A Java collection of value pairs tuples

Question

I like how Java has a Map where you can define the types of each entry in the map  for example  lt String  Integer gt     What I m looking for is a type of collection where each element in the collection is a pair of values   Each value in the pair can have its own type  like the String and Integer example above   which is defined at declaration time     The collection will maintain its given order and will not treat one of the values as a unique key  as in a map      Essentially I want to be able to define an ARRAY of type  lt String Integer gt  or any other 2 types     I realize that I can make a class with nothing but the 2 variables in it  but that seems overly verbose     I also realize that I could use a 2D array  but because of the different types I need to use  I d have to make them arrays of OBJECT  and then I d have to cast all the time     I only need to store pairs in the collection  so I only need two values per entry   Does something like this exist without going the class route   Thanks

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Map Entry  These built-in classes are an option  too  Both implement the Map Entry interface    AbstractMap SimpleEntry AbstractMap SimpleImmutableEntry

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Spring has a Pair lt S T gt  type in the Data Utils package org springframework data util  Pair lt String Integer gt  pair   Pair of  Test   123   System out println pair getFirst     System out println pair getSecond

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What about  Apache Commons Lang 3  Pair class and the relative subclasses        import org apache commons lang3 tuple ImmutablePair      import org apache commons lang3 tuple Pair               SuppressWarnings  unchecked       Pair lt String  Integer gt    arr   new ImmutablePair                ImmutablePair of  A   1               ImmutablePair of  B   2            both access the  left  part     String key   arr 0  getKey        String left   arr 0  getLeft            both access the  right  part     Integer value   arr 0  getValue        Integer right   arr 0  getRight      ImmutablePair is a specific subclass that does not allow the values in the pair to be modified  but there are others implementations with different semantic  These are the Maven coordinates  if you need them            lt dependency gt               lt groupId gt org apache commons lt  groupId gt               lt artifactId gt commons-lang3 lt  artifactId gt               lt version gt 3 4 lt  version gt           lt  dependency gt

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This is based on JavaHelp4u  s code    Less verbose and shows how to do in one line and how to loop over things            gt   Imports import java util AbstractMap SimpleEntry  import java util ArrayList  import java util List  import java util Map Entry            gt   Single Entry SimpleEntry lt String  String gt  myEntry   new SimpleEntry lt String  String gt   ID    Text    System out println  key      myEntry getKey          value     myEntry getValue     System out println              gt   List of Entries List lt Entry lt String String gt  gt  pairList   new ArrayList lt  gt        -- Specify manually Entry lt String String gt  firstButton   new SimpleEntry lt String  String gt   Red     Way out    pairList add firstButton      -- one liner  pairList add new SimpleEntry lt String String gt   Gray    Alternate route        Ananomous add     -- Iterate over Entry array  for  Entry lt String  String gt  entr   pairList        System out println  Button      entr getKey          Label      entr getValue

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Java 9   In Java 9  you can simply write  Map entry key  value   to create an immutable pair    Note  this method does not allow keys or values to be null  If you want to allow null values  for example  you d want to change this to  Map entry key  Optional ofNullable value       Java 8   In Java 8  you can use the more general-purpose javafx util Pair to create an immutable  serializable pair  This class does allow null keys and null values   In Java 9  this class is included in the javafx base module   EDIT  As of Java 11  JavaFX has been decoupled from the JDK  so you d need the additional maven artifact org openjfx javafx-base     Java 6   In Java 6 and up  you can use the more verbose AbstractMap SimpleImmutableEntry for an immutable pair  or AbstractMap SimpleEntry for a pair whose value can be changed  These classes also allow null keys and null values  and are serializable     Android  If you re writing for Android  just use Pair create key  value  to create an immutable pair     Apache Commons  Apache Commons Lang provides the helpful Pair of key  value  to create an immutable  comparable  serializable pair     Eclipse Collections  If you re using pairs that contain primitives  Eclipse Collections provides some very efficient primitive pair classes that will avoid all the inefficient auto-boxing and auto-unboxing    For instance  you could use PrimitiveTuples pair int  int  to create an IntIntPair  or PrimitiveTuples pair float  long  to create a FloatLongPair      Project Lombok  Using Project Lombok  you can create an immutable pair class simply by writing    Value public class Pair lt K  V gt        K key      V value      Lombok will fill in the constructor  getters  equals    hashCode    and toString   methods for you automatically in the generated bytecode  If you want a static factory method instead of a constructor  e g   a Pair of k  v   simply change the annotation to   Value staticConstructor    of       Otherwise  If none of the above solutions float your boat  you can simply copy and paste the following code  which  unlike the class listed in the accepted answer  guards against NullPointerExceptions    import java util Objects   public class Pair lt K  V gt         public final K key      public final V value       public Pair K key  V value            this key   key          this value   value             public boolean equals Object o            return o instanceof Pair  amp  amp  Objects equals key    Pair lt     gt  o  key   amp  amp  Objects equals value    Pair lt     gt  o  value              public int hashCode             return 31   Objects hashCode key    Objects hashCode value              public String toString             return key         value

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In project Reactor  io projectreactor reactor-core  there is advanced support for n-Tuples   Tuple2 lt String  Integer gt  t   Tuples of  string   1    There you can get t getT1    t getT2        Especially with Stream or Flux you can even map the tuple elements   Stream lt Tuple2 lt String  Integer gt  gt  s  s map t - gt  t mapT2 i - gt  i   2

