In Java, HashSet is a built-in implementation of the Set interface that uses a hash table to store its elements. HashSet does not allow duplicate elements, and the order of the elements is not preserved. Here’s an explanation of HashSet in Java with examples:
Creating a HashSet
To create a HashSet object in Java, you can use the HashSet class constructor. Here’s an example:
HashSet<String> set = new HashSet<String>();In this example, we have created a new HashSet object that can hold String values.
Adding and Removing Elements
You can add elements to a HashSet object using the add method. Here’s an example:
set.add("John");
set.add("Mary");In this example, we have added the names “John” and “Mary” to the HashSet.
You can remove elements from a HashSet object using the remove method. Here’s an example:
set.remove("Mary");In this example, we have removed the name “Mary” from the HashSet.
Iterating Over a HashSet
You can iterate over the elements in a HashSet object using a for loop or an iterator. Here’s an example using a for loop:
for (String name : set) {
System.out.println(name);
}In this example, we have used a for loop to iterate over the elements in the HashSet and print them to the console.
Checking for Element Existence
You can check if an element exists in a HashSet object using the contains method. Here’s an example:
boolean exists = set.contains("John");In this example, we have checked if the name “John” exists in the HashSet and stored the result in a boolean variable called exists.
Hashing and Equality
HashSet uses the hashCode and equals methods of the objects it contains to determine if two elements are equal. It uses the hashCode method to place elements in the hash table and the equals method to check for equality. For this reason, it is important to implement the hashCode and equals methods correctly in your objects if you plan to use them in a HashSet.
The HashSet class in Java provides a powerful and efficient way to store and manipulate groups of unique objects. By using the HashSet class, you can write code that can perform complex operations on the set efficiently and without worrying about duplicates.