Create ArrayList from array

Question

I have an array that is initialized like   Element   array    new Element 1   new Element 2   new Element 3      I would like to convert this array into an object of the ArrayList class   ArrayList lt Element gt  arraylist

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Below code seems nice way of doing this   new ArrayList lt T gt  Arrays asList myArray

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You can do it in java 8 as follows  ArrayList lt Element gt  list    ArrayList lt Element gt  Arrays stream array  collect Collectors toList

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Given Object Array   Element   array    new Element 1   new Element 2   new Element 3    new Element 2      Convert Array to List       List lt Element gt  list   Arrays stream array  collect Collectors toList       Convert Array to ArrayList      ArrayList lt Element gt  arrayList   Arrays stream array                                          collect Collectors toCollection ArrayList  new      Convert Array to LinkedList      LinkedList lt Element gt  linkedList   Arrays stream array                        collect Collectors toCollection LinkedList  new      Print List       list forEach element - gt            System out println element i             OUTPUT  1  2  3

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Another way  although essentially equivalent to the new ArrayList Arrays asList array   solution performance-wise   Collections addAll arraylist  array

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Since this question is pretty old  it surprises me that nobody suggested the simplest form yet   List lt Element gt  arraylist   Arrays asList new Element 1   new Element 2   new Element 3      As of Java 5  Arrays asList   takes a varargs parameter and you don t have to construct the array explicitly

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You probably just need a List  not an ArrayList   In that case you can just do   List lt Element gt  arraylist   Arrays asList array

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Hi you can use this line of code   and it s the simplest way  new ArrayList lt  gt  Arrays asList myArray     or in case you use  Java 9 you can also use this method  List lt String gt  list   List of  quot Hello quot    quot Java quot     List lt Integer gt  list   List of 1  2  3

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You can use the following 3 ways to create ArrayList from Array    String   array     quot a quot    quot b quot    quot c quot    quot d quot    quot e quot         Method 1   List lt String gt  list   Arrays asList array                  Method 2   List lt String gt  list1   new ArrayList lt String gt       Collections addAll list1  array        Method 3   List lt String gt  list2   new ArrayList lt String gt       for String text array         list2 add text

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Since Java 8 there is an easier way to transform   import java util List      import static java util stream Collectors toList   public static  lt T gt  List lt T gt  fromArray T   array        return Arrays stream array  collect toList

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Use the following code to convert an element array into an ArrayList    Element   array    new Element 1   new Element 2   new Element 3     ArrayList lt Element gt elementArray new ArrayList    for int i 0 i lt array length i          elementArray add array i

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Given   Element   array   new Element     new Element 1   new Element 2   new Element 3       The simplest answer is to do   List lt Element gt  list   Arrays asList array     This will work fine   But some caveats    The list returned from asList has fixed size   So  if you want to be able to add or remove elements from the returned list in your code  you ll need to wrap it in a new ArrayList   Otherwise you ll get an UnsupportedOperationException  The list returned from asList   is backed by the original array   If you modify the original array  the list will be modified as well   This may be surprising

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If we see the definition of Arrays asList   method you will get something like this     public static  lt T gt  List lt T gt  asList T    a    varargs are of T type     So  you might initialize arraylist like this     List lt Element gt  arraylist   Arrays asList new Element 1   new Element 2   new Element 3         Note   each new Element int args  will be treated as Individual Object and can be passed as a var-args   There might be another answer for this question too  If you see declaration for java util Collections addAll   method you will get something like this   public static  lt T gt  boolean addAll Collection lt   super T gt  c  T    a     So  this code is also useful to do so  Collections addAll arraylist  array

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Use below script Object   myNum    10  20  30  40   List lt Object gt  newArr   new ArrayList lt  gt  Arrays asList myNum

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You can convert using different methods   List lt Element gt  list   Arrays asList array   List lt Element gt  list   new ArrayList    Collections addAll list  array   Arraylist list   new Arraylist    list addAll Arrays asList array      For more detail you can refer to http   javarevisited blogspot in 2011 06 converting-array-to-arraylist-in-java html

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In Java 9 you can use   List lt String gt  list   List of  Hello    World    from    Java    List lt Integer gt  list   List of 1  2  3  4  5

