Java Code Example: advanced HashSet example

This code defines a custom Person class with a name and an age, and implements the equals() and hashCode() methods to ensure that HashSet considers two Person objects equal if they have the same name and age.

The code creates a HashSet of Person objects and adds three elements to it. It then tries to add a fourth element with the same name and age as the first element, but since it’s a duplicate, it’s not added to the HashSet. The code then prints out the contents of the HashSet, checks if a Person object with a certain name and age is present in the HashSet, removes a Person object from the HashSet, and prints out the contents of the HashSet again.

import java.util.HashSet;

class Person {
    private String name;
    private int age;

    public Person(String name, int age) { = name;
        this.age = age;

    public String getName() {
        return name;

    public int getAge() {
        return age;

    // Implementing equals() and hashCode() methods
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;

        Person person = (Person) o;

        if (age != person.age) return false;
        return name != null ? name.equals( : == null;

    public int hashCode() {
        int result = name != null ? name.hashCode() : 0;
        result = 31 * result + age;
        return result;

    public String toString() {
        return "Person{" +
                "name='" + name + '\'' +
                ", age=" + age +

public class AdvancedHashSetExample {
    public static void main(String[] args) {
        HashSet<Person> set = new HashSet<>();

        // Adding elements to the HashSet
        set.add(new Person("Alice", 25));
        set.add(new Person("Bob", 30));
        set.add(new Person("Charlie", 35));
        set.add(new Person("Alice", 25)); // This will not be added to the HashSet because it is a duplicate

        // Printing the HashSet

        // Checking if an element is present in the HashSet
        Person alice = new Person("Alice", 25);
        if (set.contains(alice)) {
            System.out.println("The HashSet contains " + alice);
        } else {
            System.out.println("The HashSet does not contain " + alice);

        // Removing an element from the HashSet
        set.remove(new Person("Bob", 30));

        // Printing the HashSet after removing an element