How can I generate a list or array of sequential integers in Java

Question

Is there a short and sweet way to generate a List lt Integer gt   or perhaps an  Integer   or int    with sequential values from some start value to an end value   That is  something shorter than  but equivalent to1 the following   void List lt Integer gt  makeSequence int begin  int end      List lt Integer gt  ret   new ArrayList lt  gt  end - begin   1     for  int i begin  i lt  end  i          ret add i         return ret        The use of guava is fine   Update   Performance Analysis  Since this question has received several good answers  both using native Java 8 and third party libraries  I thought I d test the performance of all the solutions   The first test simply tests creating a list of 10 elements  1  10  using the following methods    classicArrayList  the code given above in my question  and essentially the same as adarshr s answer   eclipseCollections  the code given in Donald s answer below using Eclipse Collections 8 0  guavaRange  the code given in daveb s answer below  Technically  this doesn t create a List lt Integer gt  but rather a ContiguousSet lt Integer gt  - but since it implements Iterable lt Integer gt  in-order  it mostly works for my purposes  intStreamRange  the code given in Vladimir s answer below  which uses IntStream rangeClosed   - which was introduced in Java 8  streamIterate  the code given in Catalin s answer below which also uses IntStream functionality introduced in Java 8    Here are the results in kilo-operations per second  higher numbers are better   for all the above with lists of size 10         and again for lists of size 10 000     That last chart is correct - the solutions other than Eclipse and Guava are too slow to even get a single pixel bar  The fast solutions are 10 000 to 20 000 times faster than the rest   What s going on here  of course  is that the guava and eclipse solutions don t actually materialize any kind of 10 000 element list - they are simply fixed-size wrappers around the start and endpoints  Each element is created as needed during iteration  Since we don t actually iterate in this test  the cost is deferred  All of the other solutions actually materialize the full list in memory and pay a heavy price in a creation-only benchmark   Let s do something a bit more realistic and also iterate over all the integers  summing them  So in the case of the IntStream rangeClosed variant  the benchmark looks like    Benchmark public int intStreamRange         List lt Integer gt  ret   IntStream rangeClosed begin  end  boxed   collect Collectors toList            int total   0      for  int i   ret            total    i            return total        Here  the pictures changes a lot  although the non-materializing solutions are still the fastest  Here s length 10          and length   10 000     The long iteration over many elements evens things up a lot  but eclipse and guava remain more than twice as fast even on the 10 000 element test   So if you really want a List lt Integer gt   eclipse collections seems like the best choice - but of course if you use streams in a more native way  e g   forgetting  boxed   and doing a reduction in the primitive domain  you ll probably end up faster than all these variants      1 Perhaps with the exception of error handling  e g   if end  lt  begin  or if the size exceeds some implementation or JVM limits  e g   arrays larger than 2 31-1

User · Answer

The following one-liner Java 8 version will generate   1  2  3     10    The first arg of iterate is the first nr in the sequence  and the first arg of limit is the last number   List lt Integer gt  numbers   Stream iterate 1  n - gt  n   1                                 limit 10                                 collect Collectors toList

User · Answer

This is the shortest I could get using Core Java   List lt Integer gt  makeSequence int begin  int end      List lt Integer gt  ret   new ArrayList end - begin   1      for int i   begin  i  lt   end  i    ret add i       return ret

User · Answer

You could use Guava Ranges  You can get a SortedSet by using  ImmutableSortedSet lt Integer gt  set   Ranges open 1  5  asSet DiscreteDomains integers        set contains  2  3  4

User · Answer

Well  this one liner might qualify  uses Guava Ranges   ContiguousSet lt Integer gt  integerList   ContiguousSet create Range closedOpen 0  10   DiscreteDomain integers     System out println integerList     This doesn t create a List lt Integer gt   but ContiguousSet offers much the same functionality  in particular implementing Iterable lt Integer gt  which allows foreach implementation in the same way as List lt Integer gt    In older versions  somewhere before Guava 14  you could use this   ImmutableList lt Integer gt  integerList   Ranges closedOpen 0  10  asSet DiscreteDomains integers    asList    System out println integerList     Both produce    0  1  2  3  4  5  6  7  8  9

User · Answer

This is the shortest I could find    List version  public List lt Integer gt  makeSequence int begin  int end        List lt Integer gt  ret   new ArrayList lt Integer gt    end - begin        for    begin  lt  end            ret add begin          return ret      Array Version  public int   makeSequence int begin  int end        if end  lt  begin          return null       int   ret   new int   end - begin       for  int i 0  begin  lt  end            ret i      begin        return ret

User · Answer

This one might works for you      void List lt Integer gt  makeSequence int begin  int end       AtomicInteger ai new AtomicInteger begin     List lt Integer gt  ret   new ArrayList end-begin 1      while   end-- gt begin         ret add ai getAndIncrement            return ret

User · Answer

With Java 8 it is so simple so it doesn t even need separate method anymore   List lt Integer gt  range   IntStream rangeClosed start  end       boxed   collect Collectors toList

User · Answer

You can use the Interval class from Eclipse Collections   List lt Integer gt  range   Interval oneTo 10   range forEach System out  print       prints 12345678910   The Interval class is lazy  so doesn t store all of the values   LazyIterable lt Integer gt  range   Interval oneTo 10   System out println range makeString           prints 1 2 3 4 5 6 7 8 9 10   Your method would be able to be implemented as follows   public List lt Integer gt  makeSequence int begin  int end        return Interval fromTo begin  end       If you would like to avoid boxing ints as Integers  but would still like a list structure as a result  then you can use IntList with IntInterval from Eclipse Collections   public IntList makeSequence int begin  int end        return IntInterval fromTo begin  end       IntList has the methods sum    min    minIfEmpty    max    maxIfEmpty    average   and median   available on the interface   Update for clarity  11 27 2017  An Interval is a List lt Integer gt   but it is lazy and immutable   It is extremely useful for generating test data  especially if you deal a lot with collections   If you want you can easily copy an interval to a List  Set or Bag as follows   Interval integers   Interval oneTo 10   Set lt Integer gt  set   integers toSet    List lt Integer gt  list   integers toList    Bag lt Integer gt  bag   integers toBag      An IntInterval is an ImmutableIntList which extends IntList   It also has converter methods   IntInterval ints   IntInterval oneTo 10   IntSet set   ints toSet    IntList list   ints toList    IntBag bag   ints toBag      An Interval and an IntInterval do not have the same equals contract   Update for Eclipse Collections 9 0  You can now create primitive collections from primitive streams   There are withAll and ofAll methods depending on your preference   If you are curious  I explain why we have both here   These methods exist for mutable and immutable Int Long Double Lists  Sets  Bags and Stacks   Assert assertEquals          IntInterval oneTo 10           IntLists mutable withAll IntStream rangeClosed 1  10      Assert assertEquals          IntInterval oneTo 10           IntLists immutable withAll IntStream rangeClosed 1  10       Note  I am a committer for Eclipse Collections

[java] How can I generate a list or array of sequential integers in Java?

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