java.lang.IllegalArgumentException: Plugin already initialized. What's going on?

Question

When I\'m testing my new plugin an exception keeps getting thrown: java.lang.IllegalArgumentException: Plugin already initialized! Please help! Here\'s the code:

Answer 1

The stacktrace clearly tells where is the problem. What is a stack trace, and how can I use it to debug my application errors?
The error:

java.lang.IllegalArgumentException: Plugin already initialized!
...
Caused by: java.lang.IllegalStateException: Initial initialization
...
at me.plugin.example.Main.<init>(Main.java:19) ~[?:?]

Your code:

@Override
public void onEnable() {
    getServer().getPluginManager().registerEvents(new Main(), this);
} //<-- 19th line

And the problem is when you register your event you are creating a new instance of your Main class. So replace new Main()

getServer().getPluginManager().registerEvents(new Main(), this);

with this

getServer().getPluginManager().registerEvents(this, this);

Answer 2

I would really recommend you to put your event handler in a separate class.

Try removing the below line

getServer().getPluginManager().registerEvents(new Main(), this);

and please don't ask your question several times.

Answer 3

PluginAlreadyInitialized error occours when the .jar file contains more than one subclass of JavaPlugin class. Use the JavaPlugin class only once in all plugins from.