NullPointerExcept for no apparent reason

Question

I am working on developing a Bukkit plugin (the error is not related to bukkit or it's api, but I included the fact that I am using it for completeness, if you do not know what it is/haven't heared of it you should still be able to answer this question). The plugin I am working on is an anti chat spam plugin. I am getting a nullpointerexception for no apparent reason. Here is some code:

public class SpamListener implements Listener{
private HashMap<String, Long> lastMessage;
private HashMap<String, Integer> spamScore;

public void init(){
    lastMessage = new HashMap<String, Long>();
    spamScore = new HashMap<String, Integer>(); 
}

@EventHandler
public void playerChatEvent(AsyncPlayerChatEvent e){
    if(AntiGrief.instance.config.getBoolean("antispam.enabled") && (!e.getPlayer().hasPermission("antigrief.spam.bypass"))){
        Player player = e.getPlayer();
        String name = player.getName();
        int startingScore = spamScore.get(name); // <-- NullPointerException occurs here

        //More spam checking code here

    }
}

JavaPlugin class (main class, for those not familiar with bukkit):

    spamListener = new SpamListener();
    spamListener.init(); // <-- yes the method is being called, same error occurs if the hashmap is instantiated in the constructor and declaration
    pm.registerEvents(spamListener, instance);

Stacktrace: http://pastebin.com/cciibpXp

Thanks in advance for any answers :)

Answer 1

I suspect the problem isn't spamScore being null - it's the value in the map being null, because you haven't populated the map. You're then trying to unbox that null reference to an int, and that fails. So think of your code like this:

Integer startingScoreReference = spamScore.get(name);
int startingScore = startingScoreReference.intValue();

Now obviously if startingScoreReference is null (which it will be if there's no entry for name in your map) then the second line will cause a NullPointerException.

So basically you need to either ensure that your map will always contain an entry for name, or you need to handle the case where there's no such entry. For example, you might want:

Integer mapValue = spamScore.get(name);
int startingScore = mapValue == null ? 0 : mapValue.intValue();

(The intValue() call could be a cast to int instead, depending on your preference.)