HashSet In Java

Hashset basic example in java

Introduction:

A HashSet is a collection of items where every item is unique, and it is found in the java.util package:

Example

Create a HashSet object called cars that will store strings:

import java.util.HashSet; // Import the HashSet class

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

Add Items

The HashSet class has many useful methods. For example, to add items to it, use the add() method

Program 1:adding items in hashset and printing it.

CODE:

// Import the HashSet class

import java.util.HashSet;

public class Main {

public static void main(String[] args) {

HashSet<String> Cricket = new HashSet<String>();//deaclaration of hashmap

Cricket.add(“Sachin”);

Cricket.add(“Virat”);

Cricket.add(“AB”);

Cricket.add(“Smith”);

Cricket.add(“Raina”);

System.out.println(Cricket);

}

}

OUTPUT:

[AB, Smith, Raina, Sachin, Virat]

Check If an Item Exists

To check whether an item exists in a HashSet, use the contains() method:

Program 2:check item exists or not.

CODE:

// Import the HashSet class

// Import the HashSet class

import java.util.HashSet;

public class Main {

public static void main(String[] args) {

HashSet<String> Cricket = new HashSet<String>();//deaclaration of hashmap

Cricket.add(“Sachin”);

Cricket.add(“Virat”);

Cricket.add(“AB”);

Cricket.add(“Smith”);

Cricket.add(“Raina”);

System.out.println(Cricket.contains(“Mazda”));//checking using cntains method

}

}

OUTPUT:

True

Remove an Item

To remove an item, use the remove() method

Program 3:remove element

CODE:

// Import the HashSet class

import java.util.HashSet;

public class Main {

public static void main(String[] args) {

HashSet<String> Cricket= new HashSet<String>();//deaclaration of hashmap

Cricket.add(“Sachin”);

Cricket.add(“Virat”);

Cricket.add(“AB”);

Cricket.add(“Smith”);

Cricket.add(“Raina”);

Cricket.remove(“Sachin”);

System.out.println(Cricket);

}

}

OUTPUT:

[AB, Smith, Raina, Virat]

Clear Method:

To remove all items, use the clear() method:

Program 4:remove all items using clear method

CODE:

// Import the HashSet class

import java.util.HashSet;

public class Main {

public static void main(String[] args) {

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

cars.add(“Volvo”);

cars.add(“BMW”);

cars.add(“Ford”);

cars.add(“BMW”);

cars.add(“Mazda”);

cars.clear();

System.out.println(cars);

}

}

OUTPUT:

[]

HashSet Size

To find out how many items there are, use the size method:

Program 5: To find out how many items there are, use the size method:

CODE:

// Import the HashSet class

import java.util.HashSet;

public class Main {

public static void main(String[] args) {

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

Cricketers.add(“Sachin”);

Cricketers.add(“Virat”);

Cricketers.add(“MSD”);

Cricketers.add(“Riyan”);

Cricketers.add(“yuzi”);

System.out.println(Cricketers.size());

}

}

OUTPUT:

4

Loop Through a HashSet

Loop through the items of an HashSet with a for-each loop:

Program 6:Using for eachloop printing set

CODE:

// Import the HashSet class

import java.util.HashSet;

public class Main {

public static void main(String[] args) {

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

Cricketers.add(“Sachin”);

Cricketers.add(“Virat”);

Cricketers.add(“MSD”);

Cricketers.add(“Riyan”);

Cricketers.add(“yuzi”);

for (String i :Cricketers ) {

System.out.println(i);

}

}

}

OUTPUT:

Sachin

Virat

MSD

Riyan

Yuzi

Other datatypes we can use

Items in an HashSet are actually objects. In the examples above, we created items (objects) of type “String”. Remember that a String in Java is an object (not a primitive type). To use other types, such as int, you must specify an equivalent wrapper class: Integer. For other primitive types, use: Boolean for boolean, Character for char, Double for double, etc:

HashSet<Integer> numbers = new HashSet<Integer>();

HashSet<Character > numbers = new HashSet<Character>();

Use a HashSet that stores Integer objects

Program 7:Integer types hashset

CODE:

import java.util.HashSet;

public class Main {

public static void main(String[] args) {

// Create a HashSet object called numbers

HashSet<Integer> numbers = new HashSet<Integer>();

// Add values to the set

numbers.add(4);

numbers.add(7);

numbers.add(8);

// Show which numbers between 1 and 10 are in the set

for(int i = 1; i <= 10; i++) {

if(numbers.contains(i)) {

System.out.println(i + “ was found in the set.”);

} else {

System.out.println(i + “ was not found in the set.”);

}

}

}

}

OUTPUT:

1 was not found in the set.
2 was not found in the set.
3 was not found in the set.
4 was found in the set.
5 was not found in the set.
6 was not found in the set.
7 was found in the set.
8 was found in the set.
9 was not found in the set.
10 was not found in the set.

