Circular collection with 2 values

Is there some collection in Java in which I can put 2 objects and then by calling a method on one to return the other one?
Example: myColection [o1,o2] myCollection.getNext(o1) to retunr o2 and viceversa.

if(param == o1) return o2; else if(param == o2) return o1; else throw Exception;

next()

4 Answers
4

There is no collection available in Java which can solve this problem directly. I guess writing own custom logic would be the solution.

I tried something like below:

import java.util.*;
import java.lang.*;
import java.io.*;

class Node
String data;
Node otherNode;
Node(String data)
this.data=data;

Node getOtherNode()
return otherNode;

@Override
public String toString()
return this.data;




class Ideone


public static void main (String args) throws java.lang.Exception


Node first = new Node("FIRST");
Node second = new Node("SECOND");
first.otherNode = second;
second.otherNode = first;

System.out.println(first.getOtherNode());




Link to code:https://www.ideone.com/MA7v6L

How about using a Map?

public static <T> Map<T, T> alternate(T s1, T s2)

Map<T, T> map = new HashMap<>();
map.put(s1, s2);
map.put(s2, s1);
return map;


public static void main(String args)

Map<String, String> map = alternate("hello", "world");

System.out.println(map.get("hello"));
System.out.println(map.get("world"));



If you want a circular collection of any number of elements, the easiest would be to extend ArrayDeque with the methods you want.

ArrayDeque

This allows you to still use all the normal Deque methods for adding and removing elements to/from the collection.

Deque

public class CircularArrayDeque<E> extends ArrayDeque<E>
public CircularArrayDeque()
super();

public CircularArrayDeque(Collection<? extends E> c)
super(c);

public CircularArrayDeque(int numElements)
super(numElements);

/**
* Retrieves the first element of this deque and moves it to the end, or
* returns @code null if this deque is empty.
*
* @return the head of this deque, or @code null if this deque is empty
*/
public E getNext()
E elem = pollFirst();
if (elem != null)
addLast(elem);
return elem;

/**
* Retrieves the last element of this deque and moves it to the front, or
* returns @code null if this deque is empty.
*
* @return the tail of this deque, or @code null if this deque is empty
*/
public E getPrevious()
E elem = pollLast();
if (elem != null)
addFirst(elem);
return elem;




In case you are looking by for something like a Pair in C++, you need to implement it on your own.

class Pair<K, V>
private K object1;
private V object2;

Pair(K key, V value)
this.object1 = key;
this.object2 = value;


public K getObject1() return this.object1;
public V getObject2() return this.object2;


// object initialization
Pair<String, Integer> p = new Pair("age", 24);


Using the above class, you can obtain the necessary functionality.
If you are looking for a circular list, you can use ArrayList and modify the get method.

class CircularList<T>
private List<T> list;
public CircularList()
list = new ArrayList();

public getNext(int index)
return list.get((index+1) % list.size());




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