Java: Check If String Contains Substring

🎓 Top 15 Udemy Courses (80-90% Discount): My Udemy Courses - Ramesh Fadatare — All my Udemy courses are real-time and project oriented courses.

▶️ Subscribe to My YouTube Channel (178K+ subscribers): Java Guides on YouTube

▶️ For AI, ChatGPT, Web, Tech, and Generative AI, subscribe to another channel: Ramesh Fadatare on YouTube

In Java, checking if a string contains a specific substring is a common task. This can be done using various methods, each suited to different scenarios. This guide will cover different ways to check if a string contains a substring, including using the contains method, indexOf method, matches method with regular expressions and Pattern and Matcher classes.

Table of Contents

1. Introduction
2. Using String.contains Method
3. Using String.indexOf Method
4. Using String.matches Method with Regular Expressions
5. Using Pattern and Matcher Classes
6. Conclusion

Introduction

Strings in Java are sequences of characters used to represent text. Checking if a string contains a specific substring can be done using various methods, each with its own advantages and use cases.

Using String.contains Method

The contains method checks if a string contains a specified sequence of characters.

Example

public class SubstringCheckExample {
    public static void main(String[] args) {
        String str = "Hello, world!";
        String substr1 = "world";
        String substr2 = "Java";

        System.out.println(containsSubstring(str, substr1)); // true
        System.out.println(containsSubstring(str, substr2)); // false
    }

    public static boolean containsSubstring(String str, String substr) {
        return str.contains(substr);
    }
}

Explanation

• str.contains(substr): Returns true if str contains substr, false otherwise.

Using String.indexOf Method

The indexOf method returns the index within the string of the first occurrence of the specified substring, or -1 if the substring is not found.

Example

public class SubstringCheckExample {
    public static void main(String[] args) {
        String str = "Hello, world!";
        String substr1 = "world";
        String substr2 = "Java";

        System.out.println(containsSubstring(str, substr1)); // true
        System.out.println(containsSubstring(str, substr2)); // false
    }

    public static boolean containsSubstring(String str, String substr) {
        return str.indexOf(substr) != -1;
    }
}

Explanation

• str.indexOf(substr) != -1: Returns true if str contains substr, false otherwise.

Using String.matches Method with Regular Expressions

The matches method can be used with regular expressions to check if a string contains a substring. However, this method is generally used for full string matching rather than partial matching.

Example

public class SubstringCheckExample {
    public static void main(String[] args) {
        String str = "Hello, world!";
        String substr1 = "world";
        String substr2 = "Java";

        System.out.println(containsSubstring(str, substr1)); // true
        System.out.println(containsSubstring(str, substr2)); // false
    }

    public static boolean containsSubstring(String str, String substr) {
        return str.matches(".*" + substr + ".*");
    }
}

Explanation

• str.matches(".*" + substr + ".*"): Uses a regular expression to check if str contains substr. The .* before and after the substring allows for any characters to be present before or after the substring.

Using Pattern and Matcher Classes

The Pattern and Matcher classes from the java.util.regex package provide more flexibility and control when working with regular expressions.

Example

import java.util.regex.Matcher;
import java.util.regex.Pattern;

public class SubstringCheckExample {
    public static void main(String[] args) {
        String str = "Hello, world!";
        String substr1 = "world";
        String substr2 = "Java";

        System.out.println(containsSubstring(str, substr1)); // true
        System.out.println(containsSubstring(str, substr2)); // false
    }

    public static boolean containsSubstring(String str, String substr) {
        Pattern pattern = Pattern.compile(Pattern.quote(substr));
        Matcher matcher = pattern.matcher(str);
        return matcher.find();
    }
}

Explanation

• Pattern.compile(Pattern.quote(substr)): Compiles the regular expression. Pattern.quote is used to escape any special characters in the substring.
• matcher.find(): Returns true if the substring is found in the string, false otherwise.

Conclusion

Checking if a string contains a substring in Java can be accomplished using various methods, including the contains method, indexOf method, matches method with regular expressions, and the Pattern and Matcher classes. Each method has its own advantages and specific use cases:

• The contains method is straightforward and easy to use.
• The indexOf method is useful if you also need the index of the substring.
• The matches method with regular expressions provides a way to use regex for substring checks, though it's more commonly used for full string matching.
• The Pattern and Matcher classes provide a flexible and powerful way to work with regular expressions, especially for complex patterns.

By understanding these methods, you can choose the most appropriate one for your specific use case when working with strings in Java.

My Top and Bestseller Udemy Courses. The sale is going on with a 70 - 80% discount. The discount coupon has been added to each course below:

Build REST APIs with Spring Boot 4, Spring Security 7, and JWT

🆕 High-Demand 80–90% OFF

[NEW] Learn Apache Maven with IntelliJ IDEA and Java 25

🆕 High-Demand 80–90% OFF

ChatGPT + Generative AI + Prompt Engineering for Beginners

🚀 Trending Now 80–90% OFF

Spring 7 and Spring Boot 4 for Beginners (Includes 8 Projects)

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Building Real-Time REST APIs with Spring Boot - Blog App

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Building Microservices with Spring Boot and Spring Cloud

🌟 Top Rated 80–90% OFF
Available in Udemy for Business

Java Full-Stack Developer Course with Spring Boot and React JS

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Build 5 Spring Boot Projects with Java: Line-by-Line Coding

🌟 Top Rated 80–90% OFF

Testing Spring Boot Application with JUnit and Mockito

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Spring Boot Thymeleaf Real-Time Web Application - Blog App

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Master Spring Data JPA with Hibernate

🔥 Bestseller 80–90% OFF
Available in Udemy for Business

Spring Boot + Apache Kafka Course - The Practical Guide

🎓 Student Favorite 80–90% OFF
Available in Udemy for Business

Java Testing: Mastering JUnit 5 Framework

🆕 New 80–90% OFF

Reactive Programming in Java: Spring WebFlux and Testing

🌟 Top Rated 80–90% OFF

Spring Boot + RabbitMQ Course - The Practical Guide

🌟 Top Rated 80–90% OFF
Available in Udemy for Business

Functional Programming in Java (Includes Java Collections)

🎓 Student Favorite 80–90% OFF

ChatGPT for Java Developers: Boost Your Productivity with AI

🚀 Trending Now 80–90% OFF