Need help sorting ArrayList

Question

1.00/5 (2 votes)

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Can any one tell me how to sort this out pardon the pun

C#

private void sort( ){

             String[] names = (String[]) members.toArray();
             sortStringExchange (names);
             for ( int k = 0;  k < members.size();  k++ )
            System.out.println(names[k] );
      }

      public static void sortStringExchange( String  x [ ] )
      {
            int i, j;
            String temp;

            for ( i = 0;  i < x.length - 1;  i++ )
            {
                for ( j = i + 1;  j < x.length;  j++ )
                {
                         if ( x [ i ].compareToIgnoreCase( x [ j ] ) > 0 )
                          {                                             // ascending sort
                                      temp = x [ i ];
                                      x [ i ] = x [ j ];    // swapping
                                      x [ j ] = temp;

                           }
                   }
             }
      }

Posted 24-Apr-14 6:15am

paul power

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PIEBALDconsult 24-Apr-14 12:32pm

What seems to be the problem?

paul power 24-Apr-14 12:36pm

I have an Arraylist of members and im trying to convert them to strings to sort them alphabetically

2 solutions

Solution 1

The idea is to use the custom comparator, which should be some class implementing the interface Comparable<T>, where T should be the the type of the element of your list (or, possibly, the common base type of the runtime types of the elements of the list, abstract or not). Please see:
http://docs.oracle.com/javase/6/docs/api/java/lang/Comparable.html[^].

You will find some code sample here: http://stackoverflow.com/questions/2784514/sort-arraylist-of-custom-objects-by-property[^].

Now, this makes no sense and won't cast:

Java

String[] names = (String[])members.toArray();

In your code, you should compare strings representing elements, not lists or arrays of elements. Instead, you should use java.lang.Object.toString() which you could override in your element class(es). Please see:
http://docs.oracle.com/javase/7/docs/api/java/lang/Object.html[^].

—SA

Posted 24-Apr-14 7:23am

Sergey Alexandrovich Kryukov

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BupeChombaDerrick · Accepted Answer · 2014-04-24T10:46:00

Solution 2

Try this

Java

private void sort( ){

             String[] names = (String[]) members.toArray();
             // Remove this line
             //sortStringExchange (names);
             // add this using comparator as stated by Sergey
             Arrays.sort(names, new Comparator<string>() {

                @Override
                public int compare(String s1, String s2) {

                return s1.compareTo(s2);

           }
});
            
             for ( int k = 0;  k < members.size();  k++ )
              System.out.println(names[k] );
      }

Hope this helps :)

BCD

Posted 24-Apr-14 10:46am

BupeChombaDerrick

Updated 24-Apr-14 10:48am

v2

Comments

BupeChombaDerrick 24-Apr-14 17:22pm

In String[] names = (String[]) members.toArray();

What is members? Maybe it is the cast that is the problem.

paul power 24-Apr-14 17:34pm

Maybe i'm going about it wrong i can get the arraylist of members and index with the following code but i have to be able to get them back in alphabetical order using a sort method and i'm not allowed to use the use of a Java lib.

public void listNames() {
for (int i = 0; i < members.size(); i++) {
Member member = members.get(i);
member.getName();
StdOut.println(i + ":" + member.getName());
}
}