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Java Object hashCode()
What is a Object in Java?
Java is an object-oriented programming language, which means that it is based on the concepts of classes and objects. The properties of an object are represented by its fields or instance variables, and the behavior of an object is represented by its methods.
In Java, an object is an instance of a class. A class is a blueprint or template that defines the properties and methods of an object. An object is created from a class and can be used to access the properties and methods of that class.
- An object in Java is created using the new keyword, followed by the class name and constructor.
To know more about Object toString in java read the complete article.
Object tostring() method.
In Java, the hashCode() method is a method that is defined in the Object class, which is the parent class of all classes in Java. It returns an integer value that represents the unique hash code of an object. The hash code is a unique identifier for an object, and it is used by certain collection classes, such as HashMap and HashSet, to efficiently store and retrieve objects.
- The hashCode() method is based on the memory address of the object, but it can be overridden by subclasses to provide a more meaningful hash code that is based on the state of the object. For example, if you have a class called Person with fields for a name and age, you could override the hashCode() method to return a hash code that is based on the name and age of the person.
Returns
returns the hash code value of the object
Note:
The general form of hashCode() method is public int hashCode().
Syntax:
object.hashCode()
Parameters:
The hashCode() method does not take any parameters.
Let’s look at a object-related Java program where the Java object hashcode Method is used to perform an operation on the given string.
Example: Java Object hashcode() Method
class Animal {
private String species;
private int weight;
private int age;
public Animal(String species, int weight, int age) {
this.species = species;
this.weight = weight;
this.age = age;
}
@Override
public int hashCode() {
int result = 17;
result = 31 * result + species.hashCode();
result = 31 * result + weight;
result = 31 * result + age;
return result;
}
}
public class Main {
public static void main(String[] args) {
Animal animal1 = new Animal("Lion", 200, 12);
Animal animal2 = new Animal("Elephant", 600, 20);
System.out.println("Hashcode for animal1: " + animal1.hashCode());
System.out.println("Hashcode for animal2: " + animal2.hashCode());
}
}
Output
Hashcode for animal1: -2018256945 Hashcode for animal2: 1011192316
Explanation:
In this example, the Animal class has three fields, species, weight, and age, and a constructor that initializes these fields. The hashCode() method is overridden to return a hash code that is based on the species, weight and age of the animal. The calculation of the hash code is done using the species.hashCode(), weight and age fields.
The main class creates two instances of the Animals class, animal1 and animal2, each with its own unique species, weight, and age. The hashCode() method is called on each object, which returns a unique hash code for each object based on the species, weight, and age.
Example 2 : Java object hashcode() Method
class Car {
private String make;
private String model;
private int year;
public Car(String make, String model, int year) {
this.make = make;
this.model = model;
this.year = year;
}
@Override
public int hashCode() {
int result = 17;
result = 31 * result + make.hashCode();
result = 31 * result + model.hashCode();
result = 31 * result + year;
return result;
}
}
public class Main {
public static void main(String[] args) {
Car car1 = new Car("Honda", "Civic", 2020);
Car car2 = new Car("Toyota", "Corolla", 2022);
System.out.println("Hashcode for car1: " + car1.hashCode());
System.out.println("Hashcode for car2: " + car2.hashCode());
}
}
Output
Hashcode for car1: 482534285 Hashcode for car2: -1021003685
Explanation:
In this example, the Car class has three fields, make, model, and year, and a constructor that initializes these fields. The hashCode() method is overridden to return a hash code that is based on the make, model, and year of the car. The calculation of the hash code is done using the make.hashCode(), model.hashCode() and year fields.
The main class creates two instances of the Car class, car1 and car2, each with its own unique make, model, and year. The hashCode() method is called on each object, which returns a unique hash code for each object based on the make, model
Example 3: how to use the object hashcode property:
class Person {
private String name;
private int age;
public Person(String name, int age) {
this.name = name;
this.age = age;
}
@Override
public int hashCode() {
int result = 17;
result = 31 * result + name.hashCode();
result = 31 * result + age;
return result;
}
}
public class Main {
public static void main(String[] args) {
Person person1 = new Person("John", 30);
Person person2 = new Person("Jane", 25);
System.out.println("Hashcode for person1: " + person1.hashCode());
System.out.println("Hashcode for person2: " + person2.hashCode());
}
}
Output
Hashcode for person1: 71767076 Hashcode for person2: 71355484
Explanation:
In this example, the Person class has two fields, name and age, and a constructor that initializes these fields. The toString() method is overridden to return a string representation of the Person object that includes the name and age of the person.
The main class creates two instances of the Person class, person1 and person2, each with its own unique name and age. The toString() method is called on each object, which returns a string representation of the object that includes the name and age.
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