Kotlin Kotlin is a free and open-source general-purpose programming language that is mostly used to create Android apps. Kotlin was developed by JetBrains initially and later picked up by Google as the language of choice for its Android platform. Over the past few years, Kotlin has become one of the most popular alternatives to Java language and is used by more than 80 percent of Android app developers. Kotlin is a statically typed, advanced programming language that compiles Kotlin code into Java byte-code and runs on a Java Virtual Machine (JVM). It can also be compiled to native executables and JavaScript source code. It is an object-oriented programming language that includes data types, operators, I/O comments, control statements, functions, classes, object expressions, and constructors, among other features. It is not a standalone programming language; rather, is an innovative manner of coding that runs on Java. Kotlin is a versatile language with some interesting and cool features like compat- ibility, low runtime, and efficient coding characteristics. The features that help dis- tinguish Kotlin from other languages are its reliability, tool support, and interoper- ability. It is a simplified version of Java that is much easier to deal with. Why Should You Learn Kotlin? The popularity of Kotlin is growing, and it will continue to do so in the coming years. Kotlin has always been, and will continue to be, a cutting-edge program- ming language that best meets the needs of real professionals. Many emerging fields, including mobile, online gaming, server-side, cloud development, data science, and education, are progressively using Kotlin. All of this indicates that there is already a high demand for Kotlin developers, and that demand will continue to grow in the future. Furthermore, if you are looking to build native Android apps, Kotlin is the language that you should be using. Kotlin The Ultimate Guide Edited by Sufyan bin Uzayr First edition published 2023 by CRC Press 6000 Broken Sound Parkway NW, Suite 300, Boca Raton, FL 33487-2742 and by CRC Press 4 Park Square, Milton Park, Abingdon, Oxon, OX14 4RN CRC Press is an imprint of Taylor & Francis Group, LLC © 2023 Sufyan bin Uzayr Reasonable efforts have been made to publish reliable data and information, but the author and publisher cannot assume responsibility for the validity of all materials or the consequences of their use. The authors and publishers have attempted to trace the copyright holders of all material reproduced in this publication and apologize to copyright holders if permission to publish in this form has not been obtained. If any copyright material has not been acknowledged please write and let us know so we may rectify in any future reprint. 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Description: First edition. | Boca Raton : CRC Press, 2023. | Includes bibliographical references and index. Identifiers: LCCN 2022025675 (print) | LCCN 2022025676 (ebook) | ISBN 9781032311708 (hardback) | ISBN 9781032311692 (paperback) | ISBN 9781003308447 (ebook) Subjects: LCSH: Android (Electronic resource) | Kotlin (Computer program language) | Application software--Development. | Mobile apps--Development. | Java (Computer program language) Classification: LCC QA76.73.K68 B56 2023 (print) | LCC QA76.73.K68 (ebook) | DDC 005.1/14--dc23/eng/20220917 LC record available at https://lccn.loc.gov/2022025675 LC ebook record available at https://lccn.loc.gov/2022025676 ISBN: 9781032311708 (hbk) ISBN: 9781032311692 (pbk) ISBN: 9781003308447 (ebk) DOI: 10.1201/9781003308447 Typeset in Minion by KnowledgeWorks Global Ltd. Contents Acknowledgments, xxi About the Author, xxiii Chapter 1 ◾ C rash Course in Kotlin 1 KOTLIN PROGRAMMING LANGUAGE HAS A RICH HISTORY 2 FEATURES OF THE KOTLIN PROGRAMMING LANGUAGE 2 KOTLIN PROGRAMMING LANGUAGE APPLICATIONS 4 WHY SHOULD WE STUDY THE KOTLIN PROGRAMMING LANGUAGE? WHAT ARE THE BENEFITS OF LEARNING THE KOTLIN PROGRAMMING LANGUAGE? 4 DISADVANTAGES OF KOTLIN 5 WHAT IS THE PURPOSE OF KOTLIN? 