Java String equals() Method

The String.equals() method in Java is used to compare two strings for equality.

Table of Contents

1. Introduction
2. equals Method Syntax
3. Examples
   • Basic Usage
   • Case Sensitivity
   • Using equals with Null Values
   • Real-World Use Case
4. Conclusion

Introduction

The String.equals() method is a member of the String class in Java. It compares the specified string to the current string, checking if they have the same sequence of characters. This comparison is case-sensitive, meaning "Hello" and "hello" are considered different strings.

equals() Method Syntax

The syntax for the equals method is as follows:

public boolean equals(Object anObject)

• anObject: The object to compare with.

Examples

Basic Usage

The equals method can be used to compare two strings for equality.

Example

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

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

        System.out.println("str1 equals str2: " + result1); // Output: true
        System.out.println("str1 equals str3: " + result2); // Output: false
    }
}

Output:

str1 equals str2: true
str1 equals str3: false

Case Sensitivity

The equals method is case-sensitive, meaning it will only return true if the exact sequence, including case, is found.

Example

public class CaseSensitiveExample {
    public static void main(String[] args) {
        String str1 = "Hello";
        String str2 = "hello";

        boolean result = str1.equals(str2);

        System.out.println("str1 equals str2 (case-sensitive): " + result); // Output: false
    }
}

Output:

str1 equals str2 (case-sensitive): false

Using equals with Null Values

When comparing strings, it is important to handle null values to avoid NullPointerException.

Example

public class EqualsNullExample {
    public static void main(String[] args) {
        String str1 = "Hello";
        String str2 = null;

        boolean result = str1.equals(str2);

        System.out.println("str1 equals str2: " + result); // Output: false
    }
}

Output:

str1 equals str2: false

Example: Safe Comparison

To safely compare a string with a potential null value, use a static string to call equals.

public class SafeEqualsExample {
    public static void main(String[] args) {
        String str1 = null;
        String str2 = "Hello";

        boolean result = "Hello".equals(str1);
        boolean result2 = "Hello".equals(str2);

        System.out.println("Safe comparison with str1: " + result); // Output: false
        System.out.println("Safe comparison with str2: " + result2); // Output: true
    }
}

Output:

Safe comparison with str1: false
Safe comparison with str2: true

Real-World Use Case

Example: Validating User Input

One common use case for equals is validating user input, such as checking if a username matches an expected value.

public class ValidateUserExample {
    public static void main(String[] args) {
        String expectedUsername = "admin";
        String inputUsername = "Admin";

        if (expectedUsername.equals(inputUsername)) {
            System.out.println("Access granted.");
        } else {
            System.out.println("Access denied.");
        }
    }
}

Output:

Access denied.

In this example, the equals method is used to check if the input username matches the expected username exactly.

Conclusion

The String.equals() method in Java is a fundamental tool for comparing strings. It performs a case-sensitive comparison and returns true if the strings are identical in terms of character sequence and case. This method is particularly useful for validation and comparison tasks in various applications. By understanding and utilizing the equals method, you can efficiently manage string comparisons in your Java programs.