Question

I’m having a weird problem with HashMap in Android. I’m putting values into the hashmap which is of the form

HashMap <String,String> sample = new HashMap<String,String>();

However let’s say I’m putting the following values in the following order:

sample.put("ifi1", "video1");
sample.put("ifi2", "video2");
sample.put("ifi3", "video3");
sample.put("ifi4", "video4");
sample.put("ifi5", "video5");
sample.put("ifi6", "video6");
sample.put("ifi7", "video7");
sample.put("ifi8", "video8");
sample.put("ifi9", "video9");

This is just a simple example that is similar to what i have. I only have a bigger list in my actual code. However when I now try to print only the values, I get an unordered list as follows:

VIDEOS: video1
VIDEOS: video3
VIDEOS: video2
VIDEOS: video5
VIDEOS: video4
VIDEOS: video7
VIDEOS: video6
VIDEOS: video9
VIDEOS: video8

where in fact I’m expecting it to produces the following list:

VIDEOS: video1
VIDEOS: video2
VIDEOS: video3
VIDEOS: video4
VIDEOS: video5
VIDEOS: video6
VIDEOS: video7
VIDEOS: video8
VIDEOS: video9

Why is this, any idea?

Answer 1

That’s right. The HashMap implementation of Map does not guarantee any order during iteration.

If you want ordering based on insertion…

…have a look at LinkedHashMap:

Map<String, String> sample = new LinkedHashMap<String, String>();

sample.put("ifi1", "video1");
sample.put("ifi2", "video2");
sample.put("ifi3", "video3");
sample.put("ifi4", "video4");
sample.put("ifi5", "video5");
sample.put("ifi6", "video6");
sample.put("ifi7", "video7");
sample.put("ifi8", "video8");
sample.put("ifi9", "video9");

for (String video : sample.values())
    System.out.println(video);

// Prints
video1
video2
video3
video4
video5
video6
video7
video8
video9

If you want ordering based on the keys…

Use a NavigableMap or SortedMap implementation such as a TreeMap.