如何获取IntStream.map.forEach的索引？

Question

I have this line which prints the squares of the numbers 0 to 5:

IntStream.rangeClosed(0, 4).map(i ->i*i).forEach(System.out::println);

The output is

0
1
4
9
16

Is there a way to get the output like below?

0 :0
1 :1
2 :4
3 :9
4 :16

Answer 1

Once you map i to i*i you lose the original i .

You can remove the map and do the calculation inside the forEach :

IntStream.rangeClosed(0, 4).forEach(i -> System.out.println(i + ": " + i*i));

Answer 2

Or you could do it like this(mapping to a Pair of key/value):

IntStream.rangeClosed(0, 4)
         .mapToObj(i -> new AbstractMap.SimpleEntry<>(i, i * i))
         .forEach(System.out::println);