Java Programming HashSet Collection

What is HashSet Collection in java?

  • HashSet class is one of the collection class in java.
  • HashSet class extends AbstractSet and implements the Set interface.
  • HashSet class is used to create a collection that uses a hash table for storage. hash table stores the information using a mechanishm called hashing.
  • In hashing, hash code (the informational content of a key) is used to determine a unique value.

HashSet Constructors Types

HashSet()

This constructor builds an empty HashSet.

HashSet(Collection collection)

This constructor initializes the elements of the collection.

HashSet(int capacity)

Initializes the capacity of the hash set to capacity.

HashSet(int capacity, float loadCapacity)

Initializes the capacity and fill ratio(also called load capacity) of the hash set.

HashSet Methods

add method

add method is used to add element in the HashSet.

add(object)

contains method

contains method is used to check whether element exists in HashSet or not. returns true if object exist in HashSet, otherwise returns false.

contains(object)

remove method

remove method is used to remove element in the HashSet.

remove(object)

size method

size method is used to return the number of elements in the HashSet.

size()

Creating HashSet and Adding Elements in Java Program

// Codingpointer Demonstrates HashSet
                                                                                
import java.util.*;                                                             
                                                                                
class HashSetTest {                                                          
 public static void main(String args[]) {                                       
  HashSet hs = new HashSet();
  //Add elements
  hs.add("B");
  hs.add("E");
  hs.add("D");
  hs.add("E");
  System.out.println(hs);           
 }                                                                              
}  
Output:
$ java HashSetTest     
[B, D, E]   

Remove Element in HashSet

import java.util.*;                                                             
                                                                                
class HashSetTest {                                                          
 public static void main(String args[]) {                                       
  HashSet hs = new HashSet();
  //Add elements
  hs.add("B");
  hs.add("E");
  hs.add("D");
  hs.add("E");
  System.out.println(hs);  
  System.out.println("HashSet contains 'B':" + hs.contains("B"));         
  System.out.println("HashSet contains 'R':" + hs.contains("R"));
  System.out.println("Size: "+hs.size());
  hs.remove("E");
  System.out.println("after removed 'E'");
  System.out.println(hs);
  System.out.println("Size: "+hs.size());
 }                                                                              
}
Output:
java HashSetTest          
[B, D, E]                              
HashSet contains 'B':true                            
HashSet contains 'R':false                                      
Size: 3                               
after removed 'E'                             
[B, D]                          
Size: 2  

Adding Element of Different Data Types

import java.util.*;                                                             
                                                                                
class HashSetTest {                                                          
 public static void main(String args[]) {                                       
  HashSet hs = new HashSet();
  //Add elements
  hs.add("B");
  hs.add("E");
  hs.add(2);
  hs.add("E");
  System.out.println(hs);  
  System.out.println("HashSet contains 'B':" + hs.contains("B"));         
  System.out.println("HashSet contains 'R':" + hs.contains("R"));
  System.out.println("Size: "+hs.size());
  hs.remove("E");
  System.out.println("after removed 'E'");
  System.out.println(hs);
  System.out.println("Size: "+hs.size());
 }                                                                              
}
Output:
java HashSetTest          
[B, 2, E]                              
HashSet contains 'B':true                            
HashSet contains 'R':false                                      
Size: 3                               
after removed 'E'                             
[B, 2]                          
Size: 2  

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