Minecraft Plugin

別のクラスからコマンドを読み込ませたいのですが動きません
Error Code:

[16:10:46 INFO]: [test_plugin] Enabling test_plugin v0.0.1
[16:10:46 ERROR]: Error occurred while enabling test_plugin v0.0.1 (Is it up to date?)
java.lang.IllegalArgumentException: Plugin already initialized!
        at org.bukkit.plugin.java.PluginClassLoader.initialize(PluginClassLoader.java:183) ~[spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.plugin.java.JavaPlugin.<init>(JavaPlugin.java:60) ~[spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at grass.command.Grass_Command.<init>(Grass_Command.java:13) ~[?:?]
        at grass.plugin.Grass.onEnable(Grass.java:16) ~[?:?]
        at org.bukkit.plugin.java.JavaPlugin.setEnabled(JavaPlugin.java:264) ~[spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.plugin.java.JavaPluginLoader.enablePlugin(JavaPluginLoader.java:337) [spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.plugin.SimplePluginManager.enablePlugin(SimplePluginManager.java:403) [spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.craftbukkit.v1_12_R1.CraftServer.enablePlugin(CraftServer.java:381) [spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.craftbukkit.v1_12_R1.CraftServer.enablePlugins(CraftServer.java:330) [spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at net.minecraft.server.v1_12_R1.MinecraftServer.t(MinecraftServer.java:422) [spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at net.minecraft.server.v1_12_R1.MinecraftServer.l(MinecraftServer.java:383) [spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at net.minecraft.server.v1_12_R1.MinecraftServer.a(MinecraftServer.java:338) [spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at net.minecraft.server.v1_12_R1.DedicatedServer.init(DedicatedServer.java:272) [spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at net.minecraft.server.v1_12_R1.MinecraftServer.run(MinecraftServer.java:545) [spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at java.lang.Thread.run(Unknown Source) [?:1.8.0_191]
Caused by: java.lang.IllegalStateException: Initial initialization
        at org.bukkit.plugin.java.PluginClassLoader.initialize(PluginClassLoader.java:186) ~[spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.plugin.java.JavaPlugin.<init>(JavaPlugin.java:60) ~[spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at grass.plugin.Grass.<init>(Grass.java:12) ~[?:?]
        at sun.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method) ~[?:1.8.0_191]
        at sun.reflect.NativeConstructorAccessorImpl.newInstance(Unknown Source) ~[?:1.8.0_191]
        at sun.reflect.DelegatingConstructorAccessorImpl.newInstance(Unknown Source) ~[?:1.8.0_191]
        at java.lang.reflect.Constructor.newInstance(Unknown Source) ~[?:1.8.0_191]
        at java.lang.Class.newInstance(Unknown Source) ~[?:1.8.0_191]
        at org.bukkit.plugin.java.PluginClassLoader.<init>(PluginClassLoader.java:90) ~[spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.plugin.java.JavaPluginLoader.loadPlugin(JavaPluginLoader.java:129) ~[spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.plugin.SimplePluginManager.loadPlugin(SimplePluginManager.java:327) ~[spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.plugin.SimplePluginManager.loadPlugins(SimplePluginManager.java:248) ~[spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at org.bukkit.craftbukkit.v1_12_R1.CraftServer.loadPlugins(CraftServer.java:305) ~[spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        at net.minecraft.server.v1_12_R1.DedicatedServer.init(DedicatedServer.java:205) ~[spigot-1.12.2.jar:git-Spigot-79a30d7-acbc348]
        ... 2 more

Code [Main]:

package grass.plugin;

import java.util.Collection;

import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.entity.Player;
import org.bukkit.plugin.java.JavaPlugin;

import grass.command.Grass_Command;

  public class Grass extends JavaPlugin {

      @Override
      public void onEnable() {
          Grass_Command commands = new Grass_Command(this);
          getCommand("save").setExecutor(commands);
      }

    @Override
      public boolean onCommand(CommandSender sender, Command command, String label, String[] args) {
            if (command.getName().equalsIgnoreCase("kickall")) {
                Collection<? extends Player> players = getServer().getOnlinePlayers();
                  for(Player player:players){
                   player.kickPlayer("Kicked");
                    }
              }
              return true;
           }

      @Override
      public void onDisable() {
          System.out.println("プラグインが無効になりました");
      }
  }

Code [Command Class]:

package grass.command;

import org.bukkit.Bukkit;
import org.bukkit.World;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.plugin.java.JavaPlugin;

import grass.plugin.Grass;

public class Grass_Command extends JavaPlugin {

    public Grass_Command(Grass grass) {
        // TODO 自動生成されたコンストラクター・スタブ
    }

    @Override
    public boolean onCommand(CommandSender sender, Command cmd, String label, String[] args) {
            if (cmd.getName().equalsIgnoreCase("save")) {
                sender.sendMessage("セーブしています...");
                for(World worlds: Bukkit.getWorlds()) {
                    worlds.save();
                }
            }
            return false;

    }
  }