How can I turn a List of Lists into a List in Java 8?

📝 Title: Unleash the Magic of Java 8: Converting a List of Lists to a List

🥳 Introduction:

Welcome, tech enthusiasts, to yet another exciting dive into the world of Java 8! 🚀 Today, we'll embark on a quest to transform a tricky problem into a seamless solution. Imagine having a List of Lists, and you need to convert it into a regular List using the phenomenal features of Java 8. 🤔 Fear not, for we shall conquer this challenge together!

🔍 The Problem at Hand:

So, you have a List<List<Object>>. How can you transform this nested list structure into a flat List<Object> while preserving the order of its elements? 🤷‍♂️ This requirement often arises in scenarios where you need to process data conveniently or perform further operations on a single list.

💡 The Brilliant Solution:

Hold on tight, folks! Java 8 brings an elegant solution to our fingertips. Let's explore three ingenious ways to resolve this predicament.

1️⃣ Using Stream.flatMap():

By utilizing the Stream API and its marvelous flatMap() function, we can whiz past this problem in a single line of code! Take a look at this snippet:

List<Object> flatList = listOfLists.stream()
                                   .flatMap(List::stream)
                                   .collect(Collectors.toList());

The flatMap() function unleashes its enchanting powers by flattening each inner List into a stream of objects. We then collect these objects into a new List using the trusted Collectors.toList() collector.

2️⃣ Tackling it with Stream.reduce():

For those seeking an alternative approach, Java 8's Stream API bestows upon us another powerful sorcery: reduce(). This method collapses a stream into a single result. Behold the magic unfold:

List<Object> flatList = listOfLists.stream()
                                   .reduce(new ArrayList<>(), (list1, list2) -> {
                                        list1.addAll(list2);
                                        return list1;
                                    });

Using the reduce() function, we seamlessly merge each inner List into a single result List. We start with an empty ArrayList and continually accumulate our desired output.

3️⃣ Through Apache Commons Collections:

For those who prefer the enchantment of third-party libraries, Apache Commons Collections offers us its mystical powers. By using the ListUtils.union() function, we can merge the inner lists and effortlessly turn them into one:

import org.apache.commons.collections4.ListUtils;

List<Object> flatList = ListUtils.union(listOfLists.get(0), listOfLists.get(1));

📣 The Call-to-Action:

Now that you've witnessed the sorcery of converting a List of Lists into a regular List with the wondrous tools of Java 8, it's time for you to weave your own spells! ✨ Experiment with different scenarios, explore additional Java 8 features, and share your newfound knowledge with the world. Engage with us in the comments below and let us know which technique resonated most with you. 📢

So what are you waiting for? 🎩 Let the magic begin! 🧙‍♀️✨