Keep the order of the map as in the arrayList before

Question

I am trying to merge line toghether to create data for my programm. Curently the merging part of the Strings in the ArrayList's buffer works well but when I output the content of the Map I am getting another of the String as they were in the ArrayList's buffer.

Is there any way to keep the order of Strings as they were in the ArrayList buffer?

Output:

Nathan Marcus Adler 
[04:43, 05:43, 12:11, 12:41, 19:11, 19:41]
Dukes of Bedford 
[04:56, 05:56, 12:24, 12:54, 19:24, 19:54]
Prince Albert 
[04:48, 05:48, 12:16, 12:46, 19:16, 19:46]
Joseph Addison 
[04:41, 05:41, 12:08, 12:38, 19:08, 19:38]
William Baker 
[04:52, 05:52, 12:20, 12:50, 19:20, 19:50]

The ouput should looks as this:

Joseph Addison 
[04:41, 05:41, 12:08, 12:38, 19:08, 19:38]
Nathan Marcus Adler 
[04:43, 05:43, 12:11, 12:41, 19:11, 19:41]
Prince Albert 
[04:48, 05:48, 12:16, 12:46, 19:16, 19:46]
William Baker 
[04:52, 05:52, 12:20, 12:50, 19:20, 19:50]
Dukes of Bedford 
[04:56, 05:56, 12:24, 12:54, 19:24, 19:54]

Code:

public static void main(String[] args) {

    ArrayList<String> buffer = new ArrayList<String>();

    buffer.add("Joseph Addison 04:41 05:41");
    buffer.add("Nathan Marcus Adler 04:43 05:43");
    buffer.add("Prince Albert 04:48 05:48");
    buffer.add("William Baker 04:52 05:52");
    buffer.add("Dukes of Bedford 04:56 05:56");

    buffer.add("Joseph Addison 12:08 12:38 ");
    buffer.add("Nathan Marcus Adler 12:11 12:41");
    buffer.add("Prince Albert 12:16 12:46");
    buffer.add("William Baker 12:20 12:50");
    buffer.add("Dukes of Bedford 12:24 12:54");

    buffer.add("Joseph Addison 19:08 19:38");
    buffer.add("Nathan Marcus Adler 19:11 19:41");
    buffer.add("Prince Albert 19:16 19:46");
    buffer.add("William Baker 19:20 19:50");
    buffer.add("Dukes of Bedford 19:24 19:54");

    Map<String, List<String>> map = new HashMap<>();
    ArrayList<PlaceTime> list = new ArrayList<PlaceTime>();

    for (String element : buffer) {
        PlaceTime part = new PlaceTime(element);
        list.add(part);

    }

    for (PlaceTime t : list) {
        if (map.containsKey(t.getPlace())) {
            // If the map already contains an entry for the place, add the
            // times to the array
            map.get(t.getPlace()).addAll(t.getTimes());
        } else {
            // Map does not contain entry for place, create a new entry
            map.put(t.getPlace(), t.getTimes());
        }
    }

    // Print out contents of map
    for (Entry<String, List<String>> entry : map.entrySet()) {
        System.out.println(entry.getKey());
        System.out.println(entry.getValue());
    }

    System.out.println("Test");

}

PlaceTime class:

public class PlaceTime {
    StringBuilder place = new StringBuilder();
    List<String> times = new ArrayList<>();;

    public PlaceTime(String placeTime) {

        DateFormat dateFormat = new SimpleDateFormat("HH:mm");
        for (String i:placeTime.split(" ")) {
            try {
                dateFormat.parse(i);
                //No exception, add as time
                times.add(i);
            } catch (Exception e) {
                //Exception, add as place name
                place.append(i).append(" ");
            }
        }
    }

    public String getPlace() {
        return place.toString();
    }

    public List<String> getTimes() {
        return this.times;
    }
}

There is no difference between your current output and desired output. Rephrase the question — Laurentiu L., Jun 10 '15 at 13:22
Use a `LinkedHashMap`instead, it maintains the insertion order. — Uma Kanth, Jun 10 '15 at 13:24

Jordi Castilla · Accepted Answer · 2015-06-10T13:33:16.680

3

use TreeMap to sort natural or customized or LinkedHashMap to mantain insertion order:

LinkedHashMap for insertion order

Hash table and linked list implementation of the Map interface, with predictable iteration order. This linked list defines the iteration ordering, which is normally the order in which keys were inserted into the map (insertion-order).

Treemap for natural or custom sorting

A Red-Black tree based NavigableMap implementation. The map is sorted according to the natural ordering of its keys, or by a Comparator provided at map creation time, depending on which constructor is used.

Instead of HashMap

This class makes no guarantees as to the order of the map; in particular, it does not guarantee that the order will remain constant over time.

edited Jun 10 '15 at 13:33

answered Jun 10 '15 at 13:29

Jordi Castilla

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`TreeMap` will sort the insertions, `LinkedHashMap` is the key. – Uma Kanth Jun 10 '15 at 13:30
It does not work with TreeMap but it works with `LinkedHashMap` – Mr Asker Jun 10 '15 at 13:33
@MrAsker check my edit.... – Jordi Castilla Jun 10 '15 at 13:33

score 1 · Answer 2 · edited Jun 10 '15 at 14:10

1

HashMap doesn't fallow the iteration order by defenition. It will even change completely when new elements are added so the order is not preserved, use LinkedHashMap instead.

It will iterate in the order in which the entries were put into the map, as desired.

Check out the documentation

edited Jun 10 '15 at 14:10

Jordi Castilla

26,609
8
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answered Jun 10 '15 at 13:27

Ahmad Sanie

3,678
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56

Keep the order of the map as in the arrayList before

2 Answers2