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AbstractMap SimpleEntry  Easy you are looking for this   java util List lt java util Map Entry lt String Integer gt  gt  pairList  new java util ArrayList lt  gt       How can you fill it   java util Map Entry lt String Integer gt  pair1 new java util AbstractMap SimpleEntry lt  gt   Not Unique key1  1   java util Map Entry lt String Integer gt  pair2 new java util AbstractMap SimpleEntry lt  gt   Not Unique key2  2   pairList add pair1   pairList add pair2     This simplifies to   Entry lt String Integer gt  pair1 new SimpleEntry lt  gt   Not Unique key1  1   Entry lt String Integer gt  pair2 new SimpleEntry lt  gt   Not Unique key2  2   pairList add pair1   pairList add pair2     And  with the help of a createEntry method  can further reduce the verbosity to   pairList add createEntry  Not Unique key1   1    pairList add createEntry  Not Unique key2   2      Since ArrayList isn t final  it can be subclassed to expose an of method  and the aforementioned createEntry method   resulting in the syntactically terse   TupleList lt java util Map Entry lt String Integer gt  gt  pair   new TupleList lt  gt     pair of  Not Unique key1   1   pair of  Not Unique key2   2

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The preferred solution as you ve described it is a List of Pairs  i e  List    To accomplish this you would create a Pair class for use in your collection  This is a useful utility class to add to your code base    The closest class in the Sun JDK providing functionality similar to a typical Pair class is AbstractMap SimpleEntry  You could use this class rather than creating your own Pair class  though you would have to live with some awkward restrictions and I think most people would frown on this as not really the intended role of SimpleEntry  For example SimpleEntry has no  setKey    method and no default constructor  so you may find it too limiting   Bear in mind that Collections are designed to contain elements of a single type  Related utility interfaces such as Map are not actually Collections  i e  Map does not implement the Collection interface   A Pair would not implement the Collection interface either but is obviously a useful class in building larger data structures

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The Pair class is one of those  gimme  generics examples that is easy enough to write on your own  For example  off the top of my head   public class Pair lt L R gt       private final L left    private final R right     public Pair L left  R right        assert left    null      assert right    null       this left   left      this right   right         public L getLeft     return left      public R getRight     return right        Override   public int hashCode     return left hashCode     right hashCode          Override   public boolean equals Object o        if    o instanceof Pair   return false      Pair pairo    Pair  o      return this left equals pairo getLeft     amp  amp             this right equals pairo getRight              And yes  this exists in multiple places on the Net  with varying degrees of completeness and feature    My example above is intended to be immutable

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Apache Crunch also has a Pair class  http   crunch apache org apidocs 0 5 0 org apache crunch Pair html

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Apache common lang3 has Pair class and few other libraries mentioned in this thread What is the equivalent of the C   Pair lt L R gt  in Java   Example matching the requirement from your original question   List lt Pair lt String  Integer gt  gt  myPairs   new ArrayList lt Pair lt String  Integer gt  gt     myPairs add Pair of  val1   11    myPairs add Pair of  val2   17            for Pair lt String  Integer gt  pair   myPairs        following two lines are equivalent    whichever is easier for you      System out println pair getLeft            pair getRight       System out println pair getKey            pair getValue

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You could write a generic Pair lt A  B gt  class and use this in an array or list   Yes  you have to write a class  but you can reuse the same class for all types  so you only have to do it once

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just create a class like  class tuples     int x  int y       then create List of this objects of tuples  List lt tuples gt  list   new ArrayList lt tuples gt       so you can also implement other new data structures in the same way

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What about com sun tools javac util Pair

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Expanding on the other answers a generic immutable Pair should have a static method to avoid cluttering your code with the call to the constructor     class Pair lt L R gt          final L left        final R right         public Pair L left  R right            this left   left          this right   right                 static  lt L R gt  Pair lt L R gt  of L left  R right             return new Pair lt L R gt  left  right               if you name the static method  of  or  pairOf  the code becomes fluent as you can write either        list add Pair of x y       my preference     list add pairOf x y       use with import static x y Pair pairOf   its a real shame that the core java libraries are so sparse on such things that you have to use commons-lang or other 3rd parties to do such basic stuff  yet another reason to upgrade to scala

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I mean  even though there is no Pair class in Java there is something pretty simmilar  Map Entry  Map Entry Documentation  This is  simplifying quite a bit  what HashMap   or actually any Map stores   You can create an instance of Map store your values in it and get the entry set  You will end up with a Set lt Map Entry lt K V gt  gt  which effectively is what you want   So   public static void main String   args            HashMap lt String  Integer gt  values   new HashMap lt String Integer gt         values put  A   235    your custom data  the types may be different       more data insertions         Set lt Map Entry lt String Integer gt  gt  list   values entrySet     your list        do as you may with it

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I was going to ask if you would not want to just use a List lt Pair lt T  U gt  gt   but then  of course  the JDK doesn t have a Pair lt   class   But a quick Google found one on both Wikipedia  and forums sun com   Cheers

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To anyone developing for Android  you can use android util Pair

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First Thing on my mind when talking about key value pairs is the Properties Class where you can save and load items to a stream file

[java] A Java collection of value pairs? (tuples?)

`Map.Entry`

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