Massimo Caliman
by Massimo Caliman
1 min read


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  • Java


  • Java
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The hashCode method is a fundamental method of the Object class in Java. This method returns an integer value representing the hash code of the object.

The hashCode method is mainly used to improve the performance of hash-based data structures, such as HashMaps. When you insert an object into a HashMap, its hash code is used to determine the location where the object should be stored in the map.

To use the hashCode method correctly, it is important to follow some rules. First, the hashCode method must be appropriately overridden in subclasses. Additionally, if two objects are equal according to the equals method, then they must return the same hash code value.

Here is an example of how to override the hashCode method in a subclass:

public class Human {
    private String firstName;
    private String lastName;
    private String passportNumber;

    public Human(String firstName, String lastName, String passportNumber) {
        this.firstName = firstName;
        this.lastName = lastName;
        this.passportNumber = passportNumber;

    public int hashCode() {
        return Objects.hash(firstName, lastName, passportNumber);

In this example, we have overridden the hashCode method in the Human class to calculate the hash code of a Human object based on its firstName, lastName, and passportNumber attributes.

Always remember to use the hashCode method correctly when working with objects in Java!