On Friday, November 14, 2014 1:14:08 PM UTC+1, Andreas Kohn wrote:
>
> Hi,
>
> While trying to find the cause for a very odd NPE I noticed that
> Configuration#setCategories() is implemented like this
>
> public Builder setCategories(Class<?>... categories) {
> toReturn.categories =
> Collections.unmodifiableList(new
> ArrayList<Class<?>>(Arrays.asList(categories)));
> return this;
> }
>
> Could someone explain why there is an explicit creation of the ArrayList
> done there? Both the result of Arrays.asList() and a java.util.ArrayList
> implement
> RandomAccess, so for Collections#unmodifiableList() nothing really should
> change there.
>
This is legal Java:
Class<?>[] classes = new Classes<?>[] { foo, bar };
builder.setCategories(classes);
classes[1] = baz;
This explicit copy prevents the builder (actually and more importantly its
toReturn) from being modified from the outside: toReturn.categories is
guaranteed to contain foo and bar, and not baz.
This is a standard pattern. Not doing the copy would actually be flagged as
a possible source of error by things like Checkstyle and/or Findbugs (can't
remember which ones flags this).
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