Download or read book Kotlin in Action written by Dmitry Jemerov and published by Simon and Schuster. This book was released on 2017-02-03 with total page 532 pages. Available in PDF, EPUB and Kindle. Book excerpt: Summary Kotlin in Action guides experienced Java developers from the language basics of Kotlin all the way through building applications to run on the JVM and Android devices. Foreword by Andrey Breslav, Lead Designer of Kotlin. Purchase of the print book includes a free eBook in PDF, Kindle, and ePub formats from Manning Publications. About the Technology Developers want to get work done - and the less hassle, the better. Coding with Kotlin means less hassle. The Kotlin programming language offers an expressive syntax, a strong intuitive type system, and great tooling support along with seamless interoperability with existing Java code, libraries, and frameworks. Kotlin can be compiled to Java bytecode, so you can use it everywhere Java is used, including Android. And with an effi cient compiler and a small standard library, Kotlin imposes virtually no runtime overhead. About the Book Kotlin in Action teaches you to use the Kotlin language for production-quality applications. Written for experienced Java developers, this example-rich book goes further than most language books, covering interesting topics like building DSLs with natural language syntax. The authors are core Kotlin developers, so you can trust that even the gnarly details are dead accurate. What's Inside Functional programming on the JVM Writing clean and idiomatic code Combining Kotlin and Java Domain-specific languages About the Reader This book is for experienced Java developers. About the Author Dmitry Jemerov and Svetlana Isakova are core Kotlin developers at JetBrains. Table of Contents PART 1 - INTRODUCING KOTLIN Kotlin: what and why Kotlin basics Defining and calling functions Classes, objects, and interfaces Programming with lambdas The Kotlin type system PART 2 - EMBRACING KOTLIN Operator overloading and other conventions Higher-order functions: lambdas as parameters and return values Generics Annotations and reflection DSL construction

Download or read book Atomic Kotlin written by Bruce Eckel and published by . This book was released on 2021-01-11 with total page 636 pages. Available in PDF, EPUB and Kindle. Book excerpt: For both beginning and experienced programmers! From the author of the multi-award-winning Thinking in C++ and Thinking in Java together with a member of the Kotlin language team comes a book that breaks the concepts into small, easy-to-digest "atoms," along with exercises supported by hints and solutions directly inside IntelliJ IDEA! No programming background necessary. Summaries for experienced programmers. Easy steps via very small chapters ("atoms"). Free accompanying exercises/solutions within IntelliJ Idea. Gives you a strong Kotlin foundation. Kotlin is cleaner, more consistent and far more powerful than Java. Increase programming productivity with Kotlin's clear, concise syntax. Produce safer, more reliable programs. Kotlin easily interacts with Java. Effortlessly migrate by adding pieces of Kotlin to an existing Java project. Support for Windows, Mac and Linux. Free version of Intellij IDEA includes extensive Kotlin support. Book resources, live seminars, workshops and consulting available at AtomicKotlin.com.

Download or read book Kotlin Quick Start Guide written by Marko Devcic and published by Packt Publishing Ltd. This book was released on 2018-08-31 with total page 172 pages. Available in PDF, EPUB and Kindle. Book excerpt: Get started with Kotlin programming for building real world applications Key Features Start programming with Kotlin Explore Kotlin language syntax, standard libraries and Java Interoperability Builds an example application with what you learn Book Description Kotlin is a general purpose, object-oriented language that primarily targets the JVM and Android. Intended as a better alternative to Java, its main goals are high interoperability with Java and increased developer productivity. Kotlin is still a new language and this book will help you to learn the core Kotlin features and get you ready for developing applications with Kotlin. This book covers Kotlin features in detail and explains them with practical code examples.You will learn how to set up the environment and take your frst steps with Kotlin and its syntax. We will cover the basics of the language, including functions, variables, and basic data types. With the basics covered, the next chapters show how functions are first-class citizens in Kotlin and deal with the object-oriented side of Kotlin. You will move on to more advanced features of Kotlin. You will explore Kotlin's Standard Library and learn how to work with the Collections API. The book finishes by putting Kotlin in to practice, showing how to build a desktop app. By the end of this book, you will be confident enough to use Kotlin for your next project. What you will learn Programming in Kotlin language syntax, basic types, control ?ow, classes, and OOP Writing functions and functional programming in Kotlin Defning and importing from packages in Kotlin Running Kotlin on JVMs and Android runtimes Working with the Kotlin Standard Library and advanced features of Kotlin programming Setting up a Kotlin development environment with JetBrains tools Building real-world applications with Kotlin Who this book is for This book is intended for anybody who wants to learn the most important Kotlin features. No experience of Kotlin is expected.

