java字符串数组排序

Question

I have to sort list of arrays by date. I did not known how to do it, so i have added all values into one value. This is almost work fine, but it do not sort years good This is my code:

ArrayList<String> ar = new ArrayList<String>();
        String s1 ="2016|07|21 15:26:20!947!-0.0091002";
        String s2 ="2015|08|21 15:26:20!977!0.0091002";
        String s3 ="2015|07|22 15:26:20!947!1.0091002";
        String s4 ="2015|07|21 16:26:20!946!0.0091001";
        String s5 ="2015|07|21 15:27:20!977!0.0091002";
        String s6 ="2015|07|21 15:26:21!947!1.0091002";
        String s7 ="2015|07|21 15:26:20!946!0.0091001";
        ar.add(s1);
        ar.add(s2);
        ar.add(s3);
        ar.add(s4);
        ar.add(s5);
        ar.add(s6);
        ar.add(s7);
        Collections.sort(ar.subList(1, ar.size()));
        Object[][] data = {
                {ar.get(0)},
                {ar.get(1)},
                {ar.get(2)},
                {ar.get(3)},
                {ar.get(4)},
                {ar.get(5)},
                {ar.get(6)},
        };

and this is output:

2016|07|21 15:26:20!947!-0.0091002
2015|07|21 15:26:20!946!0.0091001
2015|07|21 15:26:21!947!1.0091002
2015|07|21 15:27:20!977!0.0091002
2015|07|21 16:26:20!946!0.0091001
2015|07|22 15:26:20!947!1.0091002
2015|08|21 15:26:20!977!0.0091002

but this is what I need:

2015|07|21 15:26:20!946!0.0091001
2015|07|21 15:26:21!947!1.0091002
2015|07|21 15:27:20!977!0.0091002
2015|07|21 16:26:20!946!0.0091001
2015|07|22 15:26:20!947!1.0091002
2015|08|21 15:26:20!977!0.0091002
2016|07|21 15:26:20!947!-0.0091002

And i've got no ida why is this happend

Answer 1

Simply use:

Collections.sort(ar);

to sort the entire list.

Remember that Java lists are zero-based, so ar.get(0) is the first element. List.subList(i, j) returns the sublist from i (inclusively) to j (exclusively).

So, to sort the whole list via a sublist, you'd need to use i = 0 and j = ar.size() . However, the indirection of the sublist is unnecessary: just pass the list itself to Collections.sort .

Answer 2

Here is what's wrong with your code

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

You are trying to sort indices 1~N, so index 0 is not sorted.

What you should be doing is sort the entire ArrayList like this

    Collections.sort(ar);

This will sort the ArrayList<String> in ascending order.

Output

2015|07|21 15:26:20!946!0.0091001
2015|07|21 15:26:21!947!1.0091002
2015|07|21 15:27:20!977!0.0091002
2015|07|21 16:26:20!946!0.0091001
2015|07|22 15:26:20!947!1.0091002
2015|08|21 15:26:20!977!0.0091002
2016|07|21 15:26:20!947!-0.0091002

However, your code just sorts the string list in ascending order so if you have month/date/year in different order, it will not be sorted by time. You should be using Date/Time utils available in Java or other libraries like Apache.

Answer 3

You are sorting only a view of a sublist of your list, which will have no effect on the list you actually want to return. Indeed, List.sublist returns a new list.

By the way, your code could be much shorter :

List<String> list = Arrays.asList(
    "2016|07|21 15:26:20!947!-0.0091002", "2015|08|21 15:26:20!977!0.0091002", "2015|07|22 15:26:20!947!1.0091002",
    "2015|07|21 16:26:20!946!0.0091001", "2015|07|21 15:27:20!977!0.0091002", "2015|07|21 15:26:21!947!1.0091002", "2015|07|21 15:26:20!946!0.0091001");
Collections.sort(list);