Java Stream concat()

🎓 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 this guide, you will learn about the Stream concat() method in Java programming and how to use it with an example.

1. Stream concat() Method Overview

Definition:

The Stream.concat() method is a static utility method that is used to concatenate two streams into a single stream. The resulting stream will contain elements from both input streams in the order they appear.

Syntax:

static <T> Stream<T> concat(Stream<? extends T> a, Stream<? extends T> b)

Parameters:

- a: the first stream.

- b: the second stream.

Key Points:

- It's a static method and does not operate on a stream instance.

- It is an intermediate operation, meaning the concatenation does not happen immediately. Instead, the operation is executed only when a terminal operation is invoked on the concatenated stream.

- If either stream is parallel, the resulting stream is also parallel.

- Closing the concatenated stream closes both input streams.

- Concatenation is lazy, meaning elements are consumed from the input streams as they are required.

- Care should be taken when using infinite streams with concat, as it can lead to unintended infinite sequences.

2. Stream concat() Method Example

import java.util.stream.Stream;

public class StreamConcatExample {
    public static void main(String[] args) {
        Stream<String> fruitsStream = Stream.of("Apple", "Banana", "Cherry");
        Stream<String> veggiesStream = Stream.of("Artichoke", "Broccoli", "Carrot");

        // Concatenate the two streams
        Stream<String> concatenatedStream = Stream.concat(fruitsStream, veggiesStream);

        // Print the concatenated stream
        concatenatedStream.forEach(System.out::println);
    }
}

Output:

Apple
Banana
Cherry
Artichoke
Broccoli
Carrot

Explanation:

In the provided example: 

We have two streams, one containing fruit names and another containing vegetable names. 

Using Stream.concat(), we concatenate these two streams into a single stream. 

We then print the concatenated stream, which first displays fruits followed by vegetables.

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