Java Language Streams Using IntStream to iterate over indexes


Streams of elements usually do not allow access to the index value of the current item. To iterate over an array or ArrayList while having access to indexes, use IntStream.range(start, endExclusive).

String[] names = { "Jon", "Darin", "Bauke", "Hans", "Marc" };

IntStream.range(0, names.length)
    .mapToObj(i -> String.format("#%d %s", i + 1, names[i]))

The range(start, endExclusive) method returns another ÌntStream and the mapToObj(mapper) returns a stream of String.


#1 Jon
#2 Darin
#3 Bauke
#4 Hans
#5 Marc

This is very similar to using a normal for loop with a counter, but with the benefit of pipelining and parallelization:

for (int i = 0; i < names.length; i++) {
    String newName = String.format("#%d %s", i + 1, names[i]);