Assume that you want to build a copy of an ImmutableSet
/List
/Map
object but filter out some of the original entries. One way to implement that is the following:
ImmutableList.copyOf(Iterables.filter(myObject, myObject.EQUALS));
where myObject.EQUALS
is a predicate for the Iterables.filter()
operation. I think this is a pretty elegant and easy-to-read implementation. However, one builds two list objects (first through the Iterables.filter(...)
call, second through ImmutableList.copyOf(...)
) which is very inefficient.
Does anybody know of a more efficient way to do it?
I guess the best thing would be to add filter predicates to the ImmutableSet
/List
/Map
builders so that the object must be constructed only once. But unfortunately there is no such parameter.
The result of Iterables.filter()
is just a view over the data in myObject
: the new list is only built by ImmutableList.copyOf()
using the filtering iterator provided by the Iterable
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