A java array of objects

Question

I have an assignment where I have to create three classes, a client class that performs all I/O, a catalog class that maintains a list of catalogItem objects and a catalogItem class that defines a single item in the store's catalog.

I'm trying to start simple at first and create the array and make sure that it is accepting data before I move on to the rest of the assignment. I was able to compile it with no issues but when I am trying to display the array, I get nothing.

import java.util.Scanner;

public class lab3
{
    public static void main(String args[])
    {
        Scanner in = new Scanner(System.in);

        Catalog catalog = new Catalog();

        boolean endCatalog = false;
        while (!endCatalog)
        {
            System.out.println("Please choose and option: \n"
            + "1 - Display all items of the catalog\n"
            + "2 - Display an item by keyword\n"
            + "3 - Add an item to the catalog\n"
            + "4 - Remove an item from the catalog\n"
            + "5 - Change the cost of one item in the catalog\n"
            + "6 - Change the cost of all items in catalog by percent\n"
            + "7 - Exit");

            int choice = in.nextInt();

            switch (choice) {
            case 1: System.out.println(catalog.displayAll()); break;
            case 2: System.out.println("Display keyword"); break;
            case 3: System.out.println("Add item:\nEnter ID: ");
                        int newId=in.nextInt();
                        System.out.println("Enter description: ");
                        String newDesc=in.next();
                        System.out.println("Enter cost: ");
                        double newCost=in.nextDouble();
                        catalog.add(newId, newDesc, newCost); break;
            case 4: System.out.println("Remove item"); break;
            case 5: System.out.println("Change cost of one item"); break;
            case 6: System.out.println("Change cost by %"); break;
            case 7: endCatalog=true; break; }

        }   
    }
}


class Catalog
{
    final static int MAX = 100;
    private CatalogItem[] catalogItems;
    int inUse;

    public Catalog()
    {
        catalogItems=new CatalogItem[MAX]; 
    }   
    public void add(CatalogItem newItem)
    {
        inUse = 0;
        if(inUse<MAX) {
            catalogItems[inUse] = newItem;
            inUse++; }
    }
    public void add(int newId, String newDesc, double newCost)
    {
        CatalogItem newItem = new CatalogItem(newId, newDesc, newCost);

    }
    /*public void remove(int id)
    {

    }
    public String find(String keyword)
    {

    }
    public void changeCost(int id, double percent)
    {

    }
    public void increaseCost(double percent)
    {

    }
    public String toString()
    {
    }
    public boolean equals(Catalog obj)
    {

    }*/ 

    public String displayAll()
    {
        String str = "";

        for (int i=0; i<inUse; i++) {
            str = str + "\n" + catalogItems[i]; }

        return str;
    }   
}



class CatalogItem
{
    private int itemID;
    private String description;
    private double cost;

    public CatalogItem()
    {
        itemID = 1;
        description = " ";
        cost = 0.0;
    }

    public CatalogItem(int newID, String newDesc, double newCost)
    {
        itemID = newID;
        description = newDesc;
        cost = newCost;
    }

    public int getItemID()
    {
        return itemID;
    }

    public void setItemID(int newID)
    {
        itemID=newID;
    }

    public String getDescription()
    {
        return description;
    }

    public void setDescription(String newDesc)
    {
        description=newDesc;
    }

    public double getCost()
    {
        return cost;
    }

    public void setCost(double newCost)
    {
        cost=newCost;
    }

    public String toString()
    {
        return itemID + ", " + description + ", " + cost;
    }

    public boolean equals(CatalogItem obj)
    {
        return false;
    }
}

Answer 1

There is not items ever added to:

private CatalogItem[] catalogItems;

That is so, because you call only this method:

public void add(int newId, String newDesc, double newCost)
{
    CatalogItem newItem = new CatalogItem(newId, newDesc, newCost);

}

And that one will never call method that actually tries to add something to the array:

   public void add(CatalogItem newItem)
    {
        inUse = 0;
        if(inUse<MAX) {
            catalogItems[inUse] = newItem;
            inUse++; }
    }

In the long run that method will also not work, because item is always added to the index 0. That is so, because as first thing you always set: inUse = 0.

Answer 2

You call this method to add the catalog item:

public void add(int newId, String newDesc, double newCost)
{
    CatalogItem newItem = new CatalogItem(newId, newDesc, newCost);

}

But as we can see, this doesn't actually do anything with the object it creates. Did you mean to have this overload of add() call the other one? That would be a good design.

Also, in the other version of add(), you do this:

    inUse = 0;

Since you reset inUse every time add() is called, your array will never contain more than one item. Do you see why this is? You should just take this line out.

Answer 3

Here's the problem:

public void add(int newId, String newDesc, double newCost)
{
    CatalogItem newItem = new CatalogItem(newId, newDesc, newCost);

}

What happens to newItem after it is created?