Java Objects equals() Method

The Objects.equals() method in Java, part of the java.util.Objects class, is used to determine whether two objects are equal. This method is a utility for null-safe comparison, meaning it handles null values gracefully.

Table of Contents

1. Introduction
2. equals() Method Syntax
3. Understanding equals()
4. Examples
   • Basic Usage
   • Comparing with Null Values
5. Real-World Use Case
6. Conclusion

Introduction

The equals() method returns true if the two specified objects are equal to each other, and false otherwise. It uses the equals() method of the first object to determine equality, handling null values to avoid NullPointerException.

equals() Method Syntax

The syntax for the equals() method is as follows:

public static boolean equals(Object a, Object b)

Parameters:

• a: The first object to be compared.
• b: The second object to be compared.

Returns:

• true if the arguments are equal to each other; false otherwise.

Understanding equals()

The equals() method checks for equality by using the equals() method of the first object. If both objects are null, it returns true. If one of the objects is null, it returns false. If neither object is null, it uses the equals() method of the first object to compare them.

Examples

Basic Usage

To demonstrate the basic usage of equals(), we will compare two strings for equality.

Example

import java.util.Objects;

public class EqualsExample {
    public static void main(String[] args) {
        String str1 = "hello";
        String str2 = "hello";
        String str3 = "world";

        boolean result1 = Objects.equals(str1, str2);
        boolean result2 = Objects.equals(str1, str3);

        System.out.println("str1 and str2 are equal: " + result1);
        System.out.println("str1 and str3 are equal: " + result2);
    }
}

Output:

str1 and str2 are equal: true
str1 and str3 are equal: false

Comparing with Null Values

This example shows how to compare objects when one or both of them are null.

Example

import java.util.Objects;

public class NullComparisonExample {
    public static void main(String[] args) {
        String str1 = "hello";
        String str2 = null;
        String str3 = null;

        boolean result1 = Objects.equals(str1, str2);
        boolean result2 = Objects.equals(str2, str3);

        System.out.println("str1 and str2 are equal: " + result1);
        System.out.println("str2 and str3 are equal: " + result2);
    }
}

Output:

str1 and str2 are equal: false
str2 and str3 are equal: true

Real-World Use Case

Comparing Custom Objects

In a real-world scenario, you might use the equals() method to compare custom objects for equality, ensuring that null values are handled correctly.

Example

import java.util.Objects;

class Person {
    private String name;
    private int age;

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

    @Override
    public boolean equals(Object o) {
        if (this == o) return true;
        if (o == null || getClass() != o.getClass()) return false;
        Person person = (Person) o;
        return age == person.age && Objects.equals(name, person.name);
    }

    @Override
    public int hashCode() {
        return Objects.hash(name, age);
    }
}

public class CustomObjectComparison {
    public static void main(String[] args) {
        Person person1 = new Person("Alice", 30);
        Person person2 = new Person("Alice", 30);
        Person person3 = new Person("Bob", 25);

        boolean result1 = Objects.equals(person1, person2);
        boolean result2 = Objects.equals(person1, person3);

        System.out.println("person1 and person2 are equal: " + result1);
        System.out.println("person1 and person3 are equal: " + result2);
    }
}

Output:

person1 and person2 are equal: true
person1 and person3 are equal: false

Conclusion

The Objects.equals() method in Java provides a way to compare two objects for equality in a null-safe manner. By using this method, you can ensure that null values are handled gracefully, avoiding NullPointerException. 

Whether you are comparing simple data types or custom objects, the equals() method offers a reliable way to determine equality at runtime.