

plugin.yml:

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

config.yml:

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

Possible duplicate of [What is a Null Pointer Exception, and how do I fix it?](http://stackoverflow.com/questions/218384/what-is-a-null-pointer-exception-and-how-do-i-fix-it) — Ferrybig, Jan 11 '16 at 15:05

Calvin P. · Accepted Answer · 2015-11-08T22:32:34.657

Stym stym;

GroupCommand(Stym stymClass) {

}

You never initialized Stym stym in the constructor. Therefore, when you try to use it in your methods, it is null.

Stym stym;

GroupCommand(Stym stymClass) {
    stym = stymClass;
}

For loop

for(String diamondPlayerName : getConfig().getStringList("groups.diamond")) {
    return !diamondPlayerName.equals(playerName);

}

The way you have these loops set up, they will only evaluate the first name in the list and return the corresponding boolean value. The moment you return a value, the method will terminate. You'd be better off using something like this:

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

This way it will run through the iron and diamond lists, and if the player name is found in one of those lists, it will instantly return false. If it makes it through both lists without finding the player name, it will return true. You will need to do something similar to this for isIron and isDiamond as well.

If you also have a "groups.leather" then this can be done even more simply.

public boolean isLeather(String playerName) {
    for(String leatherPlayerName : getConfig().getStringList("groups.leather")) {
        if(leatherPlayerName.equals(playerName)) {
            return true;
        }
    }
    return false;
}

public boolean isIron(String playerName) {
    for(String ironPlayerName : getConfig().getStringList("groups.iron")) {
        if(ironPlayerName.equals(playerName)) {
            return true;
        }
    }
    return false;
}

public boolean isDiamond(String playerName) {
    for(String diamondPlayerName : getConfig().getStringList("groups.diamond")) {
        if(diamondPlayerName.equals(playerName)) {
            return true;
        }
    }
    return false;
}

This method would only search the respective list for leather/iron/diamond. Since you're calling all 3 methods in Stym anyway, this would be ideal.

Okay, that worked, thanks. Now, I don't get an error, but it isn't working properly. I alway get "This player is made out of leather!", even when the name is in the config.yml. Any idea? — Reum12, Nov 08 '15 at 22:02
@janErichsen this question is more suited to be on the minecraft or bukkit forums, not stack overflow. — EDToaster, Nov 08 '15 at 22:03
@JanErichsen I modified my answer to include my solution to the program always stating that the player is made of leather. — Calvin P., Nov 08 '15 at 22:24
Well, now I am confused. I understood the problem and fixed it, according to your very understandable answer. But it still doesn't work. — Reum12, Nov 08 '15 at 23:00
Hmm.. have to say I'm at a loss too then. I can't see where else it would evaluate incorrectly. Are you sure the strings are being entered correctly? using `.equals` will try to match the case, so if you don't have every capital/lowercase letter the same, it will not evaluate `true`. If this is the case, you could try `.equalsIgnoreCase` instead. — Calvin P., Nov 08 '15 at 23:07
I just found the mistake. It always asked for the group of "Krischon" (my Minecraft name), because I typed `sender.getName()` instead of `arguments[0]`. — Reum12, Nov 08 '15 at 23:19

Bukkit - NullPointerException

1 Answers1