Convert an ArrayList to an object array

Question

Is there a command in java for conversion of an ArrayList into a object array  I know how to do this copying each object from the arrayList into the object array  but I was wondering if would it be done automatically   I want something like this   ArrayList lt TypeA gt  a      Let s imagine  a  was filled with TypeA objects  TypeA   array   MagicalCommand a

User · Answer

Yes  ArrayList has a toArray   method   http   java sun com javase 6 docs api java util ArrayList html

User · Answer

Something like the standard Collection toArray T    should do what you need  note that ArrayList implements Collection    TypeA   array   a toArray new TypeA a size        On a side note  you should consider defining a to be of type List lt TypeA gt  rather than ArrayList lt TypeA gt   this avoid some implementation specific definition that may not really be applicable for your application   Also  please see this question about the use of a size   instead of 0 as the size of the array passed to a toArray TypeA

User · Answer

Using these libraries   gson-2 8 5 jar json-20180813 jar  Using this code  List lt Object   gt  testNovedads   crudService createNativeQuery                   quot SELECT cantidad  id FROM NOVEDADES GROUP BY id  quot             Gson gson   new Gson            String json   gson toJson new TestNovedad             JSONObject jsonObject   new JSONObject json           Collection lt TestNovedad gt  novedads   new ArrayList lt  gt             for  Object   object   testNovedads                Iterator lt String gt  iterator   jsonObject keys                int pos   0              for  Iterator i   iterator  i hasNext                       jsonObject put  String  i next    object pos                                novedads add gson fromJson jsonObject toString    TestNovedad class                      for  TestNovedad testNovedad   novedads                System out println testNovedad toString                        Autores  Chalo Mejia     Fecha  01 10 2020     package org main   import java io Serializable   public class TestNovedad implements Serializable        private static final long serialVersionUID   -6362794385792247263L       private int id       private int cantidad       public TestNovedad                TODO Auto-generated constructor stub            public int getId             return id             public void setId int id            this id   id             public int getCantidad             return cantidad             public void setCantidad int cantidad            this cantidad   cantidad              Override     public String toString             return  quot TestNovedad  id  quot    id    quot   cantidad  quot    cantidad    quot   quot

User · Answer

TypeA   array    TypeA    a toArray

User · Answer

Convert an ArrayList to an object   array   ArrayList has a constructor that takes a Collection  so the common  idiom is   List lt T gt  list   new ArrayList lt T gt  Arrays asList array      Which constructs a copy of the list created by the array   now  Arrays asList array  will wrap the array  so changes to the list  will affect the array  and visa versa  Although you can t add or remove   elements from such a list

User · Answer

You can use this code   ArrayList lt TypeA gt  a   new ArrayList lt TypeA gt     Object   o   a toArray      Then if you want that to get that object back into TypeA just check it with instanceOf method

[java] Convert an ArrayList to an object array

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