null pointer exception in array

Question

I am getting a null exception error from this segment of code and I am not sure what causing it. The array itemcatalog has being populate for i =0 to 8. I am new to java so any assistance will be greatly appreciated. The error message points to the line of the while statement. Thanks

public class ItemCatalog {

   private static ItemCatalog instance = new ItemCatalog(); 
   private Item itemCatalog[] = new Item[9];

   private ItemCatalog(){
   };

   public static synchronized ItemCatalog getInstance() {
   return instance;
   }

   public void populateCatalog()
   {  
      itemCatalog[0] = new Item("bb","Baked Beans",new BigDecimal("0.35"));
      itemCatalog[1] = new Item("cf","Cornflakes",new BigDecimal("1.00"));
      itemCatalog[2] = new Item("s0","Sugar",new BigDecimal("0.50"));
      itemCatalog[3] = new Item("tb","Tea Bags",new BigDecimal("1.15"));
      itemCatalog[4] = new Item("ic","Instant Coffee",new BigDecimal("2.50"));
      itemCatalog[5] = new Item("b0","Bread",new BigDecimal("0.50"));
      itemCatalog[6] = new Item("s0","Sausages",new BigDecimal("1.30"));
      itemCatalog[7] = new Item("e0","Eggs",new BigDecimal("0.75"));
      itemCatalog[8] = new Item("m0","Milk",new BigDecimal("0.65"));
   }

   public BigDecimal getPrice(String itemCode)
   {  

      int i = 0;
      while (!itemCode.equals(itemCatalog[i].getItemCode()))
      {
        i++;
      }
      BigDecimal itemPrice = itemCatalog[i].getItemprice();
   return itemPrice;
   }
}

I solved the issue. I was populating the catalog in the main class which was giving the null exception error. I instantiate it in the jframe instead and it works. The follow code solved the issue, but is this the best place to populate the catalog?

private void saleButtonActionPerformed(java.awt.event.ActionEvent evt) {                                           

        String itemCode = this.itemCodeinput.getText();
        int itemQuantity =Integer.parseInt(this.itemQuantityinput.getText());

        ItemCatalog catalog = ItemCatalog.getInstance();

        catalog.populateCatalog(); 
        BigDecimal price = catalog.getPrice(itemCode);
        itemCostoutput.setText(price.toString());
}

Regarding the stack trace : tell us where is the line in error. — Denys Séguret
– Denys Séguret, Commented Oct 17, 2012 at 20:10

sampson-chen · Accepted Answer · 2012-10-17 20:13:24Z

2

If your itemCode doesn't match any entries in your itemCatalog, then eventually

  while (!itemCode.equals(itemCatalog[i].getItemCode()))
  {
      i++;
  }

will increment i to 11, in which case itemCatalog[11] is either empty or out of bounds.

If addition, you should use a for loop to iterate through the itemCatalog:

for (int i = 0; i < itemCatalog.length; i++) {
    if (itemCode.equals(itemCatalog[i].getItemCode()) {
        return (BigDecimal) itemCatalog[i].getItemprice();
    }
}

return null // you can change this from null to a flag 
            // value for not finding the item.

answered Oct 17, 2012 at 20:13

sampson-chen

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3 Comments

Bob Cross Over a year ago

Also note the original comment: he's populating from 1 - 10. There's no assurance that itemCatalog[0] isn't null.

sampson-chen Over a year ago

That's a good point, I just assumed he meant the first 10 items without considering that he might have skipped 0 in his implementation

Adesh Over a year ago

Thanks alot for everyone's comments thus far. I changed out my while loop with the for loop and still get a null point exception at the if statement line.

Denys Séguret · Accepted Answer · 2012-10-17 20:15:02Z

0

From the comments, it's clear the design isn't sound.

Here's a possible solution :

public BigDecimal getPrice(String itemCode) {  
      for (int i=0; i<itemCatalog.length; i++) { // not going outside the array
          if (itemCatalog[i].getItemCode().equals(itemCode)) { // inversing the test to avoid npe if itemCode is null
             return itemCatalog[i].getItemprice();
          }
      }
      return null; // default value
}

This supposes your array is correctly filled with itemCatalogs having an itemCode.

answered Oct 17, 2012 at 20:15

community wiki

Denys Séguret

Comments

Tinman · Accepted Answer · 2012-10-17 20:20:55Z

0

How do you end your loop? Seems that the loop will keep going until i is 10. Then your will have exceeded the limit.

Unless this is a uni assignment where you have to use arrays, I'd also suggest using a map, rather than an array. This way your lookup will be the same time, whether your collection has 100,000 entries or 10.

You will also reduce risk of NPE or ArrayOutOfBounds exception

See http://docs.oracle.com/javase/1.4.2/docs/api/java/util/HashMap.html

When adding the object use the item code as the key. Then lookup by the key.

The cost of using a map is increased memory usage.

edited Oct 17, 2012 at 20:20

answered Oct 17, 2012 at 20:14

Tinman

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