Convert list to array in Java

Question

How can I convert a List to an Array in Java   Check the code below   ArrayList lt Tienda gt  tiendas  List lt Tienda gt  tiendasList   tiendas   new ArrayList lt Tienda gt      Resources res   this getBaseContext   getResources    XMLParser saxparser    new XMLParser marca res    tiendasList   saxparser parse marca res   tiendas   tiendasList toArray     this adaptador   new adaptadorMarca this  R layout filamarca  tiendas   setListAdapter this adaptador       I need to populate the array tiendas with the values of tiendasList

User · Answer

Try this   List list   new ArrayList    list add  Apple    list add  Banana     Object   ol   list toArray

User · Answer

For ArrayList the following works   ArrayList lt Foo gt  list   new ArrayList lt Foo gt            add values  Foo   resultArray   new Foo list size     resultArray   list toArray resultArray

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Example taken from this page  http   www java-examples com copy-all-elements-java-arraylist-object-array-example  import java util ArrayList   public class CopyElementsOfArrayListToArrayExample      public static void main String   args          create an ArrayList object     ArrayList arrayList   new ArrayList           Add elements to ArrayList     arrayList add  1        arrayList add  2        arrayList add  3        arrayList add  4        arrayList add  5                  To copy all elements of java ArrayList object into array use       Object   toArray   method              Object   objArray   arrayList toArray           display contents of Object array     System out println  ArrayList elements are copied into an Array                                                    Now Array Contains          for int index 0  index  lt  objArray length   index          System out println objArray index              Output would be ArrayList elements are copied into an Array  Now Array Contains   1 2 3 4 5

User · Answer

Best thing I came up without Java 8 was    public static  lt T gt  T   toArray List lt T gt  list  Class lt T gt  objectClass        if  list    null            return null             T   listAsArray    T    Array newInstance objectClass  list size         list toArray listAsArray       return listAsArray      If anyone has a better way to do this  please share

User · Answer

I think this is the simplest way   Foo   array   list toArray new Foo 0

User · Answer

Either   Foo   array   list toArray new Foo 0      or   Foo   array   new Foo list size     list toArray array      fill the array     Note that this works only for arrays of reference types  For arrays of primitive types  use the traditional way   List lt Integer gt  list        int   array   new int list size     for int i   0  i  lt  list size    i    array i    list get i       Update   It is recommended now to use list toArray new Foo 0     not list toArray new Foo list size        From JetBrains Intellij Idea inspection      There are two styles to convert a collection to an array  either using   a pre-sized array  like c toArray new String c size      or   using an empty array  like c toArray new String 0       In   older Java versions using pre-sized array was recommended  as the   reflection   call which is necessary to create an array of proper size   was quite slow    However since late updates of OpenJDK 6 this call   was intrinsified  making   the performance of the empty array version   the same and sometimes even better  compared   to the pre-sized   version  Also passing pre-sized array is dangerous for a concurrent or   synchronized collection as a data race is possible between the   size and toArray   call which may result in extra nulls   at the end of the array  if the collection was concurrently   shrunk   during the operation      This inspection allows to follow the   uniform style  either using an empty array    which is recommended in   modern Java    or using a pre-sized array  which might be faster in   older Java versions or non-HotSpot based JVMs

User · Answer

This  Ondrej s answer    Foo   array   list toArray new Foo 0      Is the most common idiom I see  Those who are suggesting that you use the actual list size instead of  0  are misunderstanding what s happening here   The toArray call does not care about the size or contents of the given array - it only needs its type  It would have been better if it took an actual Type in which case  Foo class  would have been a lot clearer  Yes  this idiom generates a dummy object  but including the list size just means that you generate a larger dummy object   Again  the object is not used in any way  it s only the type that s needed

User · Answer

You can use toArray   api as follows   ArrayList lt String gt  stringList   new ArrayList lt String gt     stringList add  ListItem1    stringList add  ListItem2    String   stringArray   new String stringList size     stringArray   stringList toArray stringList     Values from the array are   for String value   stringList        System out println value

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I came across this code snippet that solves it     Creating a sample ArrayList  List lt Long gt  list   new ArrayList lt Long gt        Adding some long type values list add 100l   list add 200l   list add 300l      Converting the ArrayList to a Long Long   array    Long    list toArray new Long list size         Printing the results System out println array 0          array 1          array 2      The conversion works as follows     It creates a new Long array  with the size of the original list It converts the original ArrayList to an array using the newly created one It casts that array into a Long array  Long     which I appropriately named  array

User · Answer

This is works  Kind of   public static Object   toArray List lt   gt  a        Object   arr   new Object a size         for  int i   0  i  lt  a size    i            arr i    a get i       return arr      Then the main method   public static void main String   args        List lt String gt  list   new ArrayList lt String gt               add  hello            add  world                Object   arr   toArray list       System out println arr 0

User · Answer

An alternative in Java 8  String   strings   list stream   toArray String    new    Since Java 11  String   strings   list toArray String    new

[java] Convert list to array in Java

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