Thread: URGENT! Why won't my addToInvoice method work?

Hey guys,
I'm working on arrays and I'm just not getting the hang of it. Every time my addToInvoice method is called and printed, it's not coming out correctly. Here's what the output is supposed to look like when you choose option 1 or 3.
This line serves customers with 5 or fewer items
------------------------------------------------

1. Buy an item
2. Modify the quantity of an item
3. Show the items purchased so far
4. Done

Your choice:
1
Enter the product name: Walnuts
Enter the price: 9.99
How many of Walnuts did you buy? Please enter the quantity: 2

1. Buy an item
2. Modify the quantity of an item
3. Show the items purchased so far
4. Done

Your choice:
3
Product: Walnuts Price: $9.99 Quantity: 2
Product: 1% Milk Price: $1.99 Quantity: 2
Running Total: $23.96

And here is what my output is giving me:
1
Enter the product name: milk
Enter the price: 2.99
How many of milk did you buy? Please enter the quantity: 2
1. Buy an item
2. Modify the quantity of an item
3. Show the items purchased so far
4. Done

Your choice:
1
Enter the product name: soup
Enter the price: 1.99
How many of soup did you buy? Please enter the quantity: 1
1. Buy an item
2. Modify the quantity of an item
3. Show the items purchased so far
4. Done

Your choice:
1
Enter the product name: sauce
Enter the price: 2.39
How many of sauce did you buy? Please enter the quantity: 1
1. Buy an item
2. Modify the quantity of an item
3. Show the items purchased so far
4. Done

Your choice:
3
null

null

Produt: Product: sauce Price: $2.39 Price: 0.0 Quantity: 1

null

null

Here is my product class:

public class Product   {
    private String name;
    private double price;
 
 
    public Product(String name, double price) {
        this.name = name;
        this.price = price;
    }
 
 
    public void setName(String name)   {
        this.name = name;
    }
 
 
    public String getName()  {
        return name;
    }
 
 
    public void setPrice(double price)  {
        this.price = price;
    }
 
 
    public double getPrice()  {
        return price;
    }
 
 
    public String toString()  {
        NumberFormat n = NumberFormat.getCurrencyInstance(Locale.US);
        return "Product: " + name + "\tPrice: " + n.format(price);
    }
}

And my LineItem class:

public class LineItem
{
    private Product p;
    private int quantity;
    private double amountOwed;
    private int q;
    private double price;
    public LineItem(Product p, int quantity) {
        this.p=p;
        this.quantity=quantity;
    }
 
    public double getAmount() {
        return quantity*price;
    }
 
    public void setQuantity(int q) {
        this.q=q;
    }
 
    public int getQuantity() {
        return quantity;
    }
 
    public Product getProduct() {
        return p;
    }
 
    public java.lang.String toString() {
        return "Produt: " + p + "\tPrice: " + price + "\tQuantity: " + quantity + " ";
    }
}

And my invoice method:

public class Invoice
{
    private LineItem[] collection;
    private int numItems;
    private double runningTotal=0;
    private double price;
    private int quantity;
 
    public Invoice() {
        numItems=0;
    }
 
    public void addToInvoice(LineItem item) {
        collection=new LineItem[5];
        collection[numItems]=item;
        numItems++;
    }
 
    public int getNumItems() {
        return numItems;
    }
 
    public double getRunningTotal() {
        return runningTotal;
    }
 
    public void print() {
        for (int i=0; i<5; i++) {
        System.out.println(collection[i] + "\n");
        runningTotal = runningTotal + price*quantity;
       }
       getRunningTotal();
    }
 
    public void update(java.lang.String name, int quantity) {
 
    }
}

AND FINALLY my main method:

public class Cashier   {
    public static void main(String args[]) { 
        final int MAXITEMS = 5;
        Scanner keyboard = new Scanner(System.in);
        NumberFormat n = NumberFormat.getCurrencyInstance(Locale.US); 
        System.out.println("Welcome to CS 140 Store Express Line");
        System.out.println("This line serves customers with " + MAXITEMS + " or fewer items");
        System.out.println("------------------------------------------------\n");
 
        Invoice invoice = new Invoice();
        do {
            System.out.println("\t1. Buy an item");
            System.out.println("\t2. Modify the quantity of an item");
            System.out.println("\t3. Show the items purchased so far");
            System.out.println("\t4. Done");
            System.out.println("\nYour choice: ");
            int choice = Integer.parseInt(keyboard.nextLine());
            switch(choice) {
                case 1:
                   if (invoice.getNumItems() < MAXITEMS) {
                       System.out.print("Enter the product name: ");
                       String name = keyboard.nextLine();
 
                       System.out.print("Enter the price: ");
                       double price = Double.parseDouble(keyboard.nextLine() );
 
