Java String contains() Method

The String.contains() method in Java is used to check if a specified sequence of characters exists within a string.

Table of Contents

1. Introduction
2. contains Method Syntax
3. Examples
   • Basic Usage
   • Case Sensitivity
   • Using contains with Special Characters
   • Real-World Use Case
4. Conclusion

Introduction

The String.contains() method is a member of the String class in Java. It allows you to determine if a given substring is present within the string. This is particularly useful for searching and validation purposes.

contains() Method Syntax

The syntax for the contains method is as follows:

public boolean contains(CharSequence s)

• s: The sequence of characters to search for.

Examples

Basic Usage

The contains method can be used to check if a string contains a specified sequence of characters.

Example

public class ContainsExample {
    public static void main(String[] args) {
        String str = "Welcome to Java";
        boolean result = str.contains("Java");
        System.out.println("Contains 'Java': " + result);
    }
}

Output:

Contains 'Java': true

Case Sensitivity

The contains 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 str = "Welcome to Java";
        boolean result1 = str.contains("java");
        boolean result2 = str.contains("Java");
        System.out.println("Contains 'java': " + result1);
        System.out.println("Contains 'Java': " + result2);
    }
}

Output:

Contains 'java': false
Contains 'Java': true

Using contains with Special Characters

The contains method can also be used with strings containing special characters.

Example

public class SpecialCharactersExample {
    public static void main(String[] args) {
        String str = "Welcome to Java @2021!";
        boolean result = str.contains("@2021");
        System.out.println("Contains '@2021': " + result);
    }
}

Output:

Contains '@2021': true

Real-World Use Case

Example: Validating User Input

One common use case for contains is validating user input, such as checking if an email address contains the "@" symbol.

public class ValidateEmailExample {
    public static void main(String[] args) {
        String email = "user@example.com";
        if (email.contains("@")) {
            System.out.println("Valid email address.");
        } else {
            System.out.println("Invalid email address.");
        }
    }
}

Output:

Valid email address.

In this example, the contains method is used to check if the email address contains the "@" symbol, which is a basic validation step.

Conclusion

The String.contains() method in Java is used for checking if a specified sequence of characters is present within a string. It is case-sensitive and works with strings containing special characters. This method is particularly useful for searching and validating strings in various applications. By understanding and utilizing the contains method, you can efficiently manage string validation and searching in your Java programs.