5 Android Development 5 Back-End Web Development 6 Full-Stack Web Development 6 Data Science 6 Mobile Development for Several Platforms 7 KOTLIN’S ARCHITECTURE 7 KOTLIN FRAMEWORKS FOR SERVER-SIDE DEVELOPMENT 8 KOTLIN ENVIRONMENT FOR COMMAND LINE SETUP 9 Intellij IDEA IS USED TO BUILD UP A KOTLIN ENVIRONMENT 9 THE FIRST PROGRAM IS WRITTEN IN KOTLIN 11 KOTLIN DATA TYPES 12 Number Data Types in Kotlin 12 Character Data Type in Kotlin 13 v vi ◾ Contents String Data Type in Kotlin 14 Boolean Data Type in Kotlin 14 Array Data Type in Kotlin 15 DATA TYPE CONVERSION IN KOTLIN 15 OPERATORS IN KOTLIN 16 Arithmetic Operators in Kotlin 16 Relational Operators in Kotlin 17 Assignment Operators in Kotlin 17 Unary Operators in Kotlin 18 Logical Operators in Kotlin 19 Bitwise Operations in Kotlin 19 BOOLEANS IN KOTLIN 20 Create Boolean Variables 20 Boolean Operators in Kotlin 21 Boolean Expression in Kotlin 21 and() and or() Functions in Kotlin 22 Boolean to String 22 STRINGS IN KOTLIN 22 String Templates in Kotlin 23 String Object in Kotlin 23 String Indexes in Kotlin 23 String Length in Kotlin 24 String Kotlin Last Index 24 String Case Changing 24 String Concatenation in Kotlin 25 Trim Characters from the String 25 Quotes Inside a String 26 Finding a String Inside a String 26 Comparing Two Strings 26 getOrNull() Function in Kotlin 26 toString() Function in Kotlin 27 Contents ◾ vii ARRAYS IN KOTLIN 27 Creating Arrays 27 Arrays of the Primitive Type 28 Elements of an Array Can Be Get and Set 28 Array Length in Kotlin 28 Loop through an Array 29 Check if an Element Exists 29 Distinct Values from the Array 29 Dropping Elements from the Array 30 Checking an Empty Array 30 RANGES IN KOTLIN 30 Creating Ranges Using the rangeTo() Function 31 Creating the Ranges Using the .. Operator 31 Creating the Ranges Using downTo() Operator 31 step() Function in Kotlin 32 Range of Characters in Kotlin 32 reversed() Function in Kotlin 32 until() Function in Kotlin 32 The last, first, and step Elements 33 Filtering Ranges 33 Distinct Values in Range 33 Range Utility Functions 34 FUNCTIONS IN KOTLIN 34 Built-in Functions in Kotlin 34 User-Defined Functions 34 Function Parameters 35 Return Values 35 Unit-Returning Functions 36 Recursive Function in Kotlin 36 Tail Recursion in Kotlin 37 Higher-Order Functions 38 viii ◾ Contents Lambda Function in Kotlin 38 Inline Function in Kotlin 38 If-else EXPRESSION IN KOTLIN 39 if Statement 39 if-else Statement 40 if-else Expression in Kotlin as the Ternary Operator 42 if-else-if Ladder Expression 42 nested if Expression 44 while loop IN KOTLIN 45 do-while loop IN KOTLIN 47 Method of do-while loop 47 for loop IN KOTLIN 48 Iterate across the Range Using a for loop 49 Using a for loop, Iterate over the Array 50 Iterate through a String Using the for loop 51 Iterate over the Collection Using the for loop 52 KOTLIN when expression 52 when to Use as a Statement with else 53 Using when as a Statement in the Absence of an else Branch 53 when Used as an Expression 53 In Kotlin, Different Ways to Use a when Block 54 UNLABELED BREAKS IN KOTLIN 57 In a while loop, Use of an Unlabeled Break 57 In a do-while loop, Use of an Unlabeled Break 58 Use of an Unlabeled Break in a for loop 59 LABELED BREAKS IN KOTLIN 60 In a while loop, Using a Labeled Break 60 In a do-while loop, Using a Labeled Break 61 Using a Labeled Break in a for loop 62 KOTLIN UNLABELED CONTINUE 63 Use of Unlabeled Continues in the while loop 63 Contents ◾ ix In a do-while loop, Use an Unlabeled Continue 64 Use of Unlabeled Continues in a for loop 64 KOTLIN LABELED CONTINUES 65 Use of Labeled Continues in a while loop 65 Use of Labeled Continues in a do-while loop 66 Use of Labeled Continues in a for loop 67 EXCEPTIONAL HANDLING 68 Exceptions in Kotlin 68 Exception Handling in Kotlin 69 Avoiding NullPointerException 70 What If We Fail to Deal with Exceptions? 70 How to Throw an Exception 70 KOTLIN try-catch block 71 The try-catch block as an Expression in Kotlin 72 The final block in Kotlin 72 Kotlin throw keyword 74 NESTED try block AND MULTIPLE catch block 74 Nested try block 74 Multiple catch block 75 NULL SAFETY 77 Nullable and Non-Nullable Sorts in Kotlin 77 Checking for the null in Conditions 78 Safe Call operator(?.) 79 Elvis Operator(?:) 80 Not null assertion: !! Operator 80 TYPE CHECKING AND SMART CASTING 81 Type Checking 81 Smart Casting 82 Use of !is Operator 83 EXPLICIT TYPE CASTING 83 Unsafe Cast Operator: as 84 Safe Cast Operator: as? 85