                       System.out.print("How many of " + name + " did you buy? Please enter the quantity: ");
                       int quantity = Integer.parseInt(keyboard.nextLine() );
                       LineItem item = new LineItem(new Product(name, price), quantity);
                       invoice.addToInvoice(item);
                   }
                   else
                       System.out.println("This line is customers for <= " + MAXITEMS + " items only");
                   break;
 
                case 2:
                   System.out.println("Enter the name of the product");
                   String name = keyboard.nextLine();
                   System.out.println("Enter the new quantity: ");
                   int quantity = Integer.parseInt(keyboard.nextLine() );
                   invoice.update(name, quantity);
                   break;
 
                case 3:
                   invoice.print();
                   break;
 
                case 4:
                   System.out.println("Thanks for using CS 140 store");
                   System.out.println("Here is your invoice information");
                   System.out.println("--------------------------------");
                   invoice.print();
                   System.out.println("\nPlease come back again.  Have a nice day!");
                   System.exit(0);
 
                default:
                   System.out.println("Wrong choice.  Choose a valid option");
            }    // end of switch 
        }  while (true);  // end of do - while loop
    }     // end of main method
}   // end of Cashier class

can anyone tell me what I'm doing wrong?

The println() statement is printing the collection at all 5 positions. The last 3 positions have nothing in them so I think that's why I'm getting null. I don't know if I declared the array correctly within the addToInvoice method because the output should only print positions in the collection that have something in them. But I don't know why the first position is printing null, and why Product: prints twice and Price: prints twice.

Okay so for the last 3 spots giving null, I changed my method's for loop to only print as many items as I have put in by switching my code to

    public void print() {
        for (int i=0; i<numItems; i++) {
        System.out.println(collection[i] + "\n");
        runningTotal = runningTotal + price*quantity;
       }
       System.out.println(getRunningTotal());
    }

So now I'm just getting after adding only two products (milk & butter):
1. Buy an item
2. Modify the quantity of an item
3. Show the items purchased so far
4. Done

Your choice:
3
null

Produt: Product: Butter Price: $1.29 Price: 0.0 Quantity: 1

0.0


But I don't know why I'm getting null for the first position and why product and price are printing twice.

The first position in the collection is giving me the null value.

I'm sorry, I don't quite understand everything in Java programming enough to figure out without a general example, and just telling me I'm missing an import statement does not really help me. This is my first class for programming and unfortunately I had no choice but to take it online. I don't learn well that way. But I had to take the class or I will lose my commission as an officer in the Navy. That being said, the textbook that was given for the class has about 4 pages for chapter and is pretty much useless so I'm stuck trying to figure this out on my own. I really appreciate your help so far but will all due respect sir, I am swallowing my pride and asking you if you could dumb it down for me. I'm trying my best to finish this by tomorrow night.

The only import statements I was given to use are

import java.text.*;     // for NumberFormat
import java.util.*;     // for Locale

in the product class and

import java.util.Scanner;
import java.text.*;      // for the NumberFormat 
import java.util.*;

in the main method Cashier. Sorry I didn't realize I didn't paste them/[COLOR="Silver"]

--- Update ---

[/COLOR]I think the reason it is skipping position zero has something to do with this method:

    public void addToInvoice(LineItem item) {
        collection=new LineItem[5];
        collection[numItems]=item;
        numItems++;
    }

but I thought when I wrote collection[numItems]=item; it was telling the compiler to put the first product in position 0 since numItems was initialized to zero. So I'm not sure why it is skipping.

--- Update ---

The response 1 means you're telling the system you're buying another product. So it asks for the product name, price and quantity. Then prompts you again. If you want to buy another item you enter 1 again. Entering 3 gets the program to give you a list of what you have bought so far and tells you the name, price, and quantity of each as well as the running total of the entire invoice at the end.

Oh I see what you mean about not having an active console. It looks like to me yours output is right.. Could you guide me on what to do next?

--- Update ---

Okay I tried only doing one product too and mine worked other than posting the product and price twice like before. Why is it that when I add a second product the first becomes null?

I realized by creating the collection in addToInvoice was creating a new collection every time addToInvoice is called. So I updated these two methods to:

    public Invoice() {
        collection=new LineItem[5];
        numItems=0;
    }
 
    public void addToInvoice(LineItem item) {
        collection[numItems]=item;
        numItems++;
    }

and I got (after adding two products milk & butter):
1. Buy an item
2. Modify the quantity of an item
3. Show the items purchased so far
4. Done

Your choice:
3
Produt: Product: Milk Price: $2.99 Price: 0.0 Quantity: 1

Produt: Product: Butter Price: $1.99 Price: 0.0 Quantity: 2

0.0

So we're getting there, thank you very much. I think the next thing I need to clear is the double print of product: and price: I purposely misspelled Product: from the LineItem class so I could figure out which is which. But I'm still unclear of why it's being printed twice.

So p's toString() is being called and I'm assuming that's the one I want to print. But I think the toString is being printed from LineItem too... I was instructed to create a toString for LineItem to "Return a string representation of this line item " but I don't understand what for, because it looks like the product toString and the LineItem toString share the same attributes. Should I get rid of the LineItem toString?

Thank you very much sir, I was able to figure it out. The final thing I need to do is write the method for public void update(java.lang.String name, int quantity) but I think I can do it. I appreciate the help. Have a good night.