Why am I getting this Unsupported Operation Exception?

[ozzyman]

This error is new to me and I can't quite grasp why it occurs. Here are my error messages:

Exception in thread "AWT-EventQueue-0" java.lang.UnsupportedOperationException
at java.util.AbstractList.add(AbstractList.java:131)
at java.util.AbstractList.add(AbstractList.java:91)
at ozzypos.Products.addNewPrice(Products.java:49)
at ozzypos.ozzyPosGUI.initProducts(ozzyPosGUI.java:60 60)
...

And this is the code:

//Products.java
48        public void addNewPrice(double newPrice, boolean newPpkg, String newPDesc) {
49            productPrices.add(new ProductPrices(newPrice, newPpkg, newPDesc));
50        }

This method was invoked by this code:

//ozzyPosGUI.java
6059        Products.Product p1 = myProducts.addNewProduct("Product Name", 55.55, false, "Bronze", Products.ProductGroups.GROUP_2);
6060        p1.addNewPrice(99.99, false, "Silver");

I had a feeling that it was because Product p1 is not a reference of the product I mean to edit, please look at the addNewProduct method to see what I mean:

//Products.java
87    public Product addNewProduct(String pName, double pPrice, boolean pPpkg, String pDesc, ProductGroups pGroup) {
88        Product p = new Product();
89        p.setProductDescription(pName);
90        p.setProductPrices(new ProductPrices(pPrice, pPpkg, pDesc));
91        p.setProductGroups(pGroup);
92        productSet.add(p);
93        return p;
94    }

Any clue anyone? :confused:

[JosAH]

This error is new to me and I can't quite grasp why it occurs. Here are my error messages:

Exception in thread "AWT-EventQueue-0" java.lang.UnsupportedOperationException
at java.util.AbstractList.add(AbstractList.java:131)
at java.util.AbstractList.add(AbstractList.java:91)
at ozzypos.Products.addNewPrice(Products.java:49)
at ozzypos.ozzyPosGUI.initProducts(ozzyPosGUI.java:60 60)
...

And this is the code:

Wrong parts of the code; look at line 49 of your method addNewPrice( ... ). It directly calls method add( ... ) in the AbstractList class; an abstract list doesn't know how to add an element to itself and it is supposed to be overridden. Are you by any chance extending the AbstractList class yourself?

kind regards,

Jos

[ozzyman]

Thanks again JosAh.

Oh I see... so I think its a problem translating the List, because I am not extending the List class, because my field and constructor makes it an ArrayList, which has an add(Object) method.

        private List<ProductPrices> productPrices;
        Product() {
            productPrices = new ArrayList<ProductPrices>();
        }

So what I now think is going on is that when I do this:

        public void setProductPrices(ProductPrices... prices) {
            productPrices.clear();
            productPrices = Arrays.asList(prices);
        }

...Then it stops being an ArrayList?

[ozzyman]

Also the first price is added fine with the 'addNewProduct(...)' method but its when I try to add the second price with 'addNewPrice' I get this error, and I've even printed all the products with the prices with pricesList.get(0).getPrice() and it was fine.

[ozzyman]

Yeap, that was the problem.

This longer-winded 'setProductPrices' method straightened the problem out:

        public void setProductPrices(ProductPrices... prices) {
            List<ProductPrices> newProductPrices = new ArrayList<ProductPrices>();
            newProductPrices.addAll(Arrays.asList(prices));
            productPrices.clear();
            productPrices = newProductPrices;
        }

Problem solved :).

[JosAH]

Thanks again JosAh.

Oh I see... so I think its a problem translating the List, because I am not extending the List class, because my field and constructor makes it an ArrayList, which has an add(Object) method.

        private List<ProductPrices> productPrices;
        Product() {
            productPrices = new ArrayList<ProductPrices>();
        }

So what I now think is going on is that when I do this:

        public void setProductPrices(ProductPrices... prices) {
            productPrices.clear();
            productPrices = Arrays.asList(prices);
        }

...Then it stops being an ArrayList?

Yep, it is an ArrayList but another ArrayList type; i.e. the list is a list that can not change its length and all writes end up in the original array. (see the API documentation for the Arrays class and see the src.zip file for the source of the Arrays class and the nested ArrayList class). The remedy is simple:

productPrices= new ArrayList(Arrays.asList(prices));

This code snippet creates the fixed sized list (see also above) and makes a copy of it again in a new ordinary ArrayList.

kind regards,

Jos

[ozzyman]

Ah, I just thought all ArrayLists have unfixed sizes but I've never really looked deep into Lists so thanks for that. And I changed my code again :).

Cheers.