asked on

sorting fields in arraylist

hi guys

I have a array list 'myItems' which contains objects of type Object1.

Now Object1 has fields

private String name = "";
private int age=0;
private java.sql.Date date;

set() //for all the three fields
get() //for all the three fields

now
if (condition1 is true)
{
//i want to display all 'names' in the arraylist in ascending order
}

else if (condition2 is true)
{
//i want to display all 'age' in the arraylist in ascending order
}

else if (condition3 is true)
{
//i want to display all 'dates' in the arraylist in ascending order
}

any idea how i can display the 'names' or 'age' or 'dates' in ascending order
thanks
J

Mick Barry

use three different Comparators

http://java.sun.com/docs/books/tutorial/collections/algorithms/

jaggernat

ASKER

any code would greatl help

thanks
J

Mick Barry

public class ByName implements Comparator
{
public int compare(Object _a, Object _b)
{
Object1 a = (Object1) _a;
Object1 b = (Object1) _b;
return a.getName().compareTo(b.getName());
}

jaggernat

ASKER

ok, the above method will return an int value, but i want to return the list of 'names' in ascending order.
Also, is it possible to return the list of names in descending order?

thanks verymuch
J

Mick Barry

thats just the comparator, you would use that to sort your list

Collections.sort(myItems, new ByName());

jaggernat

ASKER

ok, got it, thanks.

will Collections.sort(myItems, new ByName());
display in ascending order? Actually my requirment is i want it to be displayed in Desceding order as well.
any ideas?

thanks

Mick Barry

to reverse order use:

Collections.sort(myItems, Collections.reverseComparator(new ByName()));

jaggernat

ASKER

thanks very much.

i will try this code first thing tomorrow morning.

any ideas with my next question grealty appreciated.
thanks,
https://www.experts-exchange.com/questions/22627444/display-elements-from-List-in-descending-order.html

jaggernat

ASKER

hi objects

why does it say method reverseComparator is undefined for the type Collections

thanks

ASKER CERTIFIED SOLUTION

Mick Barry

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See answer

jaggernat

ASKER

do you think it should be

Collections.sort(myItems, new OrderEntryComparator());
Collections.reverseOrder();

thanks

Mick Barry

Collections.sort(myItems, Collections.reverseOrder(new OrderEntryComparator()));

jaggernat

ASKER

ok
says the method reverseOrder() is not applicable for arguments OrderEntryComparator

Mick Barry

sounds like it does not implement Comparator

jaggernat

ASKER

it does . reverseOrder() method doesnt take any arguments.

Mick Barry

see the link i posted above :)

jaggernat

ASKER

anyway
this seems to work

Collections.sort(myItems, new OrderNumberComparator());
Collections.reverseOrder();

but the date comparision doesnt work. should the date also be compared like :

public class OrderDateComparator implements Comparator
{

      public int compare(Object obj1, Object obj2) {

            OrderEntry oe1 = (OrderEntry) obj1;
            OrderEntry oe2 = (OrderEntry) obj2;

                  return - (oe1.getOrderDate().compareTo(oe2.getOrderDate()));
            }

}

thanks

jaggernat

ASKER

the date is of the type java.sql.Date