function to check string list in order give negative result

Question

I have the below function to check if it is in order

 public boolean order(List<String> value) {
            List<String> tmp = value;
            Collections.sort(tmp);
            return tmp.equals(value);
        }

Test:

assertTrue(route.order(Arrays.asList("a", "s", "d")));
assertFalse(route.order(Arrays.asList("a", "k", "c")));

but fail at 2nd test, why is it not false?

"A", "C", "D" is already ordered, if you order it again, it will still be "A", "C", "D", so why would you expect it to be false? — Matt, Jan 11 '19 at 14:16
@fantaghirocco no, not a duplicate of that one - in this case here, even the references are equal — Hulk, Jan 11 '19 at 14:28

score 4 · Answer 1 · answered Jan 11 '19 at 14:15

Here in below line:

List<String> tmp = value;

You are just copying reference of value list argument in tmp list and hence you are sorting on tmp and indirectly value list which is one and the same.

To solve the problem change the assignment of tmp variable to:

List<String> tmp = new ArrayList<>(value);

score 2 · Answer 2 · answered Jan 11 '19 at 14:17

2

public boolean order(List<String> value) {
   List<String> tmp = new ArrayList<>(value);
   Collections.sort(tmp);
   return tmp.equals(value);
 }

answered Jan 11 '19 at 14:17

Sagar P. Ghagare

542
2
12
25

1

Could you explain what you changed and why it solves the problem? – JJJ Jan 11 '19 at 14:58
@JJJ i have given complete program with working conditon by solving his issue. – Sagar P. Ghagare Jan 11 '19 at 15:00
1

Yes, I can see that you have code in the answer. Answers are expected to also explain what the problem was and why the code solves the problem. – JJJ Jan 11 '19 at 15:00
@JJJ I understand that sir, but explanation is already given in another answer, so i given whole program logic with working condition. – Sagar P. Ghagare Jan 11 '19 at 15:02
@JJJ if you need explanation to this i can add that also. – Sagar P. Ghagare Jan 11 '19 at 15:03
Thanks, that would be great. – JJJ Jan 11 '19 at 15:05

score -2 · Answer 3 · answered Jan 11 '19 at 14:18

-2

Your asserts are negative to each other. Both arrays are sorted. Maybe you wanted ("A", "C", "B").

Also, as the fellows said before, your sort is on the original list, you have to copy it first and then to sort.

answered Jan 11 '19 at 14:18

TGH

31
7

If you wanted ("A", "C", "B"), then you should not sort the Lists, or maybe use a Comparator other than the NaturalOrder to sort them – DSantiagoBC Jan 11 '19 at 14:23
@TGH, you are right. But the real problem is not here, what you point was just a writing mistake in OP question. – vincrichaud Jan 11 '19 at 14:25

function to check string list in order give negative result

3 Answers3