How to get a reversed list view on a list in Java

Question

I want to have a reversed list view on a list  in a similar way than List sublist provides a sublist view on a list   Is there some function which provides this functionality   I don t want to make any sort of copy of the list nor modify the list   It would be enough if I could get at least a reverse iterator on a list in this case though     Also  I know how to implement this myself  I m just asking if Java already provides something like this   Demo implementation   static  lt T gt  Iterable lt T gt  iterableReverseList final List lt T gt  l        return new Iterable lt T gt              public Iterator lt T gt  iterator                 return new Iterator lt T gt                      ListIterator lt T gt  listIter   l listIterator l size                                         public boolean hasNext     return listIter hasPrevious                      public T next     return listIter previous                      public void remove     listIter remove                                                             I just have found out that some List implementations have descendingIterator   which is what I need  Though there is no general such implementation for List  Which is kind of strange because the implementation I have seen in LinkedList is general enough to work with any List

User · Answer

If i have understood correct then it is one line of code  It worked for me     Collections reverse yourList

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java util Deque has descendingIterator   - if your List is a Deque  you can use that

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You can also invert the position when you request an object   Object obj   list get list size   - 1 - position

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Use the  clone   method on your List  It will return a shallow copy  meaning that it will contain pointers to the same objects  so you won t have to copy the list  Then just use Collections    Ergo    Collections reverse list clone       If you are using a List and don t have access to clone   you can use subList     List lt   gt  shallowCopy   list subList 0  list size     Collections reverse shallowCopy

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Use reverse      methods of java util Collections class  Pass your list as a parameter and your list will get reversed   Collections reverse list

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Guava provides this  Lists reverse List   List lt String gt  letters   ImmutableList of  a    b    c    List lt String gt  reverseView   Lists reverse letters    System out println reverseView       c  b  a    Unlike Collections reverse  this is purely a view    it doesn t alter the ordering of elements in the original list  Additionally  with an original list that is modifiable  changes to both the original list and the view are reflected in the other

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Its not exactly elegant  but if you use List listIterator int index  you can get a bi-directional ListIterator to the end of the list       Assume List lt String gt  foo  ListIterator li   foo listIterator foo size      while  li hasPrevious         String curr   li previous

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I know this is an old post but today I was looking for something like this  In the end I wrote the code myself   private List reverseList List myList        List invertedList   new ArrayList        for  int i   myList size   - 1  i  gt   0  i--            invertedList add myList get i              return invertedList      Not recommended for long Lists  this is not optimized at all  It s kind of an easy solution for controlled scenarios  the Lists I handle have no more than 100 elements    Hope it helps somebody

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You can also do this    static ArrayList lt String gt  reverseReturn ArrayList lt String gt  alist       if alist  null    alist isEmpty                 return null           ArrayList lt String gt  rlist   new ArrayList lt  gt  alist       Collections reverse rlist      return rlist

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I use this   public class ReversedView lt E gt  extends AbstractList lt E gt        public static  lt E gt  List lt E gt  of List lt E gt  list            return new ReversedView lt  gt  list              private final List lt E gt  backingList       private ReversedView List lt E gt  backingList           this backingList   backingList              Override     public E get int i            return backingList get backingList size  -i-1               Override     public int size             return backingList size               like this   ReversedView of backingList     is a fully-fledged generic  but read-only  list

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For small sized list we can create LinkedList and then can make use of descending iterator as   List lt String gt  stringList   new ArrayList lt  gt  Arrays asList  One    Two    Three     stringList stream   collect Collectors toCollection LinkedList  new             descendingIterator             forEachRemaining System out  println      Three  Two  One System out println stringList      One  Two  Three

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Collections reverse nums      It actually reverse the order of the elements   Below code should be much appreciated -  List lt Integer gt  nums   new ArrayList lt Integer gt     nums add 61   nums add 42   nums add 83   nums add 94   nums add 15     Tosort the collections uncomment the below line   Collections sort nums     Collections reverse nums    System out println nums     Output  15 94 83 42 61

[java] How to get a reversed list view on a list in Java?

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