What is HashSet | Collection in Java | Methods of HashSet | Java Programming

 package collection;

import java.util.ArrayList;

import java.util.HashSet;

import java.util.Iterator;

import java.util.Set;

public class HashSetDemo {

public static void main(String[] args) {

/* How to declare the hashset

HashSet myset=new HashSet();

Set myset1=new HashSet();

*/

/*if we want to store only homogenous data, then use wrapper class

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

HashSet <String>myset1=new <String>HashSet();

*/

// Adding element in hasSet

HashSet myset=new HashSet();

myset.add(90);

myset.add(90);

myset.add(null);

myset.add(null);

System.out.println(myset); // Insertion order is not presevered, and duplicate elements are not allowed

//if we try to insert duplicate then only one single element will be stored, keep only one element

//result will be [null, 90]

//How to remove specific element: Provide the elements's value not order or index

myset.remove(null);

System.out.println(myset);

//inserting element : is not possible in hashSet, we can only add the element at the end of hashset

//access specific element: is not possible as index is not preserved. But one alternative is there

// convert Hashset into array list then access the hashset element

//Converting hashset into arrayList

ArrayList al=new ArrayList(myset);

System.out.println(al.get(0));

//Add another element in the hashSet

myset.add("Tech Bharat");

System.out.println(myset);

//read all element by looping

//Approach By normal for loop is not possible 

// For each loop

for(Object x:myset)

{

System.out.println(x);

}

//Read element using iterator

Iterator <Object>it=myset.iterator();

while(it.hasNext())

{

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

}

//Remove multiple values in Hashset is not possible in HashSet

//Clear all the element in HashSet

myset.clear();

// check whether HashSet is empty or not

System.out.println(myset.isEmpty());

//Size of hashset

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

}

}