Make an Invoice class that might serve as a receipt for items sold. An Invoice should be defined by the following attributes:
- productName : String
- quantityPurchased : int
- pricePerItem : double
Provide getters and setters for each attribute, making sure that the numeric values given are not negative. Set them to 0 if they are. Include a method that calculates the invoice amount (i.e., multiplies the quantity by the price per item), then returns the amount as a double value. Make a test program that shows everything working.