Download or read book Learn Kotlin for Android Development written by Peter Späth and published by Apress. This book was released on 2019-05-30 with total page 508 pages. Available in PDF, EPUB and Kindle. Book excerpt: Build Android apps and learn the essentials of the popular Kotlin programming language and APIs. This book will teach you the key Kotlin skills and techniques important for creating your very own Android apps. Apart from introducing Kotlin programming, Learn Kotlin for Android Development stresses clean code principles and introduces object-oriented and functional programming as a starting point for developing Android apps. After reading and using this book, you'll have a foundation to take away and apply to your own Kotlin-based Android app development. You'll be able to write useful and efficient Kotlin-based apps for Android, using most of the features Kotlin as a language has to offer. What You Will Learn Build your first Kotlin app that runs on Android Work with Kotlin classes and objects for Android Use constructs, loops, decisions, and scopes Carry out operations on data Master data containers, arrays, and collections Handle exceptions and access external libraries Who This Book Is For Very little programming experience is required: no prior knowledge of Kotlin needed.

Download or read book Kotlin Programming written by David Greenhalgh and published by Pearson Technology Group. This book was released on 2021-10-05 with total page 704 pages. Available in PDF, EPUB and Kindle. Book excerpt: Kotlin is a statically typed programming language designed to interoperate with Java and fully supported by Google on the Android operating system. It is also a multiplatform language that can be used to write code that can be shared across platforms including macOS, iOS, Windows, and JavaScript. Based on Big Nerd Ranch’s popular Kotlin Essentials course, this guide shows you how to work effectively with Kotlin through hands-on examples and clear explanations of key Kotlin concepts and foundational APIs. Written for Kotlin 1.5, this book will also introduce you to JetBrains’ IntelliJ IDEA development environment. Whether you are an experienced developer or are learning your first programming language – and whether you are interested in Kotlin for Android, server-side, or multiplatform projects – the authors will guide you from first principles to advanced Kotlin usage. By the end of this book, you will be empowered to create reliable, concise applications in Kotlin.

Download or read book Programming Kotlin written by Stephen Samuel and published by Packt Publishing Ltd. This book was released on 2017-01-18 with total page 413 pages. Available in PDF, EPUB and Kindle. Book excerpt: Familiarize yourself with all of Kotlin's features with this in-depth guide About This Book Get a thorough introduction to Kotlin Learn to use Java code alongside Kotlin without any hiccups Get a complete overview of null safety, Generics, and many more interesting features Who This Book Is For The book is for existing Java developers who want to learn more about an alternative JVM language. If you want to see what Kotlin has to offer, this book is ideal for you. What You Will Learn Use new features to write structured and readable object-oriented code Find out how to use lambdas and higher order functions to write clean, reusable, and simple code Write unit tests and integrate Kotlin tests with Java code in a transitioning code base Write real-world production code in Kotlin in the style of microservices Leverage Kotlin's extensions to the Java collections library Use destructuring expressions and find out how to write your own Write code that avoids null pointer errors and see how Java-nullable code can integrate with features in a Kotlin codebase Discover how to write functions in Kotlin, see the new features available, and extend existing libraries Learn to write an algebraic data types and figure out when they should be used In Detail Kotlin has been making waves ever since it was open sourced by JetBrains in 2011; it has been praised by developers across the world and is already being adopted by companies. This book provides a detailed introduction to Kotlin that shows you all its features and will enable you to write Kotlin code to production. We start with the basics: get you familiar with running Kotlin code, setting up, tools, and instructions that you can use to write basic programs. Next, we cover object oriented code: functions, lambdas, and properties – all while using Kotlin's new features. Then, we move on to null safety aspects and type parameterization. We show you how to destructure expressions and even write your own. We also take you through important topics like testing, concurrency, microservices, and a whole lot more. By the end of this book you will be able to compose different services and build your own applications. Style and approach An easy to follow guide that covers the full set of features in Kotlin programming.

