private void applyDiscount()
	{
		isQuantum= false;
		try
		{
			if(!regularDiscount.isSelected() && !quantumDiscount.isSelected())
				this.shop.setDiscountStrategy(new NoDiscount());
			if(regularDiscount.isSelected())
				this.shop.setDiscountStrategy(new RegularCustomerDiscount());
			if(quantumDiscount.isSelected())
			{
				this.shop.setDiscountStrategy(new QuantumDiscount());
				isQuantum = true;
			}
			if(quantumDiscount.isSelected() && regularDiscount.isSelected())
				throw new IllegalArgumentException("You are not allowed to select 2 discounts at the same time.");
		}
		catch(IllegalArgumentException e)
		{
			JOptionPane.showMessageDialog(null, e.getMessage(), 
					 "Error", JOptionPane.ERROR_MESSAGE); 
		}
	}