Who is this book for?

If you can answer “yes” to all of these:

1. Have you done some programming?

2. Do you want to learn Kotlin?

3. Do you prefer actually doing things and applying the stuff you learn over listening to someone in a lecture rattle on for hours on end?

this book is for you.

Who should probably back away from this book?

If you can answer “yes” to any of these:

1. Is your programming background limited to HTML only, with no scripting language experience?

   (If you’ve done anything with looping, or if/then logic, you’ll do fine with this book, but HTML tagging alone might not be enough.)

2. Are you a kick-butt Kotlin programmer looking for a reference book?

3. Would you rather have your toenails pulled out by 15 screaming monkeys than learn something new? Do you believe a Kotlin book should cover everything, especially all the obscure stuff you’ll never use, and if it bores the reader to tears in the process, then so much the better?

this book is not for you.

Note

[Note from Marketing: this book is for anyone with a credit card or a PayPal account]

We know what you’re thinking

“How can this be a serious Kotlin book?”

“What’s with all the graphics?”

“Can I actually learn it this way?”

“Do I smell pizza?”

We know what your brain is thinking

Your brain craves novelty. It’s always searching, scanning, waiting for something unusual. It was built that way, and it helps you stay alive.

So what does your brain do with all the routine, ordinary, normal things you encounter? Everything it can to stop them from interfering with the brain’s real job—recording things that matter. It doesn’t bother saving the boring things; they never make it past the “this is obviously not important” filter.

How does your brain know what’s important? Suppose you’re out for a day hike and a tiger jumps in front of you—what happens inside your head and body?

Neurons fire. Emotions crank up. Chemicals surge.

And that’s how your brain knows…

This must be important! Don’t forget it!

But imagine you’re at home or in a library. It’s a safe, warm, tiger-free zone. You’re studying. Getting ready for an exam. Or trying to learn some tough technical topic your boss thinks will take a week, ten days at the most.

Just one problem. Your brain’s trying to do you a big favor. It’s trying to make sure that this obviously unimportant content doesn’t clutter up scarce resources. Resources that are better spent storing the really big things. Like tigers. Like the danger of fire. Like how you should never have posted those party photos on your Facebook page. And there’s no simple way to tell your brain, “Hey brain, thank you very much, but no matter how dull this book is, and how little I’m registering on the emotional Richter scale right now, I really do want you to keep this stuff around.”

Metacognition: thinking about thinking

If you really want to learn, and you want to learn more quickly and more deeply, pay attention to how you pay attention. Think about how you think. Learn how you learn.

Most of us did not take courses on metacognition or learning theory when we were growing up. We were expected to learn, but rarely taught to learn.

But we assume that if you’re holding this book, you really want to learn how to code in Kotlin. And you probably don’t want to spend a lot of time. If you want to use what you read in this book, you need to remember what you read. And for that, you’ve got to understand it. To get the most from this book, or any book or learning experience, take responsibility for your brain. Your brain on this content.

The trick is to get your brain to see the new material you’re learning as Really Important. Crucial to your well-being. As important as a tiger. Otherwise, you’re in for a constant battle, with your brain doing its best to keep the new content from sticking.

So just how DO you get your brain to treat Kotlin like it was a hungry tiger?

There’s the slow, tedious way, or the faster, more effective way. The slow way is about sheer repetition. You obviously know that you are able to learn and remember even the dullest of topics if you keep pounding the same thing into your brain. With enough repetition, your brain says, “This doesn’t feel important to him, but he keeps looking at the same thing over and over and over, so I suppose it must be.”

The faster way is to do anything that increases brain activity, especially different types of brain activity. The things on the previous page are a big part of the solution, and they’re all things that have been proven to help your brain work in your favor. For example, studies show that putting words within the pictures they describe (as opposed to somewhere else in the page, like a caption or in the body text) causes your brain to try to makes sense of how the words and picture relate, and this causes more neurons to fire. More neurons firing = more chances for your brain to get that this is something worth paying attention to, and possibly recording.

A conversational style helps because people tend to pay more attention when they perceive that they’re in a conversation, since they’re expected to follow along and hold up their end. The amazing thing is, your brain doesn’t necessarily care that the “conversation” is between you and a book! On the other hand, if the writing style is formal and dry, your brain perceives it the same way you experience being lectured to while sitting in a roomful of passive attendees. No need to stay awake.