Download or read book Kotlin Programming By Example written by Iyanu Adelekan and published by Packt Publishing Ltd. This book was released on 2018-03-28 with total page 490 pages. Available in PDF, EPUB and Kindle. Book excerpt: Enhance your Kotlin programming skills by building 3 real-world applications Key Features Build three full-fledged, engaging applications from scratch and learn to deploy them Enhance your app development and programming activities with Kotlin’s powerful and intuitive tools and utilities. Experience the gentle learning curve, expressiveness, and intuitiveness of Kotlin, as you develop your own applications Book Description Kotlin greatly reduces the verbosity of source code. With Google having announced their support for Kotlin as a first-class language for writing Android apps, now's the time learn how to create apps from scratch with Kotlin Kotlin Programming By Example takes you through the building blocks of Kotlin, such as functions and classes. You’ll explore various features of Kotlin by building three applications of varying complexity. For a quick start to Android development, we look at building a classic game, Tetris, and elaborate on object-oriented programming in Kotlin. Our next application will be a messenger app, a level up in terms of complexity. Before moving onto the third app, we take a look at data persistent methods, helping us learn about the storage and retrieval of useful applications. Our final app is a place reviewer: a web application that will make use of the Google Maps API and Place Picker. By the end of this book, you will have gained experience of of creating and deploying Android applications using Kotlin. What you will learn Learn the building blocks of the Kotlin programming language Develop powerful RESTful microservices for Android applications Create reactive Android applications efficiently Implement an MVC architecture pattern and dependency management using Kotlin Centralize, transform, and stash data with Logstash Secure applications using Spring Security Deploy Kotlin microservices to AWS and Android applications to the Play Store Who this book is for This book is for those who are new to Kotlin or are familiar with the basics, having dabbled with Java until now. Basic programming knowledge is mandatory.

Download or read book Effective Kotlin written by Marcin Moskała and published by Kt. Academy. This book was released on with total page 439 pages. Available in PDF, EPUB and Kindle. Book excerpt: Kotlin is a powerful and pragmatic language, but it's not enough to know about its features. We also need to know when they should be used and in what way. This book is a guide for Kotlin developers on how to become excellent Kotlin developers. It presents and explains in-depth the best practices for Kotlin development. Each item is presented as a clear rule of thumb, supported by detailed explanations and practical examples.

Download or read book Head First Kotlin written by Dawn Griffiths and published by O'Reilly Media. This book was released on 2019-02-13 with total page 483 pages. Available in PDF, EPUB and Kindle. Book excerpt: What will you learn from this book? Head First Kotlin is a complete introduction to coding in Kotlin. This hands-on book helps you learn the Kotlin language with a unique method that goes beyond syntax and how-to manuals and teaches you how to think like a great Kotlin developer. You’ll learn everything from language fundamentals to collections, generics, lambdas, and higher-order functions. Along the way, you’ll get to play with both object-oriented and functional programming. If you want to really understand Kotlin, this is the book for you. Why does this book look so different? Based on the latest research in cognitive science and learning theory, Head First Kotlin uses a visually rich format to engage your mind rather than a text-heavy approach that puts you to sleep. Why waste your time struggling with new concepts? This multisensory learning experience is designed for the way your brain really works.

Download or read book Learn Kotlin Programming written by Stephen Samuel and published by Packt Publishing Ltd. This book was released on 2019-05-29 with total page 497 pages. Available in PDF, EPUB and Kindle. Book excerpt: Delve into the world of Kotlin and learn to build powerful Android and web applications Key FeaturesLearn the fundamentals of Kotlin to write high-quality codeTest and debug your applications with the different unit testing frameworks in KotlinExplore Kotlin's interesting features such as null safety, reflection, and annotationsBook Description Kotlin is a general-purpose programming language used for developing cross-platform applications. Complete with a comprehensive introduction and projects covering the full set of Kotlin programming features, this book will take you through the fundamentals of Kotlin and get you up to speed in no time. Learn Kotlin Programming covers the installation, tools, and how to write basic programs in Kotlin. You'll learn how to implement object-oriented programming in Kotlin and easily reuse your program or parts of it. The book explains DSL construction, serialization, null safety aspects, and type parameterization to help you build robust apps. You'll learn how to destructure expressions and write your own. You'll then get to grips with building scalable apps by exploring advanced topics such as testing, concurrency, microservices, coroutines, and Kotlin DSL builders. Furthermore, you'll be introduced to the kotlinx.serialization framework, which is used to persist objects in JSON, Protobuf, and other formats. By the end of this book, you'll be well versed with all the new features in Kotlin and will be able to build robust applications skillfully. What you will learnExplore the latest Kotlin features in order to write structured and readable object-oriented codeGet to grips with using lambdas and higher-order functionsWrite unit tests and integrate Kotlin with Java codeCreate real-world apps in Kotlin in the microservices styleUse Kotlin extensions with the Java collections libraryUncover destructuring expressions and find out how to write your ownUnderstand how Java-nullable code can be integrated with Kotlin featuresWho this book is for If you’re a beginner or intermediate programmer who wants to learn Kotlin to build applications, this book is for you. You’ll also find this book useful if you’re a Java developer interested in switching to Kotlin.

