How to convert a Java 8 Stream to an Array

Question

What is the easiest shortest way to convert a Java 8 Stream into an array

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If you want to get an array of ints  with values from 1 to 10  from a Stream lt Integer gt   there is IntStream at your disposal  Here we create a Stream with a Stream of method and convert a Stream lt Integer gt  to an IntStream using a mapToInt  Then we can call IntStream s toArray method  Stream lt Integer gt  stream   Stream of 1 2 3 4 5 6 7 8 9 10     or use this to create our stream    Stream lt Integer gt  stream   IntStream rangeClosed 1  10  boxed    int   array    stream mapToInt x - gt  x  toArray     Here is the same thing  without the Stream lt Integer gt   using only the IntStream  int  array2    IntStream rangeClosed 1  10  toArray

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Convert text to string array where separating each value by comma  and trim every field  for example   String   stringArray   Arrays stream line split       map String  trim  toArray String    new

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You can convert a java 8 stream to an array using this simple code block    String   myNewArray3   myNewStream toArray String    new     But let s explain things more  first  let s  Create a list of string filled with three values   String   stringList     Bachiri   Taoufiq   Abderrahman      Create a stream from the given Array    Stream lt String gt  stringStream   Arrays stream stringList     we can now perform some operations on this stream Ex   Stream lt String gt  myNewStream   stringStream map s - gt  s toUpperCase       and finally convert it to a java 8 Array using these methods   1-Classic method  Functional interface   IntFunction lt String   gt  intFunction   new IntFunction lt String   gt           Override     public String   apply int value            return new String value              String   myNewArray   myNewStream toArray intFunction     2 -Lambda expression   String   myNewArray2   myNewStream toArray value - gt  new String value      3- Method reference  String   myNewArray3   myNewStream toArray String    new     Method reference Explanation   It s another way of writing a lambda expression that it s strictly equivalent to the other

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import java util List  import java util stream Stream   class Main        public static void main String   args               Create a stream of strings from list of strings         Stream lt String gt  myStreamOfStrings   List of  lala    foo    bar   stream                Convert stream to array by using toArray method         String   myArrayOfStrings   myStreamOfStrings toArray String    new               Print results         for  String string   myArrayOfStrings                System out println string                       Try it out online  https   repl it  SmaMa Stream-to-array

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You can create a custom collector that convert a stream to array    public static  lt T gt  Collector lt T     T   gt  toArray  IntFunction lt T   gt  converter         return Collectors collectingAndThen                     Collectors toList                       list - gt list toArray  converter apply  list size              and a quick use  List lt String gt  input   Arrays asList            String   result   input stream              collect  CustomCollectors   toArray    String    new

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The easiest method is to use the toArray IntFunction lt A   gt  generator  method with an array constructor reference  This is suggested in the API documentation for the method   String   stringArray   stringStream toArray String    new     What it does is find a method that takes in an integer  the size  as argument  and returns a String    which is exactly what  one of the overloads of  new String   does   You could also write your own IntFunction   Stream lt String gt  stringStream        String   stringArray   stringStream toArray size - gt  new String size      The purpose of the IntFunction lt A   gt  generator is to convert an integer  the size of the array  to a new array   Example code   Stream lt String gt  stringStream   Stream of  a    b    c    String   stringArray   stringStream toArray size - gt  new String size    Arrays stream stringArray  forEach System out  println     Prints   a b c

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Using the toArray IntFunction lt A   gt  generator  method is indeed a very elegant and safe way to convert  or more correctly  collect  a Stream into an array of the same type of the Stream   However  if the returned array s type is not important  simply using the toArray   method is both easier and shorter  For example       Stream lt Object gt  args   Stream of BigDecimal ONE   Two   3       System out printf   s   s   s    args toArray

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you can use the collector like this   Stream lt String gt  io   Stream of  quot foo quot     quot lan quot     quot mql quot      io collect Collectors toCollection ArrayList lt String gt   new

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Stream lt Integer gt  stream   Stream of 1  2  3  4  5  6    int   arr    stream mapToInt x- gt x intValue    toArray

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You can do it in a few ways All the ways are technically the same but using Lambda would simplify some of the code  Lets say we initialize a List first with String  call it persons   List lt String gt  persons   new ArrayList lt String gt     add  a    add  b    add  c       Stream lt String gt  stream   persons stream      Now you can use either of the following ways    Using the Lambda Expresiion to create a new StringArray with defined size   String   stringArray   stream toArray size- new String size    Using the method reference directly   String   stringArray   stream toArray String    new

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Stream lt Integer gt  stream   Stream of 1  2  3  4  5  6         Integer   integers   stream toArray it- gt new Integer it

[java] How to convert a Java 8 Stream to an Array?

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