But pictures and conversational style are just the beginning…

Here’s what WE did:

We used pictures, because your brain is tuned for visuals, not text. As far as your brain’s concerned, a picture really is worth a thousand words. And when text and pictures work together, we embedded the text in the pictures because your brain works more effectively when the text is within the thing it refers to, as opposed to in a caption or buried in the body text somewhere.

We used redundancy, saying the same thing in different ways and with different media types, and multiple senses, to increase the chance that the content gets coded into more than one area of your brain.

We used concepts and pictures in unexpected ways because your brain is tuned for novelty, and we used pictures and ideas with at least some emotional content, because your brain is tuned to pay attention to the biochemistry of emotions. That which causes you to feel something is more likely to be remembered, even if that feeling is nothing more than a little humor, surprise, or interest.

We used a personalized, conversational style, because your brain is tuned to pay more attention when it believes you’re in a conversation than if it thinks you’re passively listening to a presentation. Your brain does this even when you’re reading.

We included activities, because your brain is tuned to learn and remember more when you do things than when you read about things. And we made the exercises challenging-yet-doable, because that’s what most people prefer.

We used multiple learning styles, because you might prefer step-by-step procedures, while someone else wants to understand the big picture first, and someone else just wants to see an example. But regardless of your own learning preference, everyone benefits from seeing the same content represented in multiple ways.

We include content for both sides of your brain, because the more of your brain you engage, the more likely you are to learn and remember, and the longer you can stay focused. Since working one side of the brain often means giving the other side a chance to rest, you can be more productive at learning for a longer period of time.

And we included stories and exercises that present more than one point of view, because your brain is tuned to learn more deeply when it’s forced to make evaluations and judgments.

We included challenges, with exercises, and by asking questions that don’t always have a straight answer, because your brain is tuned to learn and remember when it has to work at something. Think about it—you can’t get your body in shape just by watching people at the gym. But we did our best to make sure that when you’re working hard, it’s on the right things. That you’re not spending one extra dendrite processing a hard-to-understand example, or parsing difficult, jargon-laden, or overly terse text.

We used people. In stories, examples, pictures, etc., because, well, you’re a person. And your brain pays more attention to people than it does to things.

Here’s what YOU can do to bend your brain into submission

So, we did our part. The rest is up to you. These tips are a starting point; listen to your brain and figure out what works for you and what doesn’t. Try new things.

1. Slow down. The more you understand, the less you have to memorize.

   Don’t just read. Stop and think. When the book asks you a question, don’t just skip to the answer. Imagine that someone really is asking the question. The more deeply you force your brain to think, the better chance you have of learning and remembering.

2. Do the exercises. Write your own notes.

   We put them in, but if we did them for you, that would be like having someone else do your workouts for you. And don’t just look at the exercises. Use a pencil. There’s plenty of evidence that physical activity while learning can increase the learning.

3. Read “There Are No Dumb Questions.”

   That means all of them. They’re not optional sidebars, they’re part of the core content! Don’t skip them.

4. Make this the last thing you read before bed. Or at least the last challenging thing.

   Part of the learning (especially the transfer to long-term memory) happens after you put the book down. Your brain needs time on its own, to do more processing. If you put in something new during that processing time, some of what you just learned will be lost.

5. Talk about it. Out loud.

   Speaking activates a different part of the brain. If you’re trying to understand something, or increase your chance of remembering it later, say it out loud. Better still, try to explain it out loud to someone else. You’ll learn more quickly, and you might uncover ideas you hadn’t known were there when you were reading about it.

6. Drink water. Lots of it.

   Your brain works best in a nice bath of fluid. Dehydration (which can happen before you ever feel thirsty) decreases cognitive function.

7. Listen to your brain.

   Pay attention to whether your brain is getting overloaded. If you find yourself starting to skim the surface or forget what you just read, it’s time for a break. Once you go past a certain point, you won’t learn faster by trying to shove more in, and you might even hurt the process.

8. Feel something.

   Your brain needs to know that this matters. Get involved with the stories. Make up your own captions for the photos. Groaning over a bad joke is still better than feeling nothing at all.

9. Write a lot of code!

   There’s only one way to learn Kotlin: write a lot of code. And that’s what you’re going to do throughout this book. Coding is a skill, and the only way to get good at it is to practice. We’re going to give you a lot of practice: every chapter has exercises that pose a problem for you to solve. Don’t just skip over them—a lot of the learning happens when you solve the exercises. We included a solution to each exercise—don’t be afraid to peek at the solution if you get stuck! (It’s easy to get snagged on something small.) But try to solve the problem before you look at the solution. And definitely get it working before you move on to the next part of the book.

