Does Java SE 8 have Pairs or Tuples

Question

I am playing around with lazy functional operations in Java SE 8  and I want to map an index i to a pair   tuple  i  value i    then filter based on the second value i  element  and finally output just the indices   Must I still suffer this  What is the equivalent of the C   Pair lt L R gt  in Java  in the bold new era of lambdas and streams   Update  I presented a rather simplified example  which has a neat solution offered by  dkatzel in one of the answers below  However  it does not generalize  Therefore  let me add a more general example   package com example test   import java util ArrayList  import java util stream IntStream   public class Main      public static void main String   args        boolean      directed acyclic graph   new boolean               false   true  false   true  false   true            false  false  false   true  false   true            false  false  false   true  false   true            false  false  false  false  false   true            false  false  false  false  false   true            false  false  false  false  false  false              System out println          IntStream range 0  directed acyclic graph length           parallel            mapToLong i - gt  IntStream range 0  directed acyclic graph i  length               filter j - gt  directed acyclic graph j  i                count                      filter n - gt  n    0           collect    - gt  new ArrayList lt Long gt      c  e  - gt  c add e    c1  c2  - gt  c1 addAll c2                   This gives incorrect output of  0  0  0  which corresponds to the counts for the three columns that are all false  What I need are the indices of these three columns  The correct output should be  0  2  4   How can I get this result

User · Answer

Yes   Map Entry can be used as a Pair     Unfortunately it does not help with Java 8 streams as the problem is that even though lambdas can take multiple arguments  the Java language only allows for returning a single value  object or primitive type    This implies that whenever you have a stream you end up with being passed a single object from the previous operation   This is a lack in the Java language  because if multiple return values was supported AND streams supported them we could have much nicer non-trivial tasks done by streams   Until then  there is only little use   EDIT 2018-02-12   While working on a project I wrote a helper class which helps handling the special case of having an identifier earlier in the stream you need at a later time but the stream part in between does not know about it   Until I get around to release it on its own it is available at IdValue java with a unit test at IdValueTest java

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You can have a look on these built-in classes     AbstractMap SimpleEntry AbstractMap SimpleImmutableEntry

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Since Java 9  you can create instances of Map Entry easier than before   Entry lt Integer  String gt  pair   Map entry 1   a      Map entry returns an unmodifiable Entry and forbids nulls

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UPDATE  This answer is in response to the original question  Does Java SE 8 have Pairs or Tuples   And implicitly  if not  why not   The OP has updated the question with a more complete example  but it seems like it can be solved without using any kind of Pair structure   Note from OP  here is the other correct answer      The short answer is no  You either have to roll your own or bring in one of the several libraries that implements it   Having a Pair class in Java SE was proposed and rejected at least once  See this discussion thread on one of the OpenJDK mailing lists  The tradeoffs are not obvious  On the one hand  there are many Pair implementations in other libraries and in application code  That demonstrates a need  and adding such a class to Java SE will increase reuse and sharing  On the other hand  having a Pair class adds to the temptation of creating complicated data structures out of Pairs and collections without creating the necessary types and abstractions   That s a paraphrase of Kevin Bourillion s message from that thread    I recommend everybody read that entire email thread  It s remarkably insightful and has no flamage  It s quite convincing  When it started I thought   Yeah  there should be a Pair class in Java SE  but by the time the thread reached its end I had changed my mind   Note however that JavaFX has the javafx util Pair class  JavaFX s APIs evolved separately from the Java SE APIs   As one can see from the linked question What is the equivalent of the C   Pair in Java  there is quite a large design space surrounding what is apparently such a simple API  Should the objects be immutable  Should they be serializable  Should they be comparable  Should the class be final or not  Should the two elements be ordered  Should it be an interface or a class  Why stop at pairs  Why not triples  quads  or N-tuples   And of course there is the inevitable naming bikeshed for the elements     a  b   first  second   left  right   car  cdr   foo  bar  etc    One big issue that has hardly been mentioned is the relationship of Pairs to primitives  If you have an  int x  int y  datum that represents a point in 2D space  representing this as Pair lt Integer  Integer gt  consumes three objects instead of two 32-bit words  Furthermore  these objects must reside on the heap and will incur GC overhead   It would seem clear that  like Streams  it would be essential for there to be primitive specializations for Pairs  Do we want to see   Pair ObjIntPair ObjLongPair ObjDoublePair IntObjPair IntIntPair IntLongPair IntDoublePair LongObjPair LongIntPair LongLongPair LongDoublePair DoubleObjPair DoubleIntPair DoubleLongPair DoubleDoublePair   Even an IntIntPair would still require one object on the heap   These are  of course  reminiscent of the proliferation of functional interfaces in the java util function package in Java SE 8  If you don t want a bloated API  which ones would you leave out  You could also argue that this isn t enough  and that specializations for  say  Boolean should be added as well   My feeling is that if Java had added a Pair class long ago  it would have been simple  or even simplistic  and it wouldn t have satisfied many of the use cases we are envisioning now  Consider that if Pair had been added in the JDK 1 0 time frame  it probably would have been mutable   Look at java util Date   Would people have been happy with that  My guess is that if there were a Pair class in Java  it would be kinda-sort-not-really-useful and everybody will still be rolling their own to satisfy their needs  there would be various Pair and Tuple implementations in external libraries  and people would still be arguing discussing about how to fix Java s Pair class  In other words  kind of in the same place we re at today   Meanwhile  some work is going on to address the fundamental issue  which is better support in the JVM  and eventually the Java language  for value types  See this State of the Values document  This is preliminary  speculative work  and it covers only issues from the JVM perspective  but it already has a fair amount of thought behind it  Of course there are no guarantees that this will get into Java 9  or ever get in anywhere  but it does show the current direction of thinking on this topic