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Another simple way is to add all elements from the array to a new ArrayList using a for-each loop   ArrayList lt Element gt  list   new ArrayList lt  gt      for Element e   array      list add e

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We can easily convert an array to ArrayList  We use Collection interface s addAll   method for the purpose of copying content from one list to another     Arraylist arr   new Arraylist     arr addAll Arrays asList asset

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In java there are mainly 3 methods to convert an array to an arrayList  Using Arrays asList   method   Pass the required array to this method and get a List object and pass it as a parameter to the constructor of the ArrayList class  List lt String gt  list   Arrays asList array                      System out println list     Collections addAll   method - Create a new list before using this method and then add array elements using this method to existing list   List lt String gt  list1   new ArrayList lt String gt      Collections addAll list1  array    System out println list1     Iteration method - Create a new list  Iterate the array and add each element to the list   List lt String gt  list2   new ArrayList lt String gt      for String text array         list2 add text       System out println list2      you can refer this document too

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There is one more way that you can use to convert the array into an ArrayList  You can iterate over the array and insert each index into the ArrayList and return it back as in ArrayList  This is shown below  public static void main String   args            String   array    new String  quot David quot    new String  quot John quot    new String  quot Mike quot              ArrayList lt String gt  theArrayList   convertToArrayList array              private static ArrayList lt String gt  convertToArrayList String   array            ArrayList lt String gt  convertedArray   new ArrayList lt String gt              for  String element   array                convertedArray add element                      return convertedArray

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You can create an ArrayList using Cactoos  I m one of the developers    List lt String gt  names   new StickyList lt  gt      Scott Fitzgerald    Fyodor Dostoyevsky       There is no guarantee that the object will actually be of class ArrayList  If you need that guarantee  do this   ArrayList lt String gt  list   new ArrayList lt  gt     new StickyList lt  gt        Scott Fitzgerald    Fyodor Dostoyevsky

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According with the question the answer using java 1 7 is   ArrayList lt Element gt  arraylist   new ArrayList lt Element gt  Arrays  lt Element gt asList array      However it s better always use the interface   List lt Element gt  arraylist   Arrays  lt Element gt asList array

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For normal size arrays  above answers hold good  In case you have huge size of array and using java 8  you can do it using stream    Element   array    new Element 1   new Element 2   new Element 3      List lt Element gt  list   Arrays stream array  collect Collectors toList

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new ArrayList lt T gt  Arrays asList myArray      Make sure that myArray is the same type as T  You ll get a compiler error if you try to create a List lt Integer gt  from an array of int  for example

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new ArrayList lt  gt  Arrays asList array

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old thread  but just 2 cents as none mention Guava or other libs and some other details   If You Can  Use Guava  It s worth pointing out the Guava way  which greatly simplifies these shenanigans   Usage  For an Immutable List  Use the ImmutableList class and its of   and copyOf   factory methods  elements can t be null    List lt String gt  il   ImmutableList of  string    elements        from varargs List lt String gt  il   ImmutableList copyOf aStringArray           from array   For A Mutable List  Use the Lists class and its newArrayList   factory methods   List lt String gt  l1   Lists newArrayList anotherListOrCollection         from collection List lt String gt  l2   Lists newArrayList aStringArray                    from array List lt String gt  l3   Lists newArrayList  or    string    elements       from varargs   Please also note the similar methods for other data structures in other classes  for instance in Sets   Why Guava   The main attraction could be to reduce the clutter due to generics for type-safety  as the use of the Guava factory methods allow the types to be inferred most of the time  However  this argument holds less water since Java 7 arrived with the new diamond operator   But it s not the only reason  and Java 7 isn t everywhere yet   the shorthand syntax is also very handy  and the methods initializers  as seen above  allow to write more expressive code  You do in one Guava call what takes 2 with the current Java Collections     If You Can t     For an Immutable List  Use the JDK s Arrays class and its asList   factory method  wrapped with a Collections unmodifiableList     List lt String gt  l1   Collections unmodifiableList Arrays asList anArrayOfElements    List lt String gt  l2   Collections unmodifiableList Arrays asList  element1    element2       Note that the returned type for asList   is a List using a concrete ArrayList implementation  but it is NOT java util ArrayList  It s an inner type  which emulates an ArrayList but actually directly references the passed array and makes it  write through   modifications are reflected in the array    It forbids modifications through some of the List API s methods by way of simply extending an AbstractList  so  adding or removing elements is unsupported   however it allows calls to set   to override elements  Thus this list isn t truly immutable and a call to asList   should be wrapped with Collections unmodifiableList     See the next step if you need a mutable list   For a Mutable List  Same as above  but wrapped with an actual java util ArrayList   List lt String gt  l1    new ArrayList lt String gt  Arrays asList array          Java 1 5 to 1 6 List lt String gt  l1b   new ArrayList lt  gt  Arrays asList array                Java 1 7  List lt String gt  l2    new ArrayList lt String gt  Arrays asList  a    b        Java 1 5 to 1 6 List lt String gt  l2b   new ArrayList lt  gt  Arrays asList  a    b              Java 1 7      For Educational Purposes  The Good ol  Manual Way     for Java 1 5  static  lt T gt  List lt T gt  arrayToList final T   array      final List lt T gt  l   new ArrayList lt T gt  array length      for  final T s   array        l add s         return  l         for Java  lt  1 5  no generics  no compile-time type-safety  boo   static List arrayToList final Object   array      final List l   new ArrayList array length      for  int i   0  i  lt  array length  i          l add array i          return  l