Download or read book Mastering Kotlin written by Cybellium Ltd and published by Cybellium Ltd. This book was released on 2023-09-26 with total page 205 pages. Available in PDF, EPUB and Kindle. Book excerpt: Crafting the Future of Android and Beyond Embark on an enlightening exploration of Kotlin—the modern, concise, and expressive language that's redefining Android development and expanding its influence across various platforms. Whether you're just beginning your programming saga or are a veteran developer looking to update your toolkit, "Mastering Kotlin" offers the guidance and insights you need. Dive in and uncover: · Kotlin Foundations: Traverse the essentials of Kotlin, from its basic syntax to its functional and object-oriented programming paradigms. · Elevated Code: Grasp the nuances of idiomatic Kotlin, ensuring your code is both powerful and elegant. · Expert Techniques: Delve into advanced topics like coroutines, DSL creation, and multiplatform development, empowering you to harness Kotlin's full potential. · Practical Endeavors: Engage with hands-on projects that provide real-world context, ensuring your skills are battle-tested and industry-ready. · Interoperability Insights: Seamlessly integrate Kotlin with existing Java codebases and understand the harmony between these two juggernauts of the JVM. "Mastering Kotlin" is more than a guide—it's a compass, guiding you through the ever-evolving landscape of modern development with clarity and precision. Step into the future of development with Kotlin at your fingertips.

Download or read book Android Development with Kotlin written by Marcin Moskala and published by Packt Publishing Ltd. This book was released on 2017-08-30 with total page 435 pages. Available in PDF, EPUB and Kindle. Book excerpt: Learn how to make Android development much faster using a variety of Kotlin features, from basics to advanced, to write better quality code. About This Book Leverage specific features of Kotlin to ease Android application development Write code based on both object oriented and functional programming to build robust applications Filled with various practical examples so you can easily apply your knowledge to real world scenarios Identify the improved way of dealing with common Java patterns Who This Book Is For This book is for developers who have a basic understanding of Java language and have 6-12 months of experience with Android development and developers who feel comfortable with OOP concepts. What You Will Learn Run a Kotlin application and understand the integration with Android Studio Incorporate Kotlin into new/existing Android Java based project Learn about Kotlin type system to deal with null safety and immutability Define various types of classes and deal with properties Define collections and transform them in functional way Define extensions, new behaviours to existing libraries and Android framework classes Use generic type variance modifiers to define subtyping relationship between generic types Build a sample application In Detail Nowadays, improved application development does not just mean building better performing applications. It has become crucial to find improved ways of writing code. Kotlin is a language that helps developers build amazing Android applications easily and effectively. This book discusses Kotlin features in context of Android development. It demonstrates how common examples that are typical for Android development, can be simplified using Kotlin. It also shows all the benefits, improvements and new possibilities provided by this language. The book is divided in three modules that show the power of Kotlin and teach you how to use it properly. Each module present features in different levels of advancement. The first module covers Kotlin basics. This module will lay a firm foundation for the rest of the chapters so you are able to read and understand most of the Kotlin code. The next module dives deeper into the building blocks of Kotlin, such as functions, classes, and function types. You will learn how Kotlin brings many improvements to the table by improving common Java concepts and decreasing code verbosity. The last module presents features that are not present in Java. You will learn how certain tasks can be achieved in simpler ways thanks to Kotlin. Through the book, you will learn how to use Kotlin for Android development. You will get to know and understand most important Kotlin features, and how they can be used. You will be ready to start your own adventure with Android development with Kotlin.

