How to get the last value of an ArrayList

Question

How can I get the last value of an ArrayList   I don t know the last index of the ArrayList

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This worked for me  private ArrayList lt String gt  meals  public String take      return meals remove meals size  -1

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this should do it   if  arrayList    null  amp  amp   arrayList isEmpty        T item   arrayList get arrayList size  -1

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If you modify your list  then use listIterator   and iterate from last index  that is size  -1 respectively   If you fail again  check your list structure

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There is no elegant way of getting the last element of a list in Java  compared to e g  items -1  in Python    You have to use list get list size  -1    When working with lists obtained by complicated method calls  the workaround lies in temporary variable   List lt E gt  list   someObject someMethod someArgument  anotherObject anotherMethod     return list get list size  -1     This is the only option to avoid ugly and often expensive or even not working version   return someObject someMethod someArgument  anotherObject anotherMethod    get      someObject someMethod someArgument  anotherObject anotherMethod    size   - 1      It would be nice if fix for this design flaw was introduced to Java API

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In Kotlin  you can use the method last    val lastItem   list last

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Alternative using the Stream API   list stream   reduce  first  second  - gt  second    Results in an Optional of the last element

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Using lambdas   Function lt ArrayList lt T gt   T gt  getLast   a - gt  a get a size   - 1

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All you need to do is use size   to get the last value of the Arraylist   For ex  if you ArrayList of integers  then to get last value you will have to  int lastValue   arrList get arrList size  -1     Remember  elements in an Arraylist can be accessed using index values  Therefore  ArrayLists are generally used to search items

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The size   method returns the number of elements in the ArrayList   The index values of the elements are 0 through  size  -1   so you would use myArrayList get myArrayList size  -1  to retrieve the last element

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As stated in the solution  if the List is empty then an IndexOutOfBoundsException is thrown   A better solution is to use the Optional type   public class ListUtils       public static  lt T gt  Optional lt T gt  last List lt T gt  list            return list isEmpty     Optional empty     Optional of list get list size   - 1              As you d expect  the last element of the list is returned as an Optional   var list   List of 10  20  30   assert ListUtils last list  orElse -1     30    It also deals gracefully with empty lists as well   var emptyList   List  lt Integer gt of    assert ListUtils last emptyList  orElse -1     -1

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There isn t an elegant way in vanilla Java   Google Guava  The Google Guava library is great - check out their Iterables class  This method will throw a NoSuchElementException if the list is empty  as opposed to an IndexOutOfBoundsException  as with the typical size  -1 approach - I find a NoSuchElementException much nicer  or the ability to specify a default   lastElement   Iterables getLast iterableList     You can also provide a default value if the list is empty  instead of an exception   lastElement   Iterables getLast iterableList  null     or  if you re using Options   lastElementRaw   Iterables getLast iterableList  null   lastElement    lastElementRaw    null    Option none     Option some lastElementRaw

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If you use a LinkedList instead   you can access the first element and the last one with just getFirst   and getLast    if you want a cleaner way than size   -1 and get 0    Implementation  Declare a LinkedList  LinkedList lt Object gt  mLinkedList   new LinkedList lt  gt       Then this are the methods you can use to get what you want  in this case we are talking about FIRST and LAST element of a list             Returns the first element in this list                 return the first element in this list         throws NoSuchElementException if this list is empty             public E getFirst             final Node lt E gt  f   first          if  f    null              throw new NoSuchElementException            return f item                        Returns the last element in this list                 return the last element in this list         throws NoSuchElementException if this list is empty             public E getLast             final Node lt E gt  l   last          if  l    null              throw new NoSuchElementException            return l item                        Removes and returns the first element from this list                 return the first element from this list         throws NoSuchElementException if this list is empty             public E removeFirst             final Node lt E gt  f   first          if  f    null              throw new NoSuchElementException            return unlinkFirst f                         Removes and returns the last element from this list                 return the last element from this list         throws NoSuchElementException if this list is empty             public E removeLast             final Node lt E gt  l   last          if  l    null              throw new NoSuchElementException            return unlinkLast l                         Inserts the specified element at the beginning of this list                 param e the element to add             public void addFirst E e            linkFirst e                         Appends the specified element to the end of this list                 lt p gt This method is equivalent to   link  add                  param e the element to add             public void addLast E e            linkLast e           So   then you can use   mLinkedList getLast       to get the last element of the list

