Change LinkedHashMap items in reverse order

Question

I would like to change the elements in my LinkedHashMap in the reverse order. Something like this:

public static void main(String[] args){
    Map<String, Integer> map = new LinkedHashMap<>();
    map.put("Hello", 2);
    map.put("World", 1);
    reverse(map);
    System.out.println(map);// {Wordl=1, Hello=2}
}

public static void reverse(Map<String, Integer> map){
   // Reverse my map...
}

But I did not find anything that could help me to do this. Can someone suggest how this can be solved? Thank.

@Jabongg I don't think this is what OP needs, he needs something that produces `{Hello=2, Wordl=1}` I think... — A4L, Jan 09 '19 at 12:25
@Jabongg - That Q&A is about creating an inverse map. This is not a dup of that one. — Stephen C, Jan 09 '19 at 12:27
Yaah! you are right. it's about reversing the whole map. Thanks Stephen C @A4L — Jabongg, Jan 09 '19 at 12:29
@Jabongg, In this issue are swapped keys and values. I have another question. — Stan, Jan 09 '19 at 12:30

score 1 · Accepted Answer · answered Jan 09 '19 at 12:31

1

You can use this code to iterate in reverse order:

   ListIterator<Map.Entry<String, Integer>> iterator = new ArrayList<Map.Entry<String, Integer>>(map.entrySet()).listIterator(map.size());
            while (iterator.hasPrevious()) {
                Map.Entry<String, Integer> entry = iterator.previous();
                System.out.println(entry.getValue());
            }

answered Jan 09 '19 at 12:31

Ehsan Mashhadi

2,568
1
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@StasUmanets Your welcome, Don't forget vote up! – Ehsan Mashhadi Jan 09 '19 at 15:05
1

Since Java 7, you can write `new ArrayList<>(map.entrySet())` instead of `new ArrayList>(map.entrySet())` – Holger Jan 11 '19 at 10:31

score 0 · Answer 2 · answered Jan 09 '19 at 12:26

0

Have you looked here:

How to traverse Linked Hash Map in reverse?

Check out the second answer which offers options on how to traverse. Also see the link to the Guava library.

answered Jan 09 '19 at 12:26

Happy

59
6

Ok, i will check Guava library. – Stan Jan 09 '19 at 13:08

score 0 · Answer 3 · answered Jan 09 '19 at 12:28

// You can do take use of Arraylist. Here's an implementation.

    public static void main(String[] args) {

    Map<String, String> map = new LinkedHashMap<String, String>();
    map.put("Hello", "2");
    map.put("World", "1");
    // create an arraylist initialized with keys of map
    ArrayList keyList = new ArrayList(map.keySet());
    for (int i = keyList.size() - 1; i >= 0; i--) {
        // get key
        String key = (String) keyList.get(i);
        System.out.println("Key :: " + key);
        // get value corresponding to key
        String value = map.get(key);
        System.out.println("Value :: " + value);
        System.out.println("--------------------------------");
    }
}

Change LinkedHashMap items in reverse order

3 Answers3