I want to have a reversed list view on a list (in a similar way than List#sublist
provides a sublist view on a list). Is there some function which provides this functionality?
I don't want to make any sort of copy of the list nor modify the list.
It would be enough if I could get at least a reverse iterator on a list in this case though.
Also, I know how to implement this myself. I'm just asking if Java already provides something like this.
Demo implementation:
static <T> Iterable<T> iterableReverseList(final List<T> l) {
return new Iterable<T>() {
public Iterator<T> iterator() {
return new Iterator<T>() {
ListIterator<T> listIter = l.listIterator(l.size());
public boolean hasNext() { return listIter.hasPrevious(); }
public T next() { return listIter.previous(); }
public void remove() { listIter.remove(); }
};
}
};
}
I just have found out that some List
implementations have descendingIterator()
which is what I need. Though there is no general such implementation for List
. Which is kind of strange because the implementation I have seen in LinkedList
is general enough to work with any List
.
Use the .clone() method on your List. It will return a shallow copy, meaning that it will contain pointers to the same objects, so you won't have to copy the list. Then just use Collections.
Ergo,
Collections.reverse(list.clone());
If you are using a List
and don't have access to clone()
you can use subList()
:
List<?> shallowCopy = list.subList(0, list.size());
Collections.reverse(shallowCopy);