Importance of HashSet in Java

The HashSet use Hashing to manipulate data. Let us see an example −

Example

 import java.util.*; public class Demo{ private final String f_str, l_str; public Demo(String f_str, String l_str){ this.f_str = f_str; this.l_str = l_str; } public boolean equals(Object o){ if (o instanceof Demo) return true; Demo n = (Demo)o; return n.f_str.equals(f_str) && n.l_str.equals(l_str); } public static void main(String[] args){ Set<Demo> my_set = new HashSet<Demo>(); my_set.add(new Demo("Joe", "Goldberg")); System.out.println("Added a new element to the set"); System.out.println("Does the set contain a new instance of the object? "); System.out.println(my_set.contains(new Demo("Jo", "Gold"))); } } 

Output

 Added a new element to the set Does the set contain a new instance of the object? false 

The ?Demo' class contains a final string and a constructor. An equals function is defined that checks if an object is an instance of a specific class. It returns true if it is an instance otherwise casts the object to the class and checks using the 'equals' function. In the main function, a new Set is created and an instance is created. This is checked for using the ?instanceof' operator.