Array to List, sorting (Java)

Asido · 08-14-2010, 08:01 PM

Hello,
Can anyone tell me what is wrong with this:

Code:

CardBase[] tmp = new CardBase[13];
System.arraycopy(deck, range*13, tmp, 0, 13);
Collections.sort(Arrays.asList(tmp));

In this place the compiler gives me an error:

Code:

cannot find symbol
symbol  : method sort(java.util.List<CardBase>)
location: class java.util.Collections
                Collections.sort(Arrays.asList(tmp));

paulsm4 · 08-14-2010, 10:28 PM

Hi -

There are two problems here:

PROBLEM 1:
Before you can "sort" something, it has to be "Sortable".

More specifically, the items in the "container" you want to sort need to implement class "Comparable".

Here's an example: we create a "list" of type "String"; "String" implements "Comparable" (by default) ... and everything works:

Code:

import java.util.*;

public class Sort {
    public static void main(String[] args) {
        List<String> list = Arrays.asList(args);
        Collections.sort(list);
        System.out.println(list);
    }
}

Quote:

javac Sort.java
java Sort I Walk the Line

[i, line, the, walk]

PROBLEM 2:
"Containers.sort()" can sort a list ...
... but not an array.

If you've got an array, you should use "Arrays.sort()" instead.

I noticed you tried to convert via "Arrays.asList()" ... but that incurs extra overhead. LOTS of extra overhead. And it didn't work

Soooooo ...

If you implemented "Comparable" in your class "CardBase" ...
... and if you used "Arrays.sort()" instead of "Containers.sort ()"
... then it *should* work (if everything else is OK)

Please read any of these links - they might help explain better than me:
http://download-llnw.oracle.com/java...hms/index.html

http://www.exampledepot.com/egs/java...SortArray.html

http://www.java-examples.com/sort-el...aylist-example

'Hope that helps .. PSM

Asido · 08-15-2010, 11:49 AM

That was very informative, thank you.
Replacing the error line with Arrays.sort(tmp) solved the problem.

By the way, in one of your link I saw pretty much the same way of sorting as I did:

Code:

String[] strArray = new String[] {"z", "a", "C"}; 
Arrays.sort(strArray, String.CASE_INSENSITIVE_ORDER);
Collections.reverse(Arrays.asList(strArray));

Speaking about Comparable implementation, CardBase is actually an interface which looks like this:

Code:

public interface CardBase {
	public int compareTo(Object o);
	public Suit setSuit();
	public Suit getSuit();
	public String getShortSuit();
}

The deck array which is being copied with System.arraycopy method to a tmp array is:

Code:

CardBase[ ] deck = new Card[52];

Card class is the class which implements CardBase and Comparable interfaces. So from my point of view everything should be ok, but still isn't.