Pair Class – Java Implementation

Class Pair<Key, Value> – A convenience class to represent name-value pairs. pair stores a key-pair value. Two Pair objects are considered equal if key and value of one pair is matching with second key. This class also generates hash code using key and value. So hash code will also be same for two Pair objects if their keys and values are same.

Constructor Detail:

public Pair(K key,   V value)

Creates a new pair

Parameters:

key – The key for this pair
value – The value to use for this pair

Methods and description:

Return Type	Method	Description
key for this pair	getKey()	Gets the key for this pair.
value for this pair	getValue()	Gets the value for this pair.
int (hash code for this Pair)	hashCode()	Generate a hash code for this Pair. The hash code is calculated using both the name and the value of the Pair.
String	toString()	String representation of this Pair.
boolean	equals(Object o)	If the Object to be tested is not a Pair or is null, then this method returns false. Two Pairs are considered equal if and only if both the names and values are equal. Example: Pair<String,Integer> p1 = new Pair(1,5); Pair p2 = new Pair(1,5); Pair p3 = new Pair(2,6); System.out.println(p1.equals(p2) + " " + p2.equals(p3)); Output: true false

Example:

	import javafx.util.Pair;
	import java.util.ArrayList;

	public class PairExample {
	public static void main(String[] args) {
	Pair<String, Integer> pair1 = new Pair<>("apple",1);
	Pair<String, Integer> pair2 = new Pair<>("apple",1);
	Pair<String, Integer> pair3 = new Pair<>("banana",2);
	Pair<String, Integer> pair4 = new Pair<>("pineapple",4);

	ArrayList<Pair<String,Integer>> list = new ArrayList<>();
	list.add(pair1);
	list.add(pair2);
	list.add(pair3);
	list.add(pair4);

	//toString function
	System.out.println("——–toString function——–");
	for(Pair p: list){
	System.out.println(p.toString());
	}

	//equals function
	System.out.println("——–equals function——–");
	System.out.println("pair1 and pair2 are equal: " + pair1.equals(pair2));
	System.out.println("pair1 and pair3 are equal: " + pair1.equals(pair3));
	System.out.println("pair3 and pair4 are equal: " + pair3.equals(pair4));

	//getKey and getValue function
	System.out.println("——–getKey and getValue function——–");
	for (Pair p: list){
	System.out.println("key: " + p.getKey() + " and its value: " + p.getValue());
	}

	//hashCode function
	System.out.println("——–hashCode function——–");
	for (Pair p: list){
	System.out.println("Pair: " + p.toString() + " and hashCode: " + p.hashCode());
	}
	System.out.println(" As you can see that hashcode for pair1 and pair2" +
	" are same since key and values are equal");
	}
	}

view raw

PairExample.java

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Output:

--------toString function--------
apple=1
apple=1
banana=2
pineapple=4
--------equals function--------
pair1 and pair2 are equal: true
pair1 and pair3 are equal: false
pair3 and pair4 are equal: false
--------getKey and getValue function--------
key: apple and its value: 1
key: apple and its value: 1
key: banana and its value: 2
key: pineapple and its value: 4
--------hashCode function--------
Pair: apple=1 and hashCode: 1209379731
Pair: apple=1 and hashCode: 1209379731
Pair: banana=2 and hashCode: -972748765
Pair: pineapple=4 and hashCode: -1349826842
As you can see that hashcode for pair1 and pair2 are same since key and values are equal

Reference: wiki

Java Pair Class

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