Converting ArrayList into TreeSet

Question

I have an ArrayList<Card> cards = new ArrayList<Card> which I need to convert into TreeSet<Card>. For this purpose I do:

new TreeSet<Card>(cards)

After all I have a size of the TreeSet equal to 1. The Card class implements Comparable interface. What I'm doing wrong or not doing?

OldCurmudgeon · Accepted Answer · 2013-04-25 14:30:43Z

7

If all of the Cards in the ArrayList evaluate to equal using the provided Comparable interface (i.e. compare always returns 0) then you will end up with just one entry in your TreeSet.

answered Apr 25, 2013 at 14:30

OldCurmudgeon

66.1k18 gold badges126 silver badges220 bronze badges

Sign up to request clarification or add additional context in comments.

1 Comment

Dmitry Stolbov Over a year ago

This solution works. Check this operation Card.compareTo(Card card)

GeertPt · Accepted Answer · 2013-04-25 14:31:50Z

2

They implement Comparable, but how? In a TreeSet, elements for which a.compareTo(b) returns 0, only the first is added.

answered Apr 25, 2013 at 14:31

GeertPt

18k3 gold badges44 silver badges67 bronze badges

2 Comments

OldCurmudgeon Over a year ago

More likely only the last will be retained but that is just pedantry on my part.

GeertPt Over a year ago

@OldCurmudgeon just for pedantry, I tried: Long a = Long.valueOf(123456789012345L); Long b = Long.valueOf(123456789012345L); assertNotSame(a,b); TreeSet<Long> s = new TreeSet<>(Arrays.asList(a,b)); assertEquals(1, s.size()); assertSame(a,s.first());

sarath · Accepted Answer · 2016-11-03 10:03:23Z

-1

Easiest way to convert a List to a Set? - Java

Set<Foo> foo = new HashSet<Foo>(myList);

TreeSet tSet = new TreeSet(myList);

edited Nov 3, 2016 at 10:03

answered Aug 21, 2014 at 4:14

sarath

90313 silver badges20 bronze badges

2 Comments

Christian Kellner Over a year ago

it's about a Treeset, not a HashSet.

sarath Over a year ago

Pass the ArrayList to Treeset. There is a constructor in Treeset that accept Collection.

Collectives™ on Stack Overflow

Converting ArrayList into TreeSet

3 Answers 3

1 Comment

2 Comments

2 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

1 Comment

2 Comments

2 Comments

Your Answer

Sign up or log in

Post as a guest

Related