Java Generics error while compiling

Question

Example

    private static final Comparator<A> PRODUCT_CODE_COMPARATOR = new Comparator<A>()
{
    @Override
    public int compare(final A o1, final A o2)
    {
        return o1.getCode().compareTo(o2.getCode());
    }
};
public static <T extends A> List<T> sortProductsByCode(final Collection<T> productModels)
{
    return sortProducts(productModels, PRODUCT_CODE_COMPARATOR);
}

private static <T> List<T> sortProducts(final Collection<T> t, final Comparator<T> comparator)
{
    final List<T> variants = new ArrayList<T>(t);
    Collections.sort(variants, comparator);
    return variants;
}

Getting an error at return sortProducts(productModels, PRODUCT_CODE_COMPARATOR);

Can anyone help?

user545680 · Accepted Answer · 2011-08-25 06:36:56Z

2

You need your declaration of sortProducts to be:

private static <T> List<T> sortProducts(final Collection<T> t, 
                                        final Comparator<? super T> comparator)

This allows the Comparator to compare T's or any super class of T. Or, in other words, the method will accept Comparator<T> or Comparator<A>.

answered Aug 25, 2011 at 6:36

user545680

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