Java Stream takeWhile()

🎓 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 takeWhile() method in Java programming and how to use it with an example.

1. Stream takeWhile() Method Overview

Definition:

The takeWhile() method of the Stream interface in Java is used to return elements from the stream as long as the given predicate holds true. Once an element fails to match the predicate, the operation stops and the elements after that are not included in the resulting stream.

Syntax:

Stream<T> takeWhile(Predicate<? super T> predicate)

Parameters:

- predicate: A non-interfering, stateless predicate to apply to elements of the stream, which returns true if the element should be included in the result.

Key Points:

- Introduced in Java 9.

- This is a short-circuiting stateful intermediate operation.

- The operation stops as soon as the predicate returns false or the end of the stream is reached.

- If the stream is unordered, any subset of the elements satisfying the predicate may be returned.

- For ordered streams, the returned stream is also ordered.

2. Stream takeWhile() Method Example

import java.util.stream.Stream;

public class TakeWhileExample {
    public static void main(String[] args) {
        // Creating a Stream of integers
        Stream<Integer> numberStream = Stream.of(2, 4, 6, 8, 9, 10, 12);

        // Using takeWhile() to return elements as long as they are even
        Stream<Integer> resultStream = numberStream.takeWhile(number -> number % 2 == 0);

        // Displaying the result
        resultStream.forEach(System.out::println);
    }
}

Output:

2
4
6
8

Explanation:

In the example, we have a Stream of integers. We use the takeWhile() method to take elements from the stream as long as they are even. As soon as the method encounters the number 9, which is not even, the operation stops, and the remaining elements are not included in the resulting stream. 

The output of the program demonstrates this, showing only the even numbers before the first odd number in the original stream.

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