Development Assistance Firework arrows problem does not extend JavaPlugin..

Hello,

I just started programming and i'm having some issue's with my code.
I now have this code:

Code:

import net.minecraft.server.v1_8_R1.EntityFireworks;
import net.minecraft.server.v1_8_R1.PacketPlayOutEntityStatus;
import net.minecraft.server.v1_8_R1.World;

import org.bukkit.Color;
import org.bukkit.FireworkEffect;
import org.bukkit.Location;
import org.bukkit.craftbukkit.v1_8_R1.CraftWorld;
import org.bukkit.craftbukkit.v1_8_R1.entity.CraftPlayer;
import org.bukkit.entity.Firework;
import org.bukkit.entity.Player;
import org.bukkit.entity.Projectile;
import org.bukkit.event.entity.ProjectileHitEvent;
import org.bukkit.inventory.meta.FireworkMeta;

public class FirstPlugin extends EntityFireworks {
    Player[] players = null;

    public FirstPlugin(World world, Player... p) {
        super(world);
        players = p;
        this.a(0.25F, 0.25F);
    }

    boolean gone = false;

    @Override
    public void s_() {
        if (gone) {
            return;
        }

        if (!this.world.isStatic) {
            gone = true;

            if (players != null)
                if (players.length > 0)
                    for (Player player : players)
                        (((CraftPlayer) player).getHandle()).playerConnection.sendPacket(new PacketPlayOutEntityStatus(this, (byte) 17));
                else
                    world.broadcastEntityEffect(this, (byte) 17);
            this.die();
        }
    }

    public static void spawn(Location location, FireworkEffect effect, Player... players) {
        try {
            FirstPlugin firework = new FirstPlugin(((CraftWorld) location.getWorld()).getHandle(), players);
            FireworkMeta meta = ((Firework) firework.getBukkitEntity()).getFireworkMeta();
            meta.addEffect(effect);
            ((Firework) firework.getBukkitEntity()).setFireworkMeta(meta);
            firework.setPosition(location.getX(), location.getY(), location.getZ());

            if ((((CraftWorld) location.getWorld()).getHandle()).addEntity(firework)) {
                firework.setInvisible(true);
            }
        } catch (Exception e) {
            e.printStackTrace();
        }
    }
public void onHit(ProjectileHitEvent e){
    Projectile p = e.getEntity(); //Getting the projectile
    FireworkEffect.Builder builder = FireworkEffect.builder();
    FireworkEffect effect = builder.flicker(false).trail(false).with(FireworkEffect.Type.BALL).withColor(Color.RED).withFade(Color.BLUE).build(); //Build the firework to suit your liking
    FirstPlugin.spawn(p.getLocation(), effect); //Spawning the firework
}
}

and im getting this error:

Code:

[15-03 18:19:30 ] [Server] ERROR Could not load 'plugins/FirstPlugin.jar' in folder 'plugins'
[15-03 18:19:30 ] [Server] [Informatie] org.bukkit.plugin.InvalidPluginException: main class `me.MaestroSwagger.firstplugin.FirstPlugin' does not extend JavaPlugin
[15-03 18:19:30 ] [Server] [Informatie] at org.bukkit.plugin.java.PluginClassLoader.<init>(PluginClassLoader.java:73) ~[spigot1.8.new.jar:git-Spigot-bf0ac55-3ee97a3]
[15-03 18:19:30 ] [Server] [Informatie] at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:131) ~[spigot1.8.new.jar:git-Spigot-bf0ac55-3ee97a3]
[15-03 18:19:30 ] [Server] [Informatie] at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:329) ~[spigot1.8.new.jar:git-Spigot-bf0ac55-3ee97a3]
[15-03 18:19:30 ] [Server] [Informatie] at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:251) [spigot1.8.new.jar:git-Spigot-bf0ac55-3ee97a3]
[15-03 18:19:30 ] [Server] [Informatie] at org.bukkit.craftbukkit.v1_8_R1.CraftServer.loadPlugins(CraftServer.java:291) [spigot1.8.new.jar:git-Spigot-bf0ac55-3ee97a3]
[15-03 18:19:30 ] [Server] [Informatie] at net.minecraft.server.v1_8_R1.DedicatedServer.init(DedicatedServer.java:152) [spigot1.8.new.jar:git-Spigot-bf0ac55-3ee97a3]
[15-03 18:19:30 ] [Server] [Informatie] at net.minecraft.server.v1_8_R1.MinecraftServer.run(MinecraftServer.java:505) [spigot1.8.new.jar:git-Spigot-bf0ac55-3ee97a3]
[15-03 18:19:30 ] [Server] [Informatie] at java.lang.Thread.run(Thread.java:722) [?:1.7.0_21]
[15-03 18:19:30 ] [Server] [Informatie] Caused by: java.lang.ClassCastException: class me.MaestroSwagger.firstplugin.FirstPlugin
[15-03 18:19:30 ] [Server] [Informatie] at java.lang.Class.asSubclass(Class.java:3046) ~[?:1.7.0_21]
[15-03 18:19:30 ] [Server] [Informatie] at org.bukkit.plugin.java.PluginClassLoader.<init>(PluginClassLoader.java:71) ~[spigot1.8.new.jar:git-Spigot-bf0ac55-3ee97a3]
[15-03 18:19:30 ] [Server] [Informatie] ... 7 more

I dont know how to fix this can somebody help me?
sorry if this is a stupid question i just started programming!
Thanks in advance!