Callbacks in Java

Callback.java

public abstract class Callback<T>
{
    public abstract void execute(T result);
    
    public final void call(Plugin plugin, T result)
    {
        if(Bukkit.isPrimaryThread())
        {
            this.execute(result);
            return;
        }
        new BukkitRunnable()
        {
            @Override
            public void run()
            {
                Callback.this.execute(result);
            }
        }.runTask(plugin);
    }
}