Didn t Java once have a Pair class

Question

Am I remembering incorrectly  or did Java  once upon a time  provide a Pair class as part of its API

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It does seem odd  I found this thread  also thinking I d seen one in the past  but couldn t find it in Javadoc   I can see the Java developers  point about using specialised classes  and that the presence of a generic Pair class could cause developers to be lazy  perish the thought    However  in my experience  there are undoubtedly times when the thing you re modelling really is just a pair of things and coming up with a meaningful name for the relationship between the two halves of the pair  is actually more painful than just getting on with it  So instead  we re left to create a  bespoke  class of practically boiler-plate code - probably called  Pair    This could be a slippery slope  but a Pair and a Triplet class would cover a very large proportion of the use-cases

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There are lots of implementation around here  but all the time something is missing   the Override of equal and hash method   here is a more complete version of this class          Container to ease passing around a tuple of two objects  This object provides a sensible    implementation of equals    returning true if equals   is true on each of the contained    objects      public class Pair lt F  S gt        public final F first      public final S second                  Constructor for a Pair                 param first the first object in the Pair         param second the second object in the pair             public Pair F first  S second            this first   first          this second   second                        Checks the two objects for equality by delegating to their respective          link Object equals Object   methods                 param o the   link Pair  to which this one is to be checked for equality         return true if the underlying objects of the Pair are both considered                equal              Override     public boolean equals Object o            if    o instanceof Pair                 return false                    Pair lt      gt  p    Pair lt      gt   o          return Objects equals p first  first   amp  amp  Objects equals p second  second                         Compute a hash code using the hash codes of the underlying objects                return a hashcode of the Pair              Override     public int hashCode             return  first    null   0   first hashCode       second    null   0   second hashCode                           Convenience method for creating an appropriately typed pair          param a the first object in the Pair         param b the second object in the pair         return a Pair that is templatized with the types of a and b             public static  lt A  B gt  Pair  lt A  B gt  create A a  B b            return new Pair lt A  B gt  a  b

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If you want a pair  not supposedly key-value pair  just to hold two generic data together neither of the solutions above really handy since first  or so called Key  cannot be changed  neither in Apache Commons Lang s Pair nor in AbstractMap SimpleEntry   They have thier own reasons  but still you may need to be able to change both of the components  Here is a Pair class in which both elements can be set  public class Pair lt First  Second gt        private First first      private Second second       public Pair First first  Second second            this first   first          this second   second             public void setFirst First first            this first   first             public void setSecond Second second            this second   second             public First getFirst             return first             public Second getSecond             return second             public void set First first  Second second            setFirst first           setSecond second               Override     public boolean equals Object o            if  this    o  return true          if  o    null    getClass      o getClass    return false           Pair pair    Pair  o           if  first    null    first equals pair first    pair first    null  return false          if  second    null    second equals pair second    pair second    null  return false           return true              Override     public int hashCode             int result   first    null   first hashCode     0          result   31   result    second    null   second hashCode     0           return result

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Many 3rd party libraries have their versions of Pair  but Java has never had such a class  The closest is the inner interface java util Map Entry  which exposes an immutable key property and a possibly mutable value property

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This should help   To sum it up  a generic Pair class doesn t have any special semantics and you could as well need a Tripplet class etc  The developers of Java thus didn t include a generic Pair but suggest to write special classes  which isn t that hard  like Point x y   Range start  end  or Map Entry key  value

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No  but it s been requested many times

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Map Entry  Java 1 6 and upper have two implementation of Map Entry interface pairing a key with a value     AbstractMap SimpleEntry  AbstractMap SimpleImmutableEntry     For example  Map Entry  lt  Month  Boolean  gt  pair        new AbstractMap SimpleImmutableEntry  lt  gt            Month AUGUST            Boolean TRUE               pair toString    AUGUST true   I use it when need to store pairs  like size and object collection    This piece from my production code   public Map lt L1Risk  Map Entry lt int    Map lt L2Risk  Map Entry lt int    Map lt L3Risk  List lt Event gt  gt  gt  gt  gt  gt          getEventTable RiskClassifier classifier        Map lt L1Risk  Map Entry lt int    Map lt L2Risk  Map Entry lt int    Map lt L3Risk  List lt Event gt  gt  gt  gt  gt  gt  l1s   new HashMap lt  gt         Map lt L2Risk  Map Entry lt int    Map lt L3Risk  List lt Event gt  gt  gt  gt  l2s   new HashMap lt  gt         Map lt L3Risk  List lt Event gt  gt  l3s   new HashMap lt  gt         List lt Event gt  events   new ArrayList lt  gt                 map put l3s  events       map put l2s  new AbstractMap SimpleImmutableEntry lt  gt  l3Size  l3s        map put l1s  new AbstractMap SimpleImmutableEntry lt  gt  l2Size  l2s        Code looks complicated but instead of Map Entry you limited to array of object  with size 2  and lose type checks

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No but JavaFX has it   Cf  Stack Overflow  Java Pair class implementation

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A Pair class    public class Pair lt K  V gt         private final K element0      private final V element1       public static  lt K  V gt  Pair lt K  V gt  createPair K element0  V element1            return new Pair lt K  V gt  element0  element1              public Pair K element0  V element1            this element0   element0          this element1   element1             public K getElement0             return element0             public V getElement1             return element1             usage    Pair lt Integer  String gt  pair   Pair createPair 1   test    pair getElement0    pair getElement1      Immutable  only a pair

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There is no Pair in the standard framework  but the Apache Commons Lang  which comes quite close to    standard     has a Pair

[java] Didn't Java once have a Pair class?

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