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Vavr  formerly called Javaslang   http   www vavr io  provides tuples  til size of 8  as well  Here is the javadoc  https   static javadoc io io vavr vavr 0 9 0 io vavr Tuple html    This is a simple example   Tuple2 lt Integer  String gt  entry   Tuple of 1   A     Integer key   entry  1  String value   entry  2    Why JDK itself did not come with a simple kind of tuples til now is a mystery to me  Writing wrapper classes seems to be an every day business

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Sadly  Java 8 did not introduce pairs or tuples  You can always use org apache commons lang3 tuple of course  which personally I do use in combination with Java 8  or you can create your own wrappers  Or use Maps  Or stuff like that  as is explained in the accepted answer to that question you linked to     UPDATE  JDK 14 is introducing records as a preview feature  These aren t tuples  but can be used to save many of the same problems  In your specific example from above  that could look something like this   public class Jdk14Example       record CountForIndex int index  long count          public static void main String   args            boolean      directed acyclic graph   new boolean                       false   true  false   true  false   true                    false  false  false   true  false   true                    false  false  false   true  false   true                    false  false  false  false  false   true                    false  false  false  false  false   true                    false  false  false  false  false  false                      System out println                  IntStream range 0  directed acyclic graph length                           parallel                            mapToObj i - gt                                long count   IntStream range 0  directed acyclic graph i  length                                               filter j - gt  directed acyclic graph j  i                                                count                                return new CountForIndex i  count                                                                                filter n - gt  n count    0                           collect    - gt  new ArrayList lt CountForIndex gt      c  e  - gt  c add e    c1  c2  - gt  c1 addAll c2                        When compiled and run with JDK 14  at the time of writing  this an early access build  using the --enable-preview flag  you get the following result    CountForIndex index 0  count 0   CountForIndex index 2  count 0   CountForIndex index 4  count 0

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It appears that the full example can be solved without the use of any kind of Pair structure  The key is to filter on the column indexes  with the predicate checking the entire column  instead of mapping the column indexes to the number of false entries in that column   The code that does this is here       System out println          IntStream range 0  acyclic graph length               filter i - gt  IntStream range 0  acyclic graph length                                     noneMatch j - gt  acyclic graph j  i                 boxed                collect toList        This results in output of  0  2  4  which is I think the correct result requested by the OP   Also note the boxed   operation that boxes the int values into Integer objects  This enables one to use the pre-existing toList   collector instead having to write out collector functions that do the boxing themselves

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Since you only care about the indexes  you don t need to map to tuples at all   Why not just write a filter that uses the looks up elements in your array        int   value          IntStream range 0  value length               filter i - gt  value i   gt  30     or whatever filter you want              forEach i - gt  System out println i

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Eclipse Collections has Pair and all combinations of primitive object Pairs  for all eight primitives      The Tuples factory can create instances of Pair  and the PrimitiveTuples factory can be used to create all combinations of primitive object pairs   We added these before Java 8 was released   They were useful to implement key value Iterators for our primitive maps  which we also support in all primitive object combinations   If you re willing to add the extra library overhead  you can use Stuart s accepted solution and collect the results into a primitive IntList to avoid boxing   We added new methods in Eclipse Collections 9 0 to allow for Int Long Double collections to be created from Int Long Double Streams   IntList list   IntLists mutable withAll intStream     Note  I am a committer for Eclipse Collections

[java] Does Java SE 8 have Pairs or Tuples?

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