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If you use    new ArrayList lt T gt  Arrays asList myArray      you may create and fill two lists   Filling twice a big list is exactly what you don t want to do because it will create another Object   array each time the capacity needs to be extended   Fortunately the JDK implementation is fast and Arrays asList a    is very well done  It create a kind of ArrayList named Arrays ArrayList where the Object   data points directly to the array      in Arrays  SafeVarargs public static  lt T gt  List lt T gt  asList T    a        return new ArrayList lt  gt  a       still in Arrays  creating a private unseen class private static class ArrayList lt E gt       private final E   a          ArrayList E   array            a   array     you point to the previous array                    The dangerous side is that if you change the initial array  you change the List   Are you sure you want that   Maybe yes  maybe not   If not  the most understandable way is to do this    ArrayList lt Element gt  list   new ArrayList lt Element gt  myArray length      you know the initial capacity for  Element element   myArray        list add element       Or as said  glglgl  you can create another independant ArrayList with    new ArrayList lt T gt  Arrays asList myArray      I love to use Collections  Arrays  or Guava  But if it don t fit  or you don t feel it  just write another inelegant line instead

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Simplest way to do so is by adding following code  Tried and Tested   String   Array1   one   two   three    ArrayList lt String gt  s1  new ArrayList lt String gt  Arrays asList Array1

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You also can do it with stream in Java 8    List lt Element gt  elements   Arrays stream array  collect Collectors toList

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Java 8   s Arrays class provides a stream   method which has overloaded versions accepting both primitive arrays and Object arrays         Converting a Primitive  int  Array to List        int intArray      1  2  3  4  5    List lt Integer gt  integerList1   Arrays stream intArray  boxed   collect Collectors toList             IntStream of  or  Arrays stream  Gives The Same Output        List lt Integer gt  integerList2   IntStream of intArray  boxed   collect Collectors toList            Converting an  Integer  Array to List        Integer integerArray      1  2  3  4  5  6  7  8  9  10    List lt Integer gt  integerList3   Arrays stream integerArray  collect Collectors toList

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Java 9 In Java 9  you can use List of static factory method in order to create a List literal  Something like the following  List lt Element gt  elements   List of new Element 1   new Element 2   new Element 3     This would return an immutable list containing three elements  If you want a mutable list  pass that list to the ArrayList constructor  new ArrayList lt  gt  List of    elements vararg     JEP 269  Convenience Factory Methods for Collections JEP 269 provides some convenience factory methods for Java Collections API  These immutable static factory methods are built into the List  Set  and Map interfaces in Java 9 and later

