How to map elements of the list to their indices using Java 8 streams?

Question

Having a list of strings, I need to construct a list of objects which are effectively pairs (string, its position in the list). Currently I have such code using

Answer 1

You could do something like this:

public Robots(List<String> names) {
    this.list = IntStream.range(0, names.size())
                         .mapToObj(i -> new Robot(i, names.get(i)))
                         .collect(collectingAndThen(toList(), Collections::unmodifiableList));
}

However it may not be as efficient depending on the underlying implementation of the list. You could grab an iterator from the IntStream; then calling next() in the mapToObj.

As an alternative, the proton-pack library defines the zipWithIndex functionality for streams:

 this.list = StreamUtils.zipWithIndex(names.stream())
                        .map(i -> new Robot(i.getIndex(), i.getValue()))
                        .collect(collectingAndThen(toList(), Collections::unmodifiableList));

Answer 2

The easiest way is to stream indices:

List<Robot> robots = IntStream.range(0, names.size())
                              .mapToObj(i -> new Robot(i, names.get(i))
                              .collect(toList());