java- reset list iterator to first element of the list

Question

I need to know how to  reset  LinkedList iterator to its first element   For example   LinkedList lt String gt  list   Iterator iter list listIterator   iter next     iter next     Over and over again and after many moves of the iterator  I need to  reset  the position of iterator     I want to ask how I can  reset  my iterator to first element  I know that I can get list iterator of the first element in this way   iter  list listIterator 1    Is this the best solution  or maybe I missed something in Oracle docs

User · Answer

Calling iterator   on a Collection impl  probably would get a new Iterator on each call   Thus  you can simply call iterator   again to get a new one     Code  IteratorLearn java  import org testng Assert  import org testng annotations Test   import java util Collection  import java util HashSet  import java util Iterator          Iterator learn         author eric     date 12 30 18 4 03 PM     public class IteratorLearn        Test     public void test             Collection lt Integer gt  c   new HashSet lt  gt             for  int i   0  i  lt  10  i                  c add i                      Iterator it              iterate          it   c iterator            System out println   niterate             while  it hasNext                  System out printf   t d n   it next                       Assert assertFalse it hasNext                 consume          it   c iterator            System out println   nconsume elements             it forEachRemaining ele - gt  System out printf   t d n   ele            Assert assertFalse it hasNext               Output   iterate      0     1     2     3     4     5     6     7     8     9  consume elements      0     1     2     3     4     5     6     7     8     9

User · Answer

Best would be not using LinkedList at all  usually it is slower in all disciplines  and less handy   When mainly inserting deleting to the front  especially for big arrays LinkedList is faster   Use ArrayList  and iterate with   int len   list size    for  int i   0  i  lt  len  i        Element ele   list get i       Reset is trivial  just loop again  If you insist on using an iterator   then you have to use a new iterator   iter   list listIterator       I saw only once in my life an advantage of LinkedList  i could loop through whith a while loop and remove the first element

User · Answer

This is an alternative solution  but one could argue it doesn t add enough value to make it worth it   import com google common collect Iterables      Iterator lt String gt  iter   Iterables cycle list  iterator    if iter hasNext          str   iter next        Calling hasNext   will reset the iterator cursor to the beginning if it s a the end

User · Answer

You can call listIterator method again to get an instance of iterator pointing at beginning of list   iter   list listIterator

User · Answer

What you may actually want to use is an Iterable that can return a fresh Iterator multiple times by calling iterator       A function that needs to iterate multiple times can be given one Iterable  public void func Iterable lt Type gt  ible        Iterator lt Type gt  it   ible iterator      Gets an iterator     while  it hasNext              it next              it   ible iterator      Gets a NEW iterator  also from the beginning     while  it hasNext              it next              You must define what the iterator   method does just once beforehand   void main         LinkedList lt String gt  list    This could be any type of object that has an iterator       Define an Iterable that knows how to retrieve a fresh iterator     Iterable lt Type gt  ible   new Iterable lt Type gt               Override         public Iterator lt Type gt  iterator                 return list listIterator      Define how to get a fresh iterator from any object                        Now with a single instance of an Iterable      func ible     you can iterate through it multiple times

User · Answer

If the order doesn t matter  we can re-iterate backward with the same iterator using the hasPrevious   and previous   methods     ListIterator lt T gt  lit   myList listIterator       create just one iterator   Initially the iterator sits at the beginning  we do forward iteration   while  lit hasNext    process lit next        begin - gt  end   Then the iterator sits at the end  we can do backward iteration   while  lit hasPrevious    process2 lit previous        end - gt  begin

[java] java- reset list iterator to first element of the list

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