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Even though there are many perfectly written answers to this question  I will add my inputs    Say you have Element   array     new Element 1   new Element 2   new Element 3      New ArrayList can be created in the following ways  ArrayList lt Element gt  arraylist 1   new ArrayList lt  gt  Arrays asList array    ArrayList lt Element gt  arraylist 2   new ArrayList lt  gt       Arrays asList new Element     new Element 1   new Element 2   new Element 3           Add through a collection ArrayList lt Element gt  arraylist 3   new ArrayList lt  gt     Collections addAll arraylist 3  array     And they very well support all operations of ArrayList  arraylist 1 add new Element 4       or remove    Success arraylist 2 add new Element 4       or remove    Success arraylist 3 add new Element 4       or remove    Success   But the following operations returns just a List view of an ArrayList and not actual ArrayList      Returns a List view of array and not actual ArrayList List lt Element gt  listView 1    List lt Element gt   Arrays asList array   List lt Element gt  listView 2   Arrays asList array   List lt Element gt  listView 3   Arrays asList new Element 1   new Element 2   new Element 3      Therefore  they will give error when trying to make some ArrayList operations  listView 1 add new Element 4       Error listView 2 add new Element 4       Error listView 3 add new Element 4       Error   More on List representation of array link

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There is another option if your goal is to generate a fixed list at runtime  which is as simple as it is effective   static final ArrayList lt Element gt  myList   generateMyList     private static ArrayList lt Element gt  generateMyList       final ArrayList lt Element gt  result   new ArrayList lt  gt       result add new Element 1      result add new Element 2      result add new Element 3      result add new Element 4      return result       The benefit of using this pattern is  that the list is for once generated very intuitively and therefore is very easy to modify even with large lists or complex initialization  while on the other hand always contains the same Elements on every actual run of the program  unless you change it at a later point of course

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the lambda expression that generates a list of type ArrayList lt Element gt   1  without an unchecked cast  2  without creating a second list  with eg  asList     ArrayList lt Element gt  list   Stream of  array   collect  Collectors toCollection  ArrayList  new

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This is the first and the easiest method  new ArrayList lt T gt  Arrays asList myArray      Another method    declare myarray ArrayList  lt String gt  ar   new ArrayList lt String gt      for String s   myArray       ar add s       This is iterating through the array and adding each element separately  The kind of for loop used here is called enhanced for loop

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as all said this will do so    new ArrayList lt  gt  Arrays asList  1   2   3   4       and the common newest way to create array is observableArrays  ObservableList  A list that allows listeners to track changes when they occur   for Java SE you can try   FXCollections observableArrayList new Element 1   new Element 2   new Element 3      that is according to Oracle Docs     observableArrayList     Creates a new empty observable list that is backed by an arraylist    observableArrayList E    items    Creates a new observable array list with items added to it    Update Java 9  also in Java 9 it s a little bit easy   List lt String gt  list   List of  element 1    element 2    element 3

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Another Java8 solution  I may have missed the answer among the large set  If so  my apologies   This creates an ArrayList  as opposed to a List  i e  one can delete elements   package package org something util   import java util ArrayList  import java util Arrays  import java util List  import java util stream Collectors   public class Junk        static  lt T gt  ArrayList lt T gt   arrToArrayList T   arr           return Arrays asList arr               stream                collect Collectors toCollection ArrayList  new               public static void main String   args            String   sArr   new String    Hello    cruel    world            List lt String gt  ret   arrToArrayList sArr              Verify one can remove an item and print list to verify so         ret remove 1           ret stream                forEach System out  println             Output is     Hello  world

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If the array is of a primitive type  the given answers won t work  But since Java 8 you can use   int   array   new int 5   Arrays stream array  boxed   collect Collectors toList

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Use below code  Element   array    new Element 1   new Element 2   new Element 3    ArrayList lt Element gt  list    ArrayList  Arrays asList array

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Guava import com google common collect ListsLists     List lt String gt  list   Lists newArrayList aStringArray

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Already everyone has provided enough good answer for your problem   Now from the all suggestions  you need to decided which will fit your requirement  There are two types of collection which you need to know  One is unmodified collection and other one collection which will allow you to modify the object later   So  Here I will give short example for two use cases    Immutable collection creation    When you don t want to modify the collection object after creation  List lt Element gt  elementList   Arrays asList array  Mutable collection creation    When you may want to modify the created collection object after creation   List lt Element gt  elementList   new ArrayList lt Element gt  Arrays asList array

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Another update  almost ending year 2014  you can do it with Java 8 too   ArrayList lt Element gt  arrayList   Stream of myArray  collect Collectors toCollection ArrayList  new      A few characters would be saved  if this could be just a List   List lt Element gt  list   Stream of myArray  collect Collectors toList

[java] Create ArrayList from array

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