Storing number pairs in java

Question

How do I store a set of paired numbers in java? Do I use lists or arrays or maybe something else?

eg. [ (1,1) , (2,1) , (3,5)]

Answer 1

You can use the class Pair!

    import javafx.util.Pair;

    int x = 23;
    int y = 98;

    Pair<Integer, Integer> pair1 = new Pair<>(6, 7);
    Pair <Integer, Integer> pair2 = new Pair<>(x, y);

I hope this helps you!

Answer 2

There are a few options:

Write a custom IntPair class

class IntPair {
  // Ideally, name the class after whatever you're actually using 
  // the int pairs *for.*
  final int x;
  final int y;
  IntPair(int x, int y) {this.x=x;this.y=y;}
  // depending on your use case, equals? hashCode?  More methods?
}

and then create an IntPair[] or a List<IntPair>.

Alternately, create a two-dimensional array new int[n][2], and treat the rows as pairs.

Java doesn't have a built-in Pair class for a few reasons, but the most noticeable is that it's easy enough to write a class that has the same function, but has much more enlightening, helpful names for the class, its fields, and its methods.

If we knew more about what you're actually using this for, we might be able to provide more detailed suggestions -- for all we know, a Map could be appropriate here.

Answer 3

If you're needing to avoid duplicates then a HashSet would be a good choice but it not then an ArrayList would work.

Class IntPair(){
  int i;
  int j;
}
HashSet<IntPair> set = new HashSet<IntPair>();

or

ArrayList<IntPair> list = new ArrayList<IntPair>();

Answer 4

class Pair<T> {
    T p1, p2;
    Pair(T p1, T p2) {
        this.p1 = p1;
        this.p2 = p2;
    }

Pair<Integer> pair = new Pair<Integer>(1,2);

int i1 = pair.p1;
int i2 = pair.p2;

You can also put in getters, setters, equals, hashcode, etc.

Answer 5

If you can live with low level structures and desperately need compact form of "literal" form of "set of pairs" -- this happens to me in unit test, when I need a set of fixtures -- you can simply use an array of arrays:

int[][] squares = {
    { 1, 1 },
    { 2, 4 },
    { 3, 9 }
};

But keep in mind that there is no semantic to such a type -- it all depends on proper use, compiler won't give you a warning if you type squares[0][1] when you really wanted squares[1][0].