CODEWITHSUNDEEP
javaandroidarrayssorting
Ricky Watson
Ricky Watson

Reputation: 143

How to sort " ArrayList<HashMap<String, String>> arrList " alphabatically?

Can you guide me how can I sort Array List having Hash Map alphabatically?

JSONArray   jArr2 = new JSONArray(jsonString2);

for(int i=0;i<jArr2.length();i++){

HashMap<String, String> map = new HashMap<String, String>();
map.put("titleName",jArr2.getJSONObject(i).getString("titleName"))
programList.add(map);

}

Upvotes: 0

Views: 1273

Answers (3)

Tom McIntyre
Tom McIntyre

Reputation: 3699

Looking at your example, I don't think you need a Map to be involved at all. What you have is a list of Maps, where every Map only has one key, which is "titleName". Why not just have a list of titlenames? Then your code would look like this:

JSONArray jArr2 = new JSONArray(jsonString2);

List<String> titleNames = new ArrayList<>();

for (int i = 0; i < jArr2.length(); i++) {

    titleNames.add(jArr2.getJSONObject(i).getString("titleName"))

}

You know that the list only contains titleNames, you don't need to complicate the data structure with Maps!

Then you can sort the list simply by using

Collections.sort(titleNames);

Note that this will work while the other answers that suggests Collections.sort() on the list of maps will not work. This is because titleNamees is a List of Strings, which implement Comparable (ie the sort() method knows how to order them with respect to each other), while Map does not implement comparable (as there are multiple ways to order Maps - number of entries, total number of bytes, etc).

Upvotes: 1

eluleci
eluleci

Reputation: 3529

Yes you can use Collections.sort(); with a custom comparator. Here is the doc.

Collections.sort(YOUR_ARRAY_LIST, new YourCustomComparator());

And this should be the class you must have

class YourCustomComparator implements Comparator<HashMap<String, String>> {

    @Override
    public int compare(HashMap<String, String> lhs, HashMap<String, String> rhs) {

        // check here your objects. lhs and rhs. compare them as you want
        // return 1 if lhs is greater than rhs
        // return 0 if ther are same
        // return -1 otherwise
    }
}

Upvotes: 0

Umang Mehta
Umang Mehta

Reputation: 1497

Implement a Comparator<HashMap<String, String>> which just extracts the value assocated with the value key, then use Collections.sort method to sort your arraylist.

For e.g.:

class MyComparator implements Comparator<Map<String, String>>{

    private final String key;

    public MyComparator(String key)
    {
        this.key = key;
    }

    public int compare(Map<String, String> first,
                       Map<String, String> second)
    {
        // TODO: Null checking, both for maps and values
        String firstValue = first.get(key);
        String secondValue = second.get(key);
        return firstValue.compareTo(secondValue);
    }
}

Upvotes: 2

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