Java get last element of a collection

Question

I have a collection  I want to get the last element of the collection  What s the most straighforward and fast way to do so   One solution is to first toArray    and then return the last element of the array  Is there any other better ones

User · Answer

There isn t a last   or first   method in a Collection interface  For getting the last method  you can either do get size   - 1  on a List or reverse the List and do get 0   I don t see a need to have last   method in any Collection API unless you are dealing with Stacks or Queues

User · Answer

A Collection is not a necessarily ordered set of elements so there may not be a concept of the  last  element   If you want something that s ordered  you can use a SortedSet which has a last   method   Or you can use a List and call mylist get mylist size  -1    If you really need the last element you should use a List or a SortedSet   But if all you have is a Collection and you really  really  really need the last element  you could use toArray   or you could use an Iterator and iterate to the end of the list     For example   public Object getLastElement final Collection c        final Iterator itr   c iterator        Object lastElement   itr next        while itr hasNext              lastElement   itr next              return lastElement

User · Answer

It is not very efficient solution  but working one   public static  lt T gt  T getFirstElement final Iterable lt T gt  elements        return elements iterator   next       public static  lt T gt  T getLastElement final Iterable lt T gt  elements        T lastElement   null       for  T element   elements            lastElement   element             return lastElement

User · Answer

Iterables getLast from Google Guava  It has some optimization for Lists and SortedSets too

User · Answer

A reasonable solution would be to use an iterator if you don t know anything about the underlying Collection  but do know that there is a  last  element  This isn t always the case  not all Collections are ordered   Object lastElement   null   for  Iterator collectionItr   c iterator    collectionItr hasNext          lastElement   collectionItr next

User · Answer

If you have Iterable convert to stream and find last element    Iterator lt String gt  sourceIterator   Arrays asList  one    two    three   iterator      Iterable lt String gt  iterable      - gt  sourceIterator     String last   StreamSupport stream iterable spliterator    false  reduce  first  second  - gt  second  orElse null

User · Answer

Well one solution could be   list get list size  -1    Edit  You have to convert the collection to a list before maybe like this  new ArrayList coll

User · Answer

Or you can use a for-each loop   Collection lt X gt  items        X last   null  for  X x   items  last   x

User · Answer

To avoid some of the problems mentioned above  not robust for nulls etc etc   to get first and last element in a list an approach could be  import java util List   public static final  lt A gt  A getLastElement List lt A gt  list        return list    null   getElement list  list size   - 1    null     public static final  lt A gt  A getFirstElement List lt A gt  list        return list    null   getElement list  0    null        private static final  lt A gt  A getElement List lt A gt  list  int pointer        A res   null      if  list size    gt  0            res   list get pointer                         return res      The convention adopted is that the first last element of an empty list is null

User · Answer

This should work without converting to List Array   collectionName stream   reduce  prev  next  - gt  next  orElse null

[java] Java get last element of a collection

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