Collections.sort(arraylist)

[Bruce Lee]

If I use Collections.sort(arraylist), the elements in the arraylist will be
sorted by natural order. What happens when the arraylist is actually an
arraylist of arraylists - how can you sort against an object?

 

[Thomas Weidenfeller]

If I use Collections.sort(arraylist), the elements in the arraylist will be
sorted by natural order. What happens when the arraylist is actually an
arraylist of arraylists - how can you sort against an object?

"natural order" requires that the to-be-sorted elements in the List have
the Comparable interface implemented. If you use ArrayLists as elements
in the List you are out of luck, since ArrayList does not implement the
interface. Prepare for getting a ClassCastException.


/Thomas

 

[Roedy Green]

If I use Collections.sort(arraylist), the elements in the arraylist will be
sorted by natural order. What happens when the arraylist is actually an
arraylist of arraylists - how can you sort against an object?

you need to write a Comparator that compares entire ArrayLists in some
way e..g by number of elements.

see http://mindprod.com/jgloss/comparator.html

 

[Roedy Green]

If you use ArrayLists as elements
in the List you are out of luck, since ArrayList does not implement the
interface. Prepare for getting a ClassCastException.

you would have to extend your ArrayList and have it implement
Comparable and write some Comparators.

 

[Viator]

Or extend ArrayList to impelemnt Comparable interface to get the
desired behavior.

Amit

 

[Bruce Lee]

thanks a lot

 

[Thomas Hawtin]

"natural order" requires that the to-be-sorted elements in the List have
the Comparable interface implemented. If you use ArrayLists as elements
in the List you are out of luck, since ArrayList does not implement the
interface. Prepare for getting a ClassCastException.

Or compilation errors in current Java.

Tom Hawtin