Read me

This is a learning experience, not a reference book. We deliberately stripped out everything that might get in the way of learning whatever it is we’re working on at that point in the book. And the first time through, you need to begin at the beginning, because the book makes assumptions about what you’ve already seen and learned.

We assume you’re new to Kotlin, but not to programming.

We assume that you’ve already done some programming. Maybe not a lot, but we’ll assume you’ve already seen things like loops and variables in some other language. And unlike a lot of other Kotlin books, we don’t assume that you already know Java.

We begin by teaching some basic Kotlin concepts, and then we start putting Kotlin to work for you right away.

We cover the fundamentals of Kotlin code in Chapter 1. That way, by the time you make it all the way to Chapter 2, you are creating programs that actually do something. The rest of the book then builds on your Kotlin skills, turning you from Kotlin newbie to Kotlin ninja master in very little time.

The redundancy is intentional and important.

One distinct difference in a Head First book is that we want you to really get it. And we want you to finish the book remembering what you’ve learned. Most reference books don’t have retention and recall as a goal, but this book is about learning, so you’ll see some of the same concepts come up more than once.

The code examples are as lean as possible.

We know how frustrating it is to wade through 200 lines of code looking for the two lines you need to understand. Most examples within this book are shown within the smallest possible context, so that the part you’re trying to learn is clear and simple. So don’t expect the code to be robust, or even complete. That’s your assignment for after you finish the book, and it’s all part of the learning experience.

The exercises and activities are NOT optional.

The exercises and activities are not add-ons; they’re part of the core content of the book. Some of them are to help with memory, some are for understanding, and some will help you apply what you’ve learned. So don’t skip the exercises! Your brain will thank you for it.

The Brain Power exercises don’t have answers.

Not printed in the book, anyway. For some of them, there is no right answer, and for others, part of the learning experience is for you to decide if and when your answers are right. In some of the Brain Power exercises, you will find hints to point you in the right direction.

The technical review team

Technical reviewers:

Ingo Krotzky is a trained health information technician who has been working as a database programmer/software developer for contract research institutes.

Ken Kousen is the author of the books Modern Java Recipes (O’Reilly), Gradle Recipes for Android (O’Reilly) and Making Java Groovy (Manning), as well as O’Reilly video courses in Android, Groovy, Gradle, advanced Java and Spring. He is a regular speaker on the No Fluff, Just Stuff conference tour and a 2013 and 2016 JavaOne Rock Star, and has spoken at conferences all over the world. Through his company, Kousen I.T., Inc., he has taught software development training courses to thousands of students.

Acknowledgments

Our editor:

Heartfelt thanks to our awesome editor Jeff Bleiel for all his work and help. We’ve truly valued his trust, support, and encouragement. We’ve appreciated all the times he pointed out when things were unclear or needed a rethink, as it’s led to us writing a much better book.

The O’Reilly team:

A big thank you goes to Brian Foster for his early help in getting Head First Kotlin off the ground; Susan Conant, Rachel Roumeliotis and Nancy Davis for their help smoothing the wheels; Randy Comer for designing the cover; the early release team for making early versions of the book available for download; and Kristen Brown, Jasmine Kwityn, Lucie Haskins and the rest of the production team for expertly steering the book through the production process, and for working so hard behind the scenes.

Friends, family and colleagues:

Writing a Head First book is always a rollercoaster, and we’ve truly valued the kindness and support of our friends, family and colleagues along the way. Special thanks go to Jacqui, Ian, Vanessa, Dawn, Matt, Andy, Simon, Mum, Dad, Rob and Lorraine.

The without-whom list:

Our awesome technical review team worked hard to give us their thoughts on the book, and we’re so grateful for their input. They made sure that what we covered was spot on, and kept us entertained along the way. We think the book is much better as a result of their feedback.

Finally, our thanks to Kathy Sierra and Bert Bates for creating this extraordinary series of books, and for letting us into their brains.

O’Reilly

For almost 40 years, O’Reilly Media has provided technology and business training, knowledge, and insight to help companies succeed.

Our unique network of experts and innovators share their knowledge and expertise through books, articles, conferences, and our online learning platform. O’Reilly’s online learning platform gives you on-demand access to live training courses, in-depth learning paths, interactive coding environments, and a vast collection of text and video from O’Reilly and 200+ other publishers.

For more information, please visit http://oreilly.com.