Program 8:check wheather two set is equal or not.

CODE:

// Java code to illustrate the equals() method

import java.util.*;

public class Abstract_Set_Demo {

public static void main(String[] args)

{

// Creating an empty AbstractSet

AbstractSet<String>

abstract_set1 = new HashSet<String>();

AbstractSet<String>

abstract_set2 = new HashSet<String>();

// Adding elements to set

abstract_set1.add(“Somnath”);

abstract_set1.add(“4”);

//abstract_set1.add(“Sachin”);

abstract_set1.add(“Welcomes”);

abstract_set1.add(“You”);

// Adding elements to set

abstract_set2.add(“Somnath”);

abstract_set2.add(“4”);

//abstract_set2.add(“Sachin”);

abstract_set2.add(“Welcomes”);

abstract_set2.add(“You”);

// Displaying the first HashSet

System.out.println(“First Set: “

+ abstract_set1);

// Displaying the second HashSet

System.out.println(“Second Set: “

+ abstract_set2);

// Displaying the equality

System.out.println(“Equality: “

+ abstract_set1

.equals(abstract_set2));

}

}

OUTPUT:

First Set: [4, Somnath, You, Welcomes]
Second Set: [4, Somnath, You, Welcomes]
Equality: true

Java HashSet from another Collection

Using while loop iterating all element .we can use iterator method as well.

Program 9:iterating through while loop

CODE:

import java.util.*;

class HashSet4{

public static void main(String args[]){

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

list.add(“Ravi”);

list.add(“Vijay”);

list.add(“Ajay”);

HashSet<String> set=new HashSet(list);

set.add(“Gaurav”);

Iterator<String> i=set.iterator();

while(i.hasNext())

{

System.out.println(i.next());

}

}

OUTPUT:

Vijay
Ravi
Gaurav
Ajay
PROGRAM 10:Hashset iterator example
CODE:

// Java code to illustrate iterator()

import java.util.*;

import java.util.HashSet;

public class HashSetDemo {

public static void main(String args[])

{

// Creating an empty HashSet

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

// Use add() method to add elements into the Set

set.add(“Welcome”);

set.add(“To”);

set.add(“America”);

set.add(“and “);

set.add(“Portugiz”);

// Displaying the HashSet

System.out.println(“HashSet: “ + set);

// Creating an iterator

Iterator value = set.iterator();

// Displaying the values after iterating through the set

System.out.println(“The iterator values are: “);

while (value.hasNext()) {//chacking upto the null

System.out.println(value.next());

}

}

}

OUTPUT:
HashSet: [and, America, Welcome, To,portugiz]
The iterator values are:
and
America
Portugiz
To

Java HashSet Example: Book

Let’s see a HashSet example where we are adding books to set and printing all the book

Program 10:Accesing element using object and printing it .

CODE:

import java.util.*;

class Book {

int id;

String name,author,publisher;

int quantity;

public Book(int id, String name, String author, String publisher, int quantity) {

this.id = id;

this.name = name;

this.author = author;

this.publisher = publisher;

this.quantity = quantity;

}

}

public class HashSetExample {

public static void main(String[] args) {

HashSet<Book> set=new HashSet<Book>();

//Creating Books

Book b1=new Book(101,”Let us C”,”Yashwant Kanetkar”,”BPB”,8);

Book b2=new Book(102,”Data Communications & Networking”,”Forouzan”,”Mc Graw Hill”,4);

Book b3=new Book(103,”Operating System”,”Galvin”,”Wiley”,6);

//Adding Books to HashSet

set.add(b1);

set.add(b2);

set.add(b3);

//Traversing HashSet

for(Book b:set){

System.out.println(b.id+” “+b.name+” “+b.author+” “+b.publisher+” “+b.quantity);

}

}

}

OUTPUT:

101 Let us C Yashwant Kanetkar BPB 8
102 Data Communications & Networking Forouzan Mc Graw Hill 4
103 Operating System Galvin Wiley 6

Note*: Book b created object and acessing all elements.

Using for loop

Note*:Hash stores unique values not to be repeated

Thank you.do read all method and practise more.any query please ask us.