Creating a list of pairs in java

Question

Which class would work best for a non-ordered list of pairs  I ll be taking a bunch of  float short  pairs and will need to be able to perform simple math  like multiplying the pair together to return a single float  etc   List only takes one argument  and HashMap won t allow duplicates  as far as I know   Any thoughts

User · Answer

If you want multiplicities  you can put it in map that maps pair to ammount  This way there will only be one pair of given values  but it can represent multiple occurances   Then if you have lot of repeatet values and want to perform some operation on all values  you can save lot of computations

User · Answer

You can use the Entry lt U V gt  class that HashMap uses but you ll be stuck with its semantics of getKey and getValue   List lt Entry lt Float Short gt  gt  pairList           My preference would be to create your own simple Pair class   public class Pair lt L R gt        private L l      private R r      public Pair L l  R r           this l   l          this r   r            public L getL    return l        public R getR    return r        public void setL L l   this l   l        public void setR R r   this r   r        Then of course make a List using this new class  e g    List lt Pair lt Float Short gt  gt  pairList   new ArrayList lt Pair lt Float Short gt  gt       You can also always make a Lists of Lists  but it becomes difficult to enforce sizing  that you have only pairs  and you would be required  as with arrays  to have consistent typing

User · Answer

Sounds like you need to create your own pair class  see discussion here    Then make a List of that pair class you created

User · Answer

Use a List of custom class instances   The custom class is some sort of Pair or Coordinate or whatever   Then just  List lt Coordinate gt    new YourFavoriteListImplHere lt Coordinate gt      This approach has the advantage that it makes satisfying this requirement  perform simple math  like multiplying the pair together to return a single float  etc   clean  because your custom class can have methods for whatever maths you need to do

User · Answer

Similar to what Mark E has proposed  but no need to recreate the wheel  if you don t mind relying on 3rd party libs   Apache Commons has tuples already defined   org apache commons lang3 tuple Pair lt L R gt    Apache Commons is so pervasive  I typically already have it in my projects  anyway  https   mvnrepository com artifact org apache commons commons-lang3

User · Answer

Similar to what Mark E has proposed  you have to come up with your own  Just to help you a bit  there is a neat article http   gleichmann wordpress com 2008 01 15 building-your-own-literals-in-java-tuples-and-maps  which gives you a really neat way of creating tuples and maps that might be something you might want to consider

User · Answer

just fixing some small mistakes in Mark Elliot s code   public class Pair lt L R gt        private L l      private R r      public Pair L l  R r           this l   l          this r   r            public L getL    return l        public R getR    return r        public void setL L l   this l   l        public void setR R r   this r   r

[java] Creating a list of pairs in java

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