How do I fix "The expression of type List needs un

Question

In the Java snippet:

SyndFeedInput fr = new SyndFeedInput();
SyndFeed sf = fr.build(new XmlReader(myInputStream));
List<SyndEntry> entries = sf.getEntries();

the last line generates the warning

"The expression of type List needs unchecked conversion to conform to List<SyndEntry>"

What's an appropriate way to fix this?

Answer 1

It looks like SyndFeed is not using generics.

You could either have an unsafe cast and a warning suppression:

@SuppressWarnings("unchecked")
List<SyndEntry> entries = (List<SyndEntry>) sf.getEntries();

or call Collections.checkedList - although you'll still need to suppress the warning:

@SuppressWarnings("unchecked")
List<SyndEntry> entries = Collections.checkedList(sf.getEntries(), SyndEntry.class);

Answer 2

Did you write the SyndFeed?

Does sf.getEntries return List or List<SyndEntry>? My guess is it returns List and changing it to return List<SyndEntry> will fix the problem.

If SyndFeed is part of a library, I don't think you can remove the warning without adding the @SuppressWarning("unchecked") annotation to your method.

Answer 3

If you look at the javadoc for the class SyndFeed (I guess you are referring to the class com.sun.syndication.feed.synd.SyndFeed), the method getEntries() doesn't return java.util.List<SyndEntry>, but returns just java.util.List.

So you need an explicit cast for this.

Answer 4

Even easier

return new ArrayList<?>(getResultOfHibernateCallback(...))

Answer 5

If you don't want to put @SuppressWarning("unchecked") on each sf.getEntries() call, you can always make a wrapper that will return List.

See this other question

Answer 6

If you are using Guava and all you want to do is iterate through your values:

for(SyndEntry entry: Iterables.filter(sf.getEntries(), SyndEntry.class){
  ...
}

If you need an actual List you can use

List<SyndEntry> list = Lists.newArrayList(
    Iterables.filter(sf.getEntries(), SyndEntry.class));

or

List<SyndEntry> list = ImmutableList.copyOf(
    Iterables.filter(sf.getEntries(), SyndEntry.class));