Collections.sort(String), doesn't work for me?

Question

ok. Rookie question.

I have a scanned string that i would like to sort using Collections.sort(string).

The string comes from a scanned file that has a bunch of "asdfasdfasdf" in it.

I have scanned the file (.txt) and the scannermethod returns a String called scannedBok;

The string is then added to an ArrayList called skapaArrayBok();

here is the code:

public ArrayList<String> skapaArrayBok() {

ArrayList<String> strengar = new ArrayList<String>();

strengar.add(scanner());
Collections.sort(strengar);

return (strengar);
}

in my humble rookie brain the output would be "aaadddfffsss" but no.

This is a schoolasigment and the whole purpose of the project is to find the 10 most frequent words in a book. But i can't get it to sort. But i just would like to know why it won't sort the scanned string?

The question asker has failed to read the Java API documentation carefully. — Bobulous, Aug 06 '14 at 18:36
I would use `new String(Arrays.sort(scanner().toCharArray()));` — njzk2, Aug 06 '14 at 18:36
A List of one element is sorted. Do you want to sort characters in the String? — Elliott Frisch, Aug 06 '14 at 18:36
@Zhuinden What evidence do you have that a collection of String would be sorted by reference? — Bobulous, Aug 06 '14 at 18:38
@Zhuinden String implements `Comparator` and has a `compareTo` method; why would the collection be sorted by reference rather than the content of the String? — Anthony Grist, Aug 06 '14 at 18:39
user3433370 - just input more strings, and you should be golden. Look at my example before for more details, if you wish. — FoggyDay, Aug 06 '14 at 18:45
@AnthonyGrist valid point, I deleted my statement because it was incorrect — EpicPandaForce, Aug 06 '14 at 18:46

score 3 · Accepted Answer · answered Aug 06 '14 at 18:34

3

You are sorting the list, not the String. The list has only one element, so sorting it doesn't change anything.

In order to sort the content of the String, convert it to an array of characters, and sort the array.

answered Aug 06 '14 at 18:34

Eran

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FoggyDay · Answer 2 · 2014-08-06T18:41:51.983

Collections.sort() sorts the items in a list.

You have exactly one item in your list: the string "aaadddfffsss". There's nothing to sort.

SUGGESTIONS:

1) Read more strings into your collection

  public ArrayList<String> skapaArrayBok() {

    ArrayList<String> strengar = new ArrayList<String>();

    // Input three strings
    strengar.add(scanner());
    strengar.add(scanner());
    strengar.add(scanner());

    // Now sort
    Collections.sort(strengar);

... or ...

2) Split the string into characters, and sort the characters.

  public ArrayList<String> skapaArrayBok() {

    // Get string    
    String s = scanner());
    char[] charArray = s.toCharArray();
    Arrays.sort(charArray );

    // Return sorted string
    return (new String(charArray);

score 0 · Answer 3 · answered Aug 06 '14 at 18:36

It is correct to sort "strengar", the ArrayList. However, it would not change the ordering of the ArrayList if you've only added one String to it. A list with one element is already sorted. If you want to sort the ArrayList, you should call add() on the ArrayList with each String you need to add, then sort.

score 0 · Answer 4 · edited May 23 '17 at 11:57

0

You want to sort the characters within the String which is completely different and you need to re-organize the characters, a possible solution (especially knowing that Strings are immutable) is the following Sort a single String in Java

edited May 23 '17 at 11:57

Community

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answered Aug 06 '14 at 18:38

EpicPandaForce

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The type `String` implements `Comparable` so it has a natural ordering. So `Collections.sort(List)` will sort the items in the `List` by the natural order of the String content, not by reference. Delete point one from your answer and I'll remove the downvote. – Bobulous Aug 06 '14 at 18:43

Collections.sort(String), doesn't work for me?

4 Answers4