Override equals Method in Java

In Java, you can override the equals() method from the Object class to provide your own implementation for comparing the equality of objects. The equals() method is used to compare two objects for equality.

To override the equals() method, you need to follow these steps:

• Open the class for which you want to override the equals() method.
• Add the following method signature to your class:

@Override

public boolean equals(Object obj) {

// Implement your code here

}

The @Override annotation is optional but recommended, as it ensures that you are actually overriding a method from the superclass.

Example 1

In the above example, we have a Person class with name and age instance variables. We override the equals() method to compare two Person objects based on both the name and age values.

FileName: EqualsOverrideExample.java

class Person {
 private String name; // variable to store the name of the person
 private int age; // variable to store the age of the person
 public Person(String name, int age) {
 this.name = name; // Assigning the provided name to the name instance variable
 this.age = age; // Assigning the provided age to the age instance variable
 }
 @Override
 public boolean equals(Object obj) {
 if (this == obj) {
 return true; // Same object reference, so they are equal
 }
 if (obj == null || getClass() != obj.getClass()) {
 return false; // obj is null or belongs to a different class, so they are not equal
 }
 Person other = (Person) obj; // Casting obj to Person type
 return this.name.equals(other.name) && this.age == other.age; // Comparing name and age for equality
 }
}
class EqualsOverrideExample {
 public static void main(String[] args) {
 Person person1 = new Person("Ram", 32);
 Person person2 = new Person("Ram", 32);
 Person person3 = new Person("Sham", 11);
 System.out.println(person1.equals(person2));
 System.out.println(person1.equals(person3));
 }
}

Output

true
false

Example 2:

In the above program, we have created a Car class with brand, model, and year instance variables. We override the equals() method to compare two Car objects based on all three variables.

FileName: EqualsOverrideExample.java

class Car {
 private String brand;
 private String model;
 private int year;
 public Car(String brand, String model, int year) {
 this.brand = brand;
 this.model = model;
 this.year = year;
 }
 @Override
 public boolean equals(Object obj) {
 if (this == obj) {
 return true; // Same object reference, so they are equal
 }
 if (obj == null || getClass() != obj.getClass()) {
 return false; // obj is null or belongs to a different class, so they are not equal
 }
 Car other = (Car) obj; // Casting obj to Car type
 return this.brand.equals(other.brand) &&
 this.model.equals(other.model) &&
 this.year == other.year; // Comparing brand, model, and year for equality
 }
}
class EqualsOverrideExample {
 public static void main(String[] args) {
 Car car1 = new Car("Toyota", "Camry", 2021);
 Car car2 = new Car("Toyota", "Camry", 2021);
 Car car3 = new Car("Honda", "Civic", 2020);
 System.out.println(car1.equals(car2));
 System.out.println(car1.equals(car3));
 }
}

Output

true
false

Example 3

In this example, we have a Book class with title, author, and year instance variables. We override the equals() method to compare two Book objects based on all three variables. In the main() method, we create three Book objects: book1, book2, and book3. We then use the equals() method to compare book1 with book2 and book1 with book3. The program outputs true for the first comparison (since all variables are the same), and false for the second comparison (since the title and author are different).

FileName: EqualsOverrideExample.java

class Book {
 private String title;
 private String author;
 private int year;
 public Book(String title, String author, int year) {
 this.title = title;
 this.author = author;
 this.year = year;
 }
 @Override
 public boolean equals(Object obj) {
 if (this == obj) {
 return true; // Same object reference, so they are equal
 }
 if (obj == null || getClass() != obj.getClass()) {
 return false; // obj is null or belongs to a different class, so they are not equal
 }
 Book other = (Book) obj; // Casting obj to Book type
 return this.title.equals(other.title) &&
 this.author.equals(other.author) &&
 this.year == other.year; // Comparing title, author, and year for equality
 }
}
class EqualsOverrideExample {
 public static void main(String[] args) {
 Book book1 = new Book("Adiyogi", "Sadhguru", 2011);
 Book book2 = new Book("Adiyogi", "Sadhguru", 2011);
 Book book3 = new Book("Wings of Fire", "APJ abdul kalam", 1990);
 System.out.println(book1.equals(book3));
 System.out.println(book1.equals(book2));
 }
}

Output

false
true