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arrays store their size in a local variable called  length    Given an array named  a  you could use the following to reference the last index without knowing the index value  a a length-1   to assign a value of 5 to this last index you would use   a a length-1  5

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I use micro-util class for getting last  and first  element of list   public final class Lists        private Lists                public static  lt T gt  T getFirst List lt T gt  list            return list    null  amp  amp   list isEmpty     list get 0    null             public static  lt T gt  T getLast List lt T gt  list            return list    null  amp  amp   list isEmpty     list get list size   - 1    null              Slightly more flexible   import java util List          Convenience class that provides a clearer API for obtaining list elements      public final class Lists      private Lists                     Returns the first item in the given list  or null if not found             param  lt T gt  The generic list type        param list The list that may have a first item             return null if the list is null or there is no first item          public static  lt T gt  T getFirst  final List lt T gt  list         return getFirst  list  null                    Returns the last item in the given list  or null if not found             param  lt T gt  The generic list type        param list The list that may have a last item             return null if the list is null or there is no last item          public static  lt T gt  T getLast  final List lt T gt  list         return getLast  list  null                    Returns the first item in the given list  or t if not found             param  lt T gt  The generic list type        param list The list that may have a first item        param t The default return value             return null if the list is null or there is no first item          public static  lt T gt  T getFirst  final List lt T gt  list  final T t         return isEmpty  list     t   list get  0                    Returns the last item in the given list  or t if not found             param  lt T gt  The generic list type        param list The list that may have a last item        param t The default return value             return null if the list is null or there is no last item          public static  lt T gt  T getLast  final List lt T gt  list  final T t         return isEmpty  list     t   list get  list size   - 1                    Returns true if the given list is null or empty             param  lt T gt  The generic list type        param list The list that has a last item             return true The list is empty          public static  lt T gt  boolean isEmpty  final List lt T gt  list         return list    null    list isEmpty

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If you can  swap out the ArrayList for an ArrayDeque  which has convenient methods like removeLast

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How about this   Somewhere in your class     List lt E gt  list   new ArrayList lt E gt     private int i   -1      public void addObjToList E elt           i            list add elt               public E getObjFromList            if i    -1                  If list is empty handle the way you would like to    I am returning a null object             return null     or throw an exception                    E object   list get i           list remove i     Optional - makes list work like a stack         i--               Optional - makes list work like a stack         return object

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The following is part of the List interface  which ArrayList implements    E e   list get list size   - 1     E is the element type  If the list is empty  get throws an IndexOutOfBoundsException  You can find the whole API documentation here

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The last item in the list is list size   - 1  The collection is backed by an array and arrays start at index 0   So element 1 in the list is at index 0 in the array   Element 2 in the list is at index 1 in the array  Element 3 in the list is at index 2 in the array   and so on

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guava provides another way to obtain the last element from a List   last   Lists reverse list  get 0   if the provided list is empty it throws an IndexOutOfBoundsException

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A one liner that takes into account empty lists would be  T lastItem   list size      0   null   list get list size   - 1    Or if you don t like null values  and performance isn t an issue   Optional lt T gt  lastItem   list stream   reduce  first  second  - gt  second

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In case you have a spring project  you can also use the CollectionUtils lastElement from Spring  javadoc  and you don t need to add an extra dependency like Google Guave if you didn t need to before  It is null-safe so if you pass null  you will simply receive null in return  Be careful when handling the response though  Here are somes unit test to demonstrate them   Test void lastElementOfList         var names   List of  quot John quot    quot Jane quot         var lastName   CollectionUtils lastElement names        then lastName           as  quot Expected Jane to be the last name in the list quot            isEqualTo  quot Jane quot        Test void lastElementOfSet         var names   new TreeSet lt  gt  Set of  quot Jane quot    quot John quot    quot James quot          var lastName   CollectionUtils lastElement names        then lastName           as  quot Expected John to be the last name in the list quot            isEqualTo  quot John quot       Note  org assertj core api BDDAssertions then java lang String  is used for assertions

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Since the indexing in ArrayList starts from 0 and ends one place before the actual size hence the correct statement to return the last arraylist element would be   int last   mylist get mylist size  -1    For example   if size of array list is 5  then size-1   4 would return the last array element

[java] How to get the last value of an ArrayList

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