Kotlin: what you need to know

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Umar Saidu Auna, Flexisaf Edusoft @umarauna otlin: what you need to know October 27, 2018 Yola

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About me Yola - Android Developer since 2014. - Started GDG Minna 2014. - Graduate of BUK CS Student. - Founded Sysbit Nigeria. - Intern @ Flexisaf Edusoft. - Volunteer @ Nigerian Red Cross Society. - and I love meeting new people.

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otlin history

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History Statically typed programming language, and runs on the JVM.

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History Statically typed programming language, and runs on the JVM. Kotlin was developed by JetBrains (Makers of IntelliJ)

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History Statically typed programming language, and runs on the JVM. Kotlin was developed by JetBrains (Makers of IntelliJ) First commit dates back to 2010, but was first publicly seen around 2011.

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History - Why did Google make it official? Awesome features - nullable types, concise, data classes, etc. Great community support There was an overwhelming request for Kotlin official support on Android

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otlin What?

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What is Kotlin Kotlin, as described before, is a JVM based language developed by JetBrains, a company known for the creation of IntelliJ IDEA, a powerful IDE for Java development. In Kotlin everything is an Object. Kotlin is very intuitive and easy to learn for Java developers (give it 10 days trials and you wont regret).

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otlin interesting features

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“In Kotlin, everything is an object (reference type), we don’t find primitives types as the ones we can use in Java……...”

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Kotlin sample code….. fun main(args: Array){ //your code goes here }

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As of Kotlin 1.3 no more (args: Array) fun main(){ //your code goes here }

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Null Safety - nullable types and non-nullable types Protects against NullPointerException the $1,000,000,000 mistake

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Null Safety - nullable types and non-nullable types Protects against NullPointerException the $1,000,000,000 mistake // compiler error var name: String A non-nullable object can’t be null name = null // compiler error Specify a nullable object by using “?” var name: String? val length = name.length Kotlin ensures that you don’t mistakenly operate on nullable objects

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Null Safety - Accessing properties in a nullable object 1. Checking for null types // handle non-null case and null case var name: String? = null val length = if (name != null) name.length else 0

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Null Safety - Accessing properties in a nullable object 2. Making safe calls using “?.” //use ?. to make safe call var name: String? ... val length = name?.length Use ?. to safely access a property/method on a nullable object If name happens to be null, the value of length is 0 (inferred integer). length would be null if it were of another type.

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Null Safety - Accessing properties in a nullable object 3. Making use of the “?:” elvis operator //use elvis operator var name: String? val length = name?.length ?: 0 This reads as “if name is not null, use name.length else use 0

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Null Safety - Accessing properties in a nullable object 4. Making use of the “!!” assertion operator //use elvis operator var name: String? = null val length = name!!.length This reads as “if name is not null, use name.length else throw a null pointer exception”

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Null Safety - NPE free! You can only have the NullPointerException in Kotlin if: 1. You explicitly throw a NPE 2. You make use of the !! operator 3. An external Java code causes the NPE.

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String Interpolation in Kotlin fun hello(name: String) { println("Hello, $name") }

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String Interpolation in Java + Kotlin void hello(String name) { System.out.println("Hello, " + name); }

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Immutability Kotlin helps developers to be intentional about immutability. Immutability simply means that things you create can’t be changed. We need immutability because it: ● helps us with thread safety - no synchronization issues ● is good for value objects - objects that simply hold value, POJOs etc. ● helps debugging threaded applications without losing your hair

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Immutability How does it work in Java? ● Immutability in Java? final classes private fields no setters ● Immutability in Kotlin? Guess?

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Immutability How does Kotlin help? var vs val // compiler error: val cannot be reassigned val name = "Umar" name = name.toUpperCase() // works fine var name = "Umar" name = name.toUpperCase()

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Immutability How does Kotlin help? Immutable and Mutable collections // immutable collection val unchangeableHobbies = listOf("coding", