public Discount(double minimum, double value, DiscountType typeFlag){
		if(minimum < 0) throw new IllegalArgumentException("Minimum purchase amount required cannot be negative.");
		if(value <= 0) throw new IllegalArgumentException("Discount value cannot be 0 or below.");
		if(value >= 1 && typeFlag == Discount.DiscountType.PERCENTAGE) throw new IllegalArgumentException("The percentage value cannot be 100% or above.");
		
		this.minimumPurchaseAmount = minimum;
		this.discountValue = value;	// discount value in fractions.
		this.typeFlag = typeFlag;
	}