is there any kind of reverse_iterator in List, just to reverse the List? (Java8 stream solution preferred)

Question

I am wondering if there are some kind of reverse_iterator(like c++) in List implementation like ArrayList<Integer>. i.e, I would like to iterate from the end of the List rather than from the beginning?

Is there any Java8 stream solution?

All Standard java api classes are documented in Javadoc https://docs.oracle.com/javase/8/docs/api/java/util/List.html — Erwin Bolwidt, Oct 28 '18 at 05:08
`IntStream.rangeClosed(1, list.size()).map(i -> list.size() - i).mapToObj(list::get).iterator()` — shmosel, Oct 28 '18 at 06:14
maybe your answer is right, but could you explain, too long to be understandable. :-) @shmosel — Adam Lee, Oct 28 '18 at 07:06

score 6 · Accepted Answer · answered Oct 28 '18 at 05:05

6

In java there is List Iterator https://www.journaldev.com/13457/java-listiterator

// Substitute appropriate type.
ArrayList<...> a = new ArrayList<...>();

// Add elements to list.

// Generate an iterator. Start just after the last element.
ListIterator li = a.listIterator(a.size());

// Iterate in reverse.
while(li.hasPrevious()) {
  System.out.println(li.previous());
}

answered Oct 28 '18 at 05:05

Amit Kumar Lal

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Although your answer is correct, I would like to see if there is some elegant Java8 solution:-) let's wait for some more time – Adam Lee Oct 28 '18 at 09:31

score 1 · Answer 2 · answered Oct 28 '18 at 14:58

Another way you could have reversed the list is to use Collections.reverse

ArrayList<Integer> a = new ArrayList<>(); // assign some values here
a.forEach(System.out::println); // actual order
Collections.reverse(a);
a.forEach(System.out::println); // reverse order

score 0 · Answer 3 · answered Oct 28 '18 at 05:58

Yes there is a option for reverse iteration in java.Below code works fine.

ArrayList<Integer> al = new ArrayList<>();
al.add(1);
al.add(2);
al.add(3);
al.add(4);

ListIterator<Integer> itr = al.listIterator(al.size());

System.out.println("Printing from last element ");
while (itr.hasPrevious()) {
    System.out.println(itr.previous());
}

is there any kind of reverse_iterator in List, just to reverse the List? (Java8 stream solution preferred)

3 Answers3