Download or read book Android Programming with Kotlin for Beginners written by John Horton and published by Packt Publishing Ltd. This book was released on 2019-04-30 with total page 699 pages. Available in PDF, EPUB and Kindle. Book excerpt: Build smart looking Kotlin apps with UI and functionality for the Android platform Key FeaturesStart your Android programming career, or just have fun publishing apps on Google Play marketplaceThe first-principle introduction to Kotlin through Android, to start building easy-to-use appsLearn by example and build four real-world apps and dozens of mini-appsBook Description Android is the most popular mobile operating system in the world and Kotlin has been declared by Google as a first-class programming language to build Android apps. With the imminent arrival of the most anticipated Android update, Android 10 (Q), this book gets you started building apps compatible with the latest version of Android. It adopts a project-style approach, where we focus on teaching the fundamentals of Android app development and the essentials of Kotlin by building three real-world apps and more than a dozen mini-apps. The book begins by giving you a strong grasp of how Kotlin and Android work together before gradually moving onto exploring the various Android APIs for building stunning apps for Android with ease. You will learn to make your apps more presentable using different layouts. You will dive deep into Kotlin programming concepts such as variables, functions, data structures, Object-Oriented code, and how to connect your Kotlin code to the UI. You will learn to add multilingual text so that your app is accessible to millions of more potential users. You will learn how animation, graphics, and sound effects work and are implemented in your Android app. By the end of the book, you will have sound knowledge about significant Kotlin programming concepts and start building your own fully featured Android apps. What you will learnLearn how Kotlin and Android work togetherBuild a graphical drawing app using Object-Oriented Programming (OOP) principlesBuild beautiful, practical layouts using ScrollView, RecyclerView, NavigationView, ViewPager and CardViewWrite Kotlin code to manage an apps' data using different strategies including JSON and the built-in Android SQLite databaseAdd user interaction, data captures, sound, and animation to your appsImplement dialog boxes to capture input from the userBuild a simple database app that sorts and stores the user's dataWho this book is for This book is for people who are new to Kotlin, Android and want to develop Android apps.It also acts as a refresher for those who have some experience in programming with Android and Kotlin.

Download or read book Android Studio 3 0 Development Essentials Android 8 Edition written by Neil Smyth and published by Payload Media, Inc.. This book was released on 2017-11-25 with total page 757 pages. Available in PDF, EPUB and Kindle. Book excerpt: Fully updated for Android Studio 3.0 and Android 8, the goal of this book is to teach the skills necessary to develop Android based applications using the Android Studio Integrated Development Environment (IDE), the Android 8 Software Development Kit (SDK) and the Java programming language. Beginning with the basics, this book provides an outline of the steps necessary to set up an Android development and testing environment. An overview of Android Studio is included covering areas such as tool windows, the code editor and the Layout Editor tool. An introduction to the architecture of Android is followed by an in-depth look at the design of Android applications and user interfaces using the Android Studio environment. More advanced topics such as database management, content providers and intents are also covered, as are touch screen handling, gesture recognition, camera access and the playback and recording of both video and audio. This edition of the book also covers printing, transitions and cloud-based file storage. The concepts of material design are also covered in detail, including the use of floating action buttons, Snackbars, tabbed interfaces, card views, navigation drawers and collapsing toolbars. In addition to covering general Android development techniques, the book also includes Google Play specific topics such as implementing maps using the Google Maps Android API, and submitting apps to the Google Play Developer Console. Other key features of Android Studio 3 and Android 8 are also covered in detail including the Layout Editor, the ConstraintLayout and ConstraintSet classes, constraint chains and barriers, direct reply notifications and multi-window support. Chapters also cover advanced features of Android Studio such as App Links, Instant Apps, the Android Studio Profiler and Gradle build configuration. Assuming you already have some Java programming experience, are ready to download Android Studio and the Android SDK, have access to a Windows, Mac or Linux system and ideas for some apps to develop, you are ready to get started.

