Sort List<List<String>> by list value

Question

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

Answer 1

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

Answer 2

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?