我正在编写一个模拟商店的程序。问题是，当我尝试获取总数时，它只给出了我购买的最后一件物品的总数，而不是购买的所有物品的总数。我做错了什么，我能解决什么？
import java.util.Scanner;
public class Invoice {
public static String partNum;
public String description;
public int quantity;
public double price;
public String part_description(String parts){
partNum=parts;
if(parts.equals("10")){
description="This is a large metal hammer, $20";price=20;}
else if(parts.equals("15")){description="This is a small plastic hammer, $5";price= 5;}
else if(parts.equals("20")){description="This is a medium wooden hammer, $10";price=10;}
else if(parts.equals("25")){description="This is a bucket of paint, $25";price=25;}
else{description="No such part number exists.";}
return description;
}
public void setquantity(int amount){
quantity=amount;
}
public int getquantity(){
return quantity;
}
public void setprice(double cost){
price=cost;
if(cost<0){cost=0;}
}
public double getprice(){
return price;
}
public double getInvoiceAmount(double total){
total=total+(quantity*price);
return total;
}
public static void main(String[] args){
Scanner s1= new Scanner(System.in);
Invoice invoiceObject= new Invoice();
boolean ask=true;
while(ask==true){
System.out.println("Chose one of the fallowing part numbers: 10, 15, 20, 25");
partNum=s1.nextLine();
System.out.println(invoiceObject.part_description(partNum));
System.out.printf("\nHow many #%s would you like to get: ", partNum);
int numOf=s1.nextInt();
invoiceObject.setquantity(numOf);
System.out.println("would you like to keep shopping? chose true or false");
ask=s1.nextBoolean();
partNum=s1.nextLine();
}
System.out.println("Your total price will be:$ "+invoiceObject.getInvoiceAmount(0));
}}