JAVA: USING HASHSET TO COUNT UNIQUE ELEMENTS.

COUNT UNIQUE ELEMENTS USING HASHSET IN JAVA

//sometimes you may come across requirement to count unique objects.

//In that case one of the solution is to create a hashset field/attribute in the class.

//For eg. animal is a class with name variable. zoo is a class which holds collections of animals.

//so if i want to count unique animals in zoo. i added hashset in the zoo class. 

//set is a collection which holds only unique elements. but lists holds duplicate values.

import java.util.ArrayList;

import java.util.HashSet;

class Animal{

String name;

public Animal(String name){

this.name = name;

}

}

class Zoo{

//list of animals present in zoo, multiple animals of same species also present in zoo

ArrayList<Animal> animalList = new ArrayList<Animal>();

//to track unique animals hashset is one of the solution

HashSet<String> uniqueAnimals = new HashSet<String>();

}

public class TestZoo{

public static void main(String[] args){

Animal elephant = new Animal("elephant");

Animal dog = new Animal("dog");

//dog repeated twice

Animal anotherDog = new Animal("dog");

Animal crocodile = new Animal("crocodile");

//crocodile repeated twice

Animal anotherCrocodile = new Animal("crocodile");

//add all animals to zoo

Zoo zoo = new Zoo();

ArrayList<Animal> addAnimalsTOzoo = new ArrayList<Animal>();

addAnimalsTOzoo.add(elephant);

addAnimalsTOzoo.add(dog);

addAnimalsTOzoo.add(anotherDog);

addAnimalsTOzoo.add(crocodile);

addAnimalsTOzoo.add(anotherCrocodile);

zoo.animalList = addAnimalsTOzoo; 

//use hashset to count unique animals

HashSet<String> countUniqueAnimals = new HashSet();

countUniqueAnimals.add(elephant.name);

countUniqueAnimals.add(dog.name);

countUniqueAnimals.add(anotherDog.name);

countUniqueAnimals.add(crocodile.name);

countUniqueAnimals.add(anotherCrocodile.name);

zoo.uniqueAnimals = countUniqueAnimals;

System.out.println("unique animals count = "+zoo.uniqueAnimals.size());

}

}