Download or read book Learn Android Studio 3 with Kotlin written by Ted Hagos and published by Apress. This book was released on 2018-11-12 with total page 480 pages. Available in PDF, EPUB and Kindle. Book excerpt: Build Android apps using the popular and efficient Android Studio 3 suite of tools, an integrated development environment (IDE) with which Android developers can now use the Kotlin programming language. With this book, you’ll learn the latest and most productive tools in the Android tools ecosystem, ensuring quick Android app development and minimal effort on your part. Along the way, you’ll use Android Studio to develop apps tier by tier through practical examples. These examples cover core Android topics such as Activities, Intents, BroadcastReceivers, Services and AsyncTask. Then, you’ll learn how to publish your apps and sell them online and in the Google Play store. What You’ll LearnUse Android Studio 3 to quickly and confidently build your first Android apps Build an Android user interface using activities and layouts, event handling, images, menus and the action bar Incorporate new elements including fragments Learn how data is persisted Use Kotlin to build apps Who This Book Is For Those who may be new to Android Studio 3 or Android Studio in general. You may or may not be new to Android development in general. Some prior experience with Java is also recommended.

Download or read book Mastering Android Development with Kotlin written by Milos Vasic and published by Packt Publishing Ltd. This book was released on 2017-11-08 with total page 366 pages. Available in PDF, EPUB and Kindle. Book excerpt: Master Android development using a variety of Kotlin features About This Book Leverage specific features of Kotlin to ease Android application development An illustrative guide that will help you write code based Kotlin language to build robust Android applications Filled with various practical examples build amazing Android project using Kotlin so you can easily apply your knowledge to real world scenarios Who This Book Is For The book is for developers who want to build amazing Android applications in an easy and effective way. Basic knowledge of Kotlin is assumed, but you do not need any familiarity with Android development. What You Will Learn Understand the basics of Android development with Kotlin Get to know the key concepts in Android development See how to create modern mobile applications for the Android platform Adjust your application's look and feel Know how to persist and share application database Work with Services and other concurrency mechanisms Write effective tests Migrate an existing Java-based project to Kotlin In Detail Kotlin is a programming language intended to be a better Java, and it's designed to be usable and readable across large teams with different levels of knowledge. As a language, it helps developers build amazing Android applications in an easy and effective way. This book begins by giving you a strong grasp of Kotlin's features in the context of Android development and its APIs. Moving on, you'll take steps toward building stunning applications for Android. The book will show you how to set up the environment, and the difficulty level will grow steadily with the applications covered in the upcoming chapters. Later on, the book will introduce you to the Android Studio IDE, which plays an integral role in Android development. We'll use Kotlin's basic programming concepts such as functions, lambdas, properties, object-oriented code, safety aspects, type parameterization, testing, and concurrency, which will guide you through writing Kotlin code into production. We'll also show you how to integrate Kotlin into any existing Android project. Style and approach In this book, you'll master Android development using Kotlin through real application examples. We'll introduce you to basic Android concepts and offer guidance from the first steps to the final project. In each chapter, we'll develop one important application functionality as a development milestone. As we progress, you'll become more experienced in Android and our application will progress toward a real-world product. Finally, when we complete the application's development, we'll write proper tests to ensure it's production ready.

Download or read book Learn to Program with Kotlin written by Tim Lavers and published by Apress. This book was released on 2021-06-12 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Teach yourself programming starting with the basics and progressing to a series of exciting projects using Kotlin, one of today's hottest programming languages. This book starts with the absolute basics and then introduces just enough syntax to get into some fascinating projects. These include text processing: a statistical analysis of Jane Austen's novels, solving anagrams, and working with palindromes; image processing: cropping and resizing images, and pixel transformation; and computer vision: finding digits, parsing images, and reading speed signs. The projects are developed in tiny steps and complete solutions are provided. Some of these projects include core data science concepts, giving you skills in one of the most important areas of modern programming. Along the way you’ll cover functional programming, object-oriented programming (OOP), refactoring, and writing unit tests. After reading Learn to Program with Kotlin, you'll come away with practical insights and code to get you started right away with programming using Kotlin for your own projects. What You Will Learn Gain the basics of Kotlin using the IntelliJ Java IDE Implement OOP with Kotlin along with unit testing and code refactoring using a series of text-related projects Harness functional programming with Kotlin by building an image-processing library Write software to locate and read speed signs in photos Who Is This Book For Anyone who wants to learn how to program or code from scratch. Also great for experienced programmers who want to know more about Kotlin.