"collection" is null

[maurxce]

I have a Database class which consists of the following code:

package me.lewd.poke.database;


import me.lewd.poke.Main;
import org.dizitart.no2.Nitrite;
import org.dizitart.no2.NitriteCollection;

public class Database {

    public Nitrite db;
    public NitriteCollection pokes;
    private String dataFolder = Main.instance.getDataFolder().getAbsolutePath();

    public void startDatabase() {
        db = Nitrite.builder()
                .filePath(dataFolder + "/data/pokes.db")
                .openOrCreate();

        pokes = db.getCollection("pokes");
    }

    public Nitrite getDatabase() { return db; }
    public NitriteCollection getCollection() { return pokes; }

    public void closeDatabase() {
        if (db.hasUnsavedChanges()) db.commit();
        if (!db.isClosed()) db.close();
    }
}

The startDatabase() method is called on start.
whenever I use the getCollection() method I get this error

java.lang.NullPointerException: Cannot invoke "org.dizitart.no2.NitriteCollection.find(org.dizitart.no2.Filter)" because "collection" is null

Using nitrite 3.4.4

[anidotnet]

Which version of JDK are you using? And please paste full stacktrace here.

[maurxce]

The code which is throwing the error

@EventHandler
public void onJoin(PlayerJoinEvent e) {
    Player player = e.getPlayer();
    NitriteCollection collection = new Database().getCollection();

    Filter filter = Filters.eq("target", player.getName());
    Cursor cursor = collection.find(filter);

    for (Document doc : cursor) {
        Object sender = doc.get("sender");
        player.sendMessage(sender.toString() + " poked you!");

        Filter removeFilter = Filters.and(
            Filters.eq("sender", sender.toString()),
            Filters.eq("target", player.getName())
        );
        collection.remove(removeFilter);
    }
}

Full error:

[13:55:37] [Server thread/ERROR]: Could not pass event PlayerJoinEvent to Poke v1.0-compiled
java.lang.NullPointerException: Cannot invoke "org.dizitart.no2.NitriteCollection.find(org.dizitart.no2.Filter)" because "collection" is null
	at me.lewd.poke.Main.onJoin(Main.java:94) ~[Poke-1.0-compiled.jar:?]
	at com.destroystokyo.paper.event.executor.asm.generated.GeneratedEventExecutor3.execute(Unknown Source) ~[?:?]
	at org.bukkit.plugin.EventExecutor.lambda$create$1(EventExecutor.java:75) ~[purpur-api-1.19.2-R0.1-SNAPSHOT.jar:?]
	at co.aikar.timings.TimedEventExecutor.execute(TimedEventExecutor.java:80) ~[purpur-api-1.19.2-R0.1-SNAPSHOT.jar:git-Purpur-1794]
	at org.bukkit.plugin.RegisteredListener.callEvent(RegisteredListener.java:70) ~[purpur-api-1.19.2-R0.1-SNAPSHOT.jar:?]
	at org.bukkit.plugin.SimplePluginManager.callEvent(SimplePluginManager.java:678) ~[purpur-api-1.19.2-R0.1-SNAPSHOT.jar:?]
	at net.minecraft.server.players.PlayerList.postChunkLoadJoin(PlayerList.java:372) ~[purpur-1.19.2.jar:git-Purpur-1794]
	at net.minecraft.server.players.PlayerList.lambda$placeNewPlayer$0(PlayerList.java:309) ~[purpur-1.19.2.jar:git-Purpur-1794]
	at net.minecraft.server.TickTask.run(TickTask.java:18) ~[purpur-1.19.2.jar:git-Purpur-1794]
	at net.minecraft.util.thread.BlockableEventLoop.doRunTask(BlockableEventLoop.java:153) ~[?:?]
	at net.minecraft.util.thread.ReentrantBlockableEventLoop.doRunTask(ReentrantBlockableEventLoop.java:24) ~[?:?]
	at net.minecraft.server.MinecraftServer.doRunTask(MinecraftServer.java:1368) ~[purpur-1.19.2.jar:git-Purpur-1794]
	at net.minecraft.server.MinecraftServer.d(MinecraftServer.java:185) ~[purpur-1.19.2.jar:git-Purpur-1794]
	at net.minecraft.util.thread.BlockableEventLoop.pollTask(BlockableEventLoop.java:126) ~[?:?]
	at net.minecraft.server.MinecraftServer.pollTaskInternal(MinecraftServer.java:1345) ~[purpur-1.19.2.jar:git-Purpur-1794]
	at net.minecraft.server.MinecraftServer.pollTask(MinecraftServer.java:1338) ~[purpur-1.19.2.jar:git-Purpur-1794]
	at net.minecraft.util.thread.BlockableEventLoop.managedBlock(BlockableEventLoop.java:136) ~[?:?]
	at net.minecraft.server.MinecraftServer.tickServer(MinecraftServer.java:1416) ~[purpur-1.19.2.jar:git-Purpur-1794]
	at net.minecraft.server.MinecraftServer.runServer(MinecraftServer.java:1194) ~[purpur-1.19.2.jar:git-Purpur-1794]
	at net.minecraft.server.MinecraftServer.lambda$spin$1(MinecraftServer.java:310) ~[purpur-1.19.2.jar:git-Purpur-1794]
	at java.lang.Thread.run(Thread.java:833) ~[?:?]

Using Eclipse Temurin 17.0.4 in IntelliJ

[anidotnet]

Why are you calling new Database().getCollection();. You should have called startDatabase() before you call getCollection() on it.

[maurxce]

the startDatabase() method is being called on start immediately, do I have to call it every time I want to access my collection?

[anidotnet]

Whenever you create a new instance of Database by calling new Database(), you have to call startDatabase() on it, otherwise all variables inside Database will be null. It has nothing to do with nitrite, it is basic java.

[maurxce]

My mistake, sorry.
The problem is solved now, I appreaciate your help