Getting data from another class in Java

Question

public class Item {

    /**
    * Instance variables for this class
    */

    private String itemName;
    private int itemQuantity;

    /**
    * Contructor for this class
    */

    public Item (String itemName, int itemQuantity) {
        this.itemName = itemName;
        this.itemQuantity = itemQuantity;
    }
    //setter and getter methods
    public String getItemName () { 
        return itemName;
    }
    public void setItemName(String itemName) {
        this.itemName = itemName;
    }

    public int getItemQuantity () {
        return itemQuantity;
    }
    public void setItemQuantity(int itemQuantity) {
        this.itemQuantity = itemQuantity;
    }
}

Ok..I already have the class for item. Now I have to write the CartItem class. The description that was given are as follows:

class CartItem{ 
/*
Objects of this class are used to hold items that the shopper purchases in the super market. 
There are two attributes in this class, an item (an object created from the Item class) and a quantity (the number of that item that the shopper purchases). You have to write these two attributes. Note that one of the two will have a user defined data type. 
*/

}

public class CartItem {
    private Item item; //item from the item class
    private int itemQuantity; //quantity how much shopper buys

    public CartItem(Item itemName, int itemQuantity) {
        this.getItem();
        this.getQuantity();
    }


    public Item getItem() {
        return item;
    }
    public void setItem(Item item) {
        this.item = item;
    }

    public int getQuantity() {
        return itemQuantity;
    }
    public void setQuantity(int quantity) {
        this.itemQuantity = itemQuantity;
    }
}

Just wondering if it's correct though.

Is there an actual question hidden somewhere? Help me spot it please. — Till Helge
– Till Helge, Commented Nov 1, 2011 at 13:16
The high level design seems to be off, if you ask me. Why do you have quantity in both the Item class and the CartItem class? You should leave quantity to the CartItem class and focus on just the attributes of an individual product for the Item class, e.g., price, description, etc. — ladaghini
– ladaghini, Commented Nov 1, 2011 at 13:24
yeahh,I'm trying to understand the underlying reason behind it too based from the lecturer's design..it was already designed in the first place and all the specifications were already given to us and we have to follow it strictly. — yoshifish
– yoshifish, Commented Nov 1, 2011 at 13:26
Having read the teacher's design, the quantity attribute in Item is in fact an available quantity (in stock) for this item. — JB Nizet
– JB Nizet, Commented Nov 1, 2011 at 15:16

Jon Skeet · Accepted Answer · 2011-11-01 13:15:54Z

2

No, it's not correct. Look at your constructor:

public CartItem(Item itemName, int itemQuantity) {
    this.getItem();
    this.getQuantity();
}

Here you're calling the getters and completely ignoring the values the caller has passed in. I don't think you want to do that... think about what the constructor needs to do in order to populate the newly constructed object...

(You should also consider making these classes immutable, but that's a slightly different matter.)

answered Nov 1, 2011 at 13:15

Jon Skeet

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Comments

Jigar Joshi · Accepted Answer · 2011-11-01 13:17:52Z

0

Few things.

1 Person may shop more than one Item so have List of Item
2 Constructor isn't correct, which should be

public CartItem(Item itemName, int itemQuantity) {
        this.item = itemName;
        this.itemQuantity = itemQuantity;

    }

answered Nov 1, 2011 at 13:17

Jigar Joshi

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1 Comment

JB Nizet Over a year ago

The list should be in the Cart object, and it would be a List<CartItem>.

JB Nizet · Accepted Answer · 2011-11-01 13:20:32Z

No it's not.

The constructor for CartItem just calls this.getItem() and this.getQuantity(). This will just call the methods, which will obviously return null, since the attributes are never initialized. It should be:

public CartItem(Item itemName, int itemQuantity) {
    this.item = itemName;
    this.itemQuantity = itemQUantity;
}

Another problem is that you add getters and setters for all the fields, without even knowing if those methods are necessary. Try to favor immutability, and only provide setters if they are absolutely necessary. I won't explain all the advantages of immutability, because it would be too early given what you already know. But a good rule of thumb is : don't add a method to a class if it's not used.

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