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MohanMaverick
MohanMaverick

Reputation: 91

Sort List<List<String>> by list value

I want sort the List by values in the list , it contains three values , first value is integer i convert that into string and other two values are string in nature, i want to sort the list by first string .

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

List<String> fieldValues =fieldValues = new ArrayList<String>();
String aString = Integer.toString(ScreenId);
fieldValues.add(aString);
fieldValues.add(DisplayScreenName);
fieldValues.add(TableDisplay);

detail_View.add(fieldValues);

In above code i have to sort list values by ScreenId

Upvotes: 5

Views: 10782

Answers (4)

Oliv
Oliv

Reputation: 10812

Java 8 version:

Collections.sort(fieldValues, Comparator.comparing(e -> e.get(0)));

This version will sort the integers as numbers, not as strings:

Collections.sort(fieldValues, Comparator.comparing(e -> Integer.valueOf(e.get(0))));

Upvotes: 1

Sam
Sam

Reputation: 6890

You have to use two concept:

  1. Collections.sort utility.
  2. Comparator<T> interface.

I write your solved problem following:

First you have to write your comparator:

class CustomComparator implements Comparator<List<String>>
    {
        @Override
        public int compare(List<String> o1,
            List<String> o2)
        {
            String firstString_o1 = o1.get(0);
            String firstString_o2 = o2.get(0);
            return firstString_o1.compareTo(firstString_o2); 
        }
    }

then you using Collections utility as following:

Collections.sort(detail_View, new CustomComparator());

after these step, your list:

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

will sorted by first index of any nested list.

For more information related to this concept see:

  1. http://www.javadeveloper.co.in/java-example/java-comparator-example.html
  2. http://www.roseindia.net/java/java-tips/data/collections_non_generic/comparators.shtml

Upvotes: 4

Louis Wasserman
Louis Wasserman

Reputation: 198023

Make a class with the three fields; don't move them around as a List<String>, that's just silly. Making that class comparable will let you sort them as you like.

Upvotes: 2

Thilo
Thilo

Reputation: 262474

Supposing that you do not want to sort the integer (stored as a String) alphabetically, you cannot use the default comparator, but have to convert it back to an integer first:

Collections.sort(detail_view, new Comparator<List<String>>(){
    int compareTo(List<String> a, List<String> b){
         return Integer.valueOf(a.get(0)).compareTo(Integer.valueOf(b.get(0));
    }
});

May I suggest not using a List for the three pieces of data, but your own bean class?

Upvotes: 3

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