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)]

You can use all the above, but there is no way of guessing from what you have said. — Peter Lawrey, Apr 19 '12 at 18:31
@Erwald Its one solution but it might not be the best for what the OP is doing. — Peter Lawrey, Apr 19 '12 at 18:32
[Related](http://stackoverflow.com/questions/9568403/how-to-store-an-array-of-pairs-in-java) — Rob Hruska, Apr 19 '12 at 18:37
[Related](http://stackoverflow.com/questions/521171/a-java-collection-of-value-pairs-tuples) — Rob Hruska, Apr 19 '12 at 18:37
Well the best solution will depend on how the numbers are being accessed. Are duplicates pairs allowed? If not, is the first value in a pair always unique? Will you be adding and removing, essentially? Do you want to have them sorted in some way? Are negative integers allowed? Using a Pair class as some have suggested is an option but I need the answers to those questions to give a better response. — Jesus is Lord, Apr 19 '12 at 18:38
[Related](http://stackoverflow.com/questions/2670982/using-tuples-in-java) — Rob Hruska, Apr 19 '12 at 18:39

Louis Wasserman · Accepted Answer · 2012-04-19T18:40:56.307

15

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.

edited Apr 19 '12 at 18:40

answered Apr 19 '12 at 18:35

Louis Wasserman

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I have an 2D array of characters. And I want to store certain postions separately. Helps? – saviok Apr 19 '12 at 18:58
Are you storing positions in the 2D array? (In that case, the options I outlined above are probably the best ones available.) – Louis Wasserman Apr 19 '12 at 19:01
Actually the question was for how to store the positions? – saviok Apr 19 '12 at 19:04
Then these options are probably the best ones available, although I might name the class `ArrayPosition` or something. – Louis Wasserman Apr 19 '12 at 19:05
I'm sorry could you help me a bit more? How do I actually declare that List? – saviok Apr 19 '12 at 20:10
Um. `List list = new ArrayList()`. You should read a Java tutorial, if you don't know that. – Louis Wasserman Apr 19 '12 at 20:15

fuggerjaki61 · Answer 2 · 2021-02-01T16:40:29.793

1

If you're using JavaFX, 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);

edited Feb 01 '21 at 16:40

answered Jan 21 '19 at 17:19

fuggerjaki61

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That's only for javafx applications. You're not like using that for an Android app for example... – Fran Marzoa Jul 02 '19 at 16:23

score 1 · Answer 3 · answered Aug 01 '21 at 16:37

Way 1 : Using javafx.util.Pair class

Pair<Integer> myPair1 = new Pair<Integer>(10,20);
Pair<Integer> myPair2 = new Pair<Integer>(30,40);
HashSet<Pair<Integer>> set = new HashSet<>(); // Java 8 and above
set.add(myPair1);
set.add(myPair2);

Way 2: Using int[] of size 2

int[] myPair1 = new int[] {10,20}; // myPair1[0]=10 , myPair[1] = 20
int[] myPair2 = new int[] {30,40};
HashSet<int[]> set = new HashSet<>(); // Java 8 and above

Way 3 : Converting pair into single number

int myPair1 = 10 * 1000 + 20; 
// int first = myPair1 / 1000; second = myPair2 % 1000;
int myPair2 = 30 * 1000 + 40;
HashSet<Integer> set = new HashSet<>();
set.add(myPair1);
set.add(myPair2);

Way 4 : Using ArrayList instead of int[] in way 2

Way 5 : Custom class that uses HashSet and Pair internally

score 0 · Answer 4 · answered Apr 19 '12 at 18:34

0

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.

answered Apr 19 '12 at 18:34

Skip Head

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I would made `p1`,`p2` `private final` and also override `equals()` and `hashCode()` – amit Apr 19 '12 at 18:34

score 0 · Answer 5 · answered Apr 19 '12 at 18:38

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].

score 0 · Answer 6 · answered Apr 19 '12 at 18:50

0

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>();

answered Apr 19 '12 at 18:50

ChadNC

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If you want to avoid duplicates you will need to also override equals and hashCode. http://stackoverflow.com/a/7520464/3215004 – gmatht Sep 16 '15 at 06:37

Storing number pairs in java

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