21 Jul Java HashSet

The HashSet implements the Set interface. Every item is unique in a HashSet. It is a part of the java.util package i.e., you need to import the java.util.HashSet package.

Let us see some LinkedList operation/ methods with examples:

• Create a HashSet
• Size of a Hashset
• Loop through the HashSet
• Remove an item from a HashSet
• Check if an item exists in a HashSet

Let us first see how to create a HashSet in Java:

Create a HashSet

To create a HashSet, set the type in angular braces i.e., use the wrapper class. For example, for creating a HashSet with string elements, use <String>:

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

Let us now see an example and create a HashSet in Java with string elements:

import java.util.HashSet;

public class Main {

  public static void main(String[] args) {
   
   HashSet<String> sports = new HashSet<String>();
    
   // Adding string elements
   sports.add("Cricket");
   sports.add("Football");
   sports.add("Tennis");
   sports.add("Badminton");
   sports.add("Basketball");
   sports.add("Volleyball");
    
   // Display the HashSet
   System.out.println("HashSet\n"+sports);
  }
}

Output

HashSet
[Cricket, Tennis, Volleyball, Badminton, Basketball, Football]

Size of HashSet

To get the size of HashSet i.e., how many elements does it have, use the size() method. Let us see an example:

import java.util.HashSet;

public class Main {

  public static void main(String[] args) {
   
   HashSet<String> sports = new HashSet<String>();
    
   // Adding string elements
   sports.add("Cricket");
   sports.add("Football");
   sports.add("Tennis");
   sports.add("Badminton");
   sports.add("Basketball");
   sports.add("Volleyball");
    
   // Display the HashSet
   System.out.println("HashSet\n"+sports);
   
   // Size of the HashSet
   System.out.println("\nHashSet Size = "+sports.size());
  }
}

Output

HashSet
[Cricket, Tennis, Volleyball, Badminton, Basketball, Football]

HashSet Size = 6

Loop through the HashSet

Use the for-each loop to loop through the ArrayList in Java. Let us see an example:

import java.util.HashSet;

public class Main {

  public static void main(String[] args) {
   
   HashSet<String> sports = new HashSet<String>();
    
   // Adding string elements
   sports.add("Cricket");
   sports.add("Football");
   sports.add("Tennis");
   sports.add("Badminton");
   sports.add("Basketball");
   sports.add("Volleyball");
    
   // Display the HashSet
   System.out.println("HashSet\n"+sports);
   
   // Loop through the HashSet
   for (String s : sports) {
     System.out.println(s);
  }
 }
}

Output

HashSet
[Cricket, Tennis, Volleyball, Badminton, Basketball, Football]
Cricket
Tennis
Volleyball
Badminton
Basketball
Football

Remove an item from a HashSet

To remove an element from a HashSet, use the remove() method. Set the element you want to remove as a parameter of the remove () method. For example, to remove the element “Football”, set it as:

sports.remove("Football");

Let us now see an example of removing an element from a HashSet in Java:

import java.util.HashSet;

public class Main {

  public static void main(String[] args) {
   
   HashSet<String> sports = new HashSet<String>();
    
   // Adding string elements
   sports.add("Cricket");
   sports.add("Football");
   sports.add("Tennis");
   sports.add("Badminton");
   sports.add("Basketball");
   sports.add("Volleyball");
    
   // Display the HashSet
   System.out.println("HashSet\n"+sports);
   
   // Remove an element using the remove() method
   sports.remove("Football");

   // Display the updated HashSet
   System.out.println("Updated HashSet\n"+sports);
 }
}

Output

HashSet
[Cricket, Tennis, Volleyball, Badminton, Basketball, Football]
Updated HashSet
[Cricket, Tennis, Volleyball, Badminton, Basketball]

Check if an item exists in a HashSet

The contains() method is used in a HashSet to check if an item exists. Let us see an example:

import java.util.HashSet;

public class Main {

  public static void main(String[] args) {
   
   HashSet<String> sports = new HashSet<String>();
    
   // Adding string elements
   sports.add("Cricket");
   sports.add("Football");
   sports.add("Tennis");
   sports.add("Badminton");
   sports.add("Basketball");
   sports.add("Volleyball");
    
   // Display the HashSet
   System.out.println("HashSet\n"+sports);
   
   // HashSet after removing an element
   System.out.println("\nDoes the HashSet contain an element Tennis?\n"+sports.contains("Tennis"));
 }
}

Output

HashSet
[Cricket, Tennis, Volleyball, Badminton, Basketball, Football]

Does the HashSet contain an element Tennis?
True

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