how to sort an arraylist that contains string arrays?

Question

List<String[]> allWordList = new ArrayList<>();

I would like to sort the "allWordList" list based on the first element in string array alphabetically.

I have a list that contains string array which are of size 2. So basically i want to sort this list by comparing the first element of the string array.

Collection.sort();

does not work as it is used to sort......

List<String>

and not

List<String[]>

to be clear i do not want to sort the individual string[] elements. I would like to sort the entire list based on the very first element of the string array.

Answer 1

A simple custom comparator should do the trick.

The only tricky thing is making sure that you are not indexing into an empty array:

Collections.sort(allWordList, new Comparator<String[]>() {
    public int compare(String[] o1, String[] o2) {
        if (o1.length == 0) {
            return o2.length == 0 ? 0 : -1;
        }
        if (o2.length == 0) {
            return 1;
        }
        return o2[0].compareTo(o1[0]);
    }
});

Answer 2

您可以提供自己的比较器，例如作为lambda表达式：

allWordList.sort((o1, o2) -> o1[0].compareTo(o2[0]));

Answer 3

I'd go with a variation of @dasblinkenlight 's answer where I'd don't think comparing array length's is correct behavior.

private void sort() {
    List<String[]> allWordList = new ArrayList<String[]>();
    // fill the list...
    Collections.sort(allWordList, new FirstElementComparator());
    // and so on...
}

private static class FirstElementComparator implements Comparator<String[]>
{
    @Override
    public int compare(String[] sa1, String[] sa2) {
        String str1 = sa1[0];
        String str2 = sa2[0];

        int result = 0;
        if (str1 == null) {
            result = (str2 == null) ? 0 : -1;
        }
        else {
            result = str1.compareTo(str2);
        }
        return result;
    }
}

Answer 4

You don't need to write your own Comparator :

allWordList
    .stream()
    .sorted(Comparator.comparing(a -> a[0], String.CASE_INSENSITIVE_ORDER))
    .collect(Collectors.toList());

You can omit the String.CASE_INSENSITIVE_ORDER if the ordering should be case-sensitive.

Or if you need locale-dependent ordering, take a look at Collator .

Answer 5

Check This :

Collections.sort(list, new Comparator<String>() {
        @Override
        public int compare(String s1, String s2) {
            return s1.compareToIgnoreCase(s2);
        }
    });

Source from here

Option 2 :

Collections.sort(teamsName.subList(1, teamsName.size()));

Source from here