CODEWITHSUNDEEP
javaandroid
bytebiscuit
bytebiscuit

Reputation: 3496

HashMap gives an unordered list of values?

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?

Upvotes: 10

Views: 22514

Answers (8)

aioobe
aioobe

Reputation: 420951

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.

Upvotes: 33

mihail
mihail

Reputation: 2173

LinkedHashMap<T, T>

keep the insert order

Upvotes: 0

neeraj t
neeraj t

Reputation: 4754

If you use Simple HashMap then this class use some hashing technique to store the value ,at the time of extracting the data from list its use same hash technique. And Hash function are not ordered. that's why result is coming unordered. In Placed of HashMap you have to use LinkedHashMap to make it ordered List.

Upvotes: 0

anujprashar
anujprashar

Reputation: 6335

In HashMap order is not there. Try using LinkedHashMap instead. LinkedHashMap keeps track of the keys based on insertion order, so that when you do a call to getKeySet(), you will get the keys back in the order you put them in.

Upvotes: 4

Miguel Prz
Miguel Prz

Reputation: 13792

look for a class that implements SortedMap interface. Or for print purposes only, you can order de Set returned from your Map with Collections.sort

Upvotes: 0

Xavi L&#243;pez
Xavi L&#243;pez

Reputation: 27880

You can also use a LinkedHashMap in order to obtain the collection of entries in the same order they were inserted in.

Upvotes: 0

Jigar Joshi
Jigar Joshi

Reputation: 240890

Use LinkedHashMap instead

Upvotes: 3

Sasha Goldshtein
Sasha Goldshtein

Reputation: 3519

You need to use SortedMap instead of HashMap. It will guarantee order.

Upvotes: 5

Related Questions