Create a List of primitive int

Question

Is there a way to create a list of primitive int or any primitives in java like following    List lt int gt  myList   new ArrayList lt int gt       It seems I can do List myList   new ArrayList     and add  int  into this list  But then this would mean I can add anything into this list    Is my only option  creating an array of int and converting it into a list or creating a list of Integer objects

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Java Collection should be collections of Object only.

List<Integer> integerList = new ArrayList<Integer>();

Integer is wrapper class of primitive data type int.

more from JAVA wrapper classes here!

U can directly save and get int to/from integerList as, integerList.add(intValue); int intValue = integerList.get(i)

User · Answer

This is not possible  The java specification forbids the use of primitives in generics  However  you can create ArrayList lt Integer gt  and call add i  if i is an int thanks to boxing

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Is there a way to create a list of primitive int or any primitives in java   No you can t  You can only create List of reference types  like Integer  String  or your custom type      It seems I can do List myList   new ArrayList    and add  int  into this list    When you add int to this list  it is automatically boxed to Integer wrapper type  But it is a bad idea to use raw type lists  or for any generic type for that matter  in newer code      I can add anything into this list     Of course  that is the dis-advantage of using raw type  You can have Cat  Dog  Tiger  Dinosaur  all in one container      Is my only option  creating an array of int and converting it into a list   In that case also  you will get a List lt Integer gt  only  There is no way you can create List lt int gt  or any primitives   You shouldn t be bothered anyways  Even in List lt Integer gt  you can add an int primitive types  It will be automatically boxed  as in below example   List lt Integer gt  list   new ArrayList lt Integer gt     list add 5

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Is there a way to convert an Integer   array to an int   array    This gross omission from the Java core libraries seems to come up on pretty much every project I ever work on  And as convenient as the Trove library might be  I am unable to parse the precise requirements to meet LPGL for an Android app that statically links an LGPL library  preamble says ok  body does not seem to say the same   And it s just plain inconvenient to go rip-and-stripping Apache sources to get these classes  There has to be a better way

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No there isn t any collection that can contain primitive types when Java Collection Framework is being used   However  there are other java collections which support primitive types  such as  Trove  Colt  Fastutil  Guava  An example of how an arraylist with ints would be when Trove Library used is the following    TIntArrayList list  new TIntArrayList      The performance of this list  when compared with the ArrayList of Integers from Java Collections is much better as the autoboxing unboxing to the corresponding Integer Wrapper Class is not needed

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You can use primitive collections available in Eclipse Collections  Eclipse Collections has List  Set  Bag and Map for all primitives  The elements in the primitive collections are maintained as primitives and no boxing takes place   You can initialize a IntList like this   MutableIntList ints   IntLists mutable empty      You can convert from a List lt Integer gt  to IntList like this   List lt Integer gt  integers   new ArrayList lt  gt     MutableIntList ints   ListAdapter adapt integers  collectInt each - gt  each     Note  I am a contributor to Eclipse Collections

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Collections use generics which support either reference types or wilcards  You can however use an Integer wrapper  List lt Integer gt  list   new ArrayList lt  gt

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Try using the ArrayIntList from the apache framework  It works exactly like an arraylist  except it can hold primitive int    More details here -  https   commons apache org dormant commons-primitives apidocs org apache commons collections primitives ArrayIntList html

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When you use Java for Android development  it is recommended to use SparseIntArray to prevent autoboxing between int and Integer   You can finde more information to SparseIntArray in the Android Developers documentation and a good explanation for autoboxing on Android enter link description here

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In Java the type of any variable is either a primitive type or a reference type  Generic type arguments must be reference types  Since primitives do not extend Object they cannot be used as generic type arguments for a parametrized type   Instead use the Integer class which is a wrapper for int   List lt Integer gt  list   new ArrayList lt Integer gt       If your using Java 7 you can simplify this declaration using the diamond operator   List lt Integer gt  list   new ArrayList lt  gt       With autoboxing in Java the primitive type int will become an Integer when necessary        Autoboxing is the automatic conversion that the Java compiler makes   between the primitive types and their corresponding object wrapper   classes    So the following is valid   int myInt   1  List lt Integer gt  list   new ArrayList lt Integer gt     list add myInt    System out println list get 0      prints 1

[java] Create a List of primitive int?

Integer is wrapper class of primitive data type int.

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