[1.8.9] Item Holding

[Recable]

Okay so I've made this item where when help you can a player capability that makes it so you can't take damage (like in creative mode) and the potion effect weakness (so you all can't hurt people), but I've realised there's a problem because at the moment you must hold the gem  for the effect to work and when you switch to another item slot without holding the gem the effect goes, but if you hold the gem and then throw it out of your inventory it gives you the effects forever, how would I fix that?

 

package com.Recable.mod.gemstones;

import java.util.List;

import com.Recable.mod.MAGlobal;

import net.minecraft.enchantment.Enchantment;
import net.minecraft.enchantment.EnchantmentHelper;
import net.minecraft.entity.Entity;
import net.minecraft.entity.EntityLivingBase;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.entity.projectile.EntityArrow;
import net.minecraft.init.Items;
import net.minecraft.item.EnumAction;
import net.minecraft.item.Item;
import net.minecraft.item.Item.ToolMaterial;
import net.minecraft.item.ItemPickaxe;
import net.minecraft.item.ItemStack;
import net.minecraft.potion.Potion;
import net.minecraft.potion.PotionEffect;
import net.minecraft.stats.StatList;
import net.minecraft.world.World;

public class ModImmortalGemstone extends Item {

public ModImmortalGemstone(String unlocalizedName) {
	super();
	this.setUnlocalizedName(unlocalizedName);
	this.setCreativeTab(ModGlobal.modCreativeTabGemstones);
	this.setMaxStackSize(1);
}

@Override
public void onUpdate(ItemStack itemstack, World world, Entity entity, int i, boolean flag) {
     if (entity instanceof EntityPlayer) {          
    	 EntityPlayer Player = (EntityPlayer) entity;
          if(Player.getCurrentEquippedItem() != null && Player.getCurrentEquippedItem().getItem() instanceof ModImmortalGemstone) {
        	
        	  Player.capabilities.disableDamage = true;
        	  Player.addPotionEffect(new PotionEffect(Potion.weakness.id, 0, 100000 - 1));
          }
          else {
        	  Player.capabilities.disableDamage = false;
        	  Player.removePotionEffect(i);
          }
     }	 

}
}

[Draco18s]

If you throw an item into the world (but not into a chest (or other GUI) or itemframe) there is an OnEntityUpdate method.