Invoice Program - Convert Strings For Quantity And Price To Numeric Types

In the test program, you will need to convert the Strings for quantity and price to numeric types. To do this, you could use the Integer.parseInt() method and the Double.parseDouble() methods. I'm not sure what he means by that. I attempted it in my program but I get these errors

Exception in thread "main" java.lang.Error: Unresolved compilation problems:
number cannot be resolved to a variable
description cannot be resolved to a variable
quantity cannot be resolved to a variable
price cannot be resolved to a variable
Duplicate local variable quantity
Duplicate local variable price
Syntax error on token "myInvoice", delete this token
The method getinvoiceAmount() is undefined for the type String

at InvoiceTest.main(InvoiceTest.java:7)

Code:
 
public class Invoice
{
private String number; //Instance variables
private String description;//Instance variables
private int quantity;//Instance variables
private double price;//Instance variables
 
 [Code] .....