Intro JAVA class very basic understanding and basic functions I was hoping to see this layed out as I'd liek to write each line one at a time and focus on understanding it line by line. I've been trying to use the comment function to leave myself reminders and notes in hope that I can remember what a line of code does.

a. (Invoice Class) Create a class called Invoice that a hardware store might use to represent an invoice for an item sold at the store.

b. An Invoice should include four pieces of information as instance variablesa part number (type String), a part description (type String), a quantity of the item being purchased (type int) and a price per item (double).

c. Your class should have a constructor that initializes the four instance variables. Provide a set and a get method for each instance variable.

d. In addition, provide a method named getInvoiceAmount that calculates the invoice amount (i.e., multiplies the quantity by the price per item), then returns the amount as a double value. If the quantity is not positive, it should be set to 0. If the price per item is not positive, it should be set to 0.0.

e. Write a test app named InvoiceTest that demonstrates class Invoices capabilities.