I'm creating a balance for an item, and everytime you add money to that balance, the balance variable goes up. But the problem is that the balance is the same for all the items. So if I added $100 to an item, it would add to everybody elses items aswell. I hope I explained it right

You need to store any data about Items in the ItemStack. You can't store it in the Item class as there is only ever one instance of it.

 

How would I do this?

Every ItemStack has an NBTTagCompound associated with it (ItemStack#stackTagCompound). You can store any data you want there.

 

Ok, so I already have it set-up with NBT, but it is the same on all the items, what am I doing wrong

package com.bugzoo.FinancialMod;

import java.util.List;

import net.minecraft.entity.Entity;
import net.minecraft.entity.player.EntityPlayer;
import net.minecraft.item.Item;
import net.minecraft.item.ItemStack;
import net.minecraft.nbt.NBTTagCompound;
import net.minecraft.util.ChatComponentText;
import net.minecraft.util.EnumChatFormatting;
import net.minecraft.world.World;

public class ItemDebitCard extends Item {
	public ItemDebitCard(){
		setMaxStackSize(1);
		setUnlocalizedName("DebitCard");
		setCreativeTab(FinancialMod.financialTab);
	}

	int UniquePin = 1000 + (int)(Math.random()*9999); 
	public static double balance;

	    @Override
	    public void onCreated(ItemStack itemStack, World world, EntityPlayer player) {
	    	 itemStack.stackTagCompound = new NBTTagCompound();
	    	 itemStack.stackTagCompound.setString("owner", player.getDisplayName());
	    	 itemStack.stackTagCompound.setInteger("pin", UniquePin);
	    	 itemStack.stackTagCompound.setDouble("balance", balance);
	    	 if(!world.isRemote){
	    	 player.addChatComponentMessage(new ChatComponentText(EnumChatFormatting.RED + "Your Unique Pin is " + UniquePin));
	    	 }
	    }

	    public void addInformation(ItemStack itemStack, EntityPlayer player, List list, boolean par4) {
	    	 if (itemStack.stackTagCompound != null) {
                     String owner = itemStack.stackTagCompound.getString("owner");
                     String pin = itemStack.stackTagCompound.getString("pin");
                     list.add("Owner: " + owner);
                     list.add("Balance: " + balance);
                     
                     
                     if (!owner.equals(player.getDisplayName())) {
                    	  list.add("Pin: " + EnumChatFormatting.OBFUSCATED + pin);
    		    	 } else {
    		    		 list.add("Pin: " + pin);
    		    	 }
	    	 }
	    	 
             }
	    
	    
	    }