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 .

What I\'m looking for is a type

Answer 1

To anyone developing for Android, you can use android.util.Pair. :)

Answer 2

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<L,R> {
      final L left;
      final R right;

      public Pair(L left, R right) {
        this.left = left;
        this.right = right;
      }

      static <L,R> Pair<L,R> of(L left, R right){
          return new Pair<L,R>(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...

Answer 3

Apache Crunch also has a Pair class: http://crunch.apache.org/apidocs/0.5.0/org/apache/crunch/Pair.html

Answer 4

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<Map.Entry<K,V>> which effectively is what you want.

So:

public static void main(String []args)
{    
    HashMap<String, Integer> values = new HashMap<String,Integer>();
    values.put("A", 235);//your custom data, the types may be different
    //more data insertions....
    Set<Map.Entry<String,Integer>> list = values.entrySet();//your list 
    //do as you may with it
}

Answer 5

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

Answer 6

What about com.sun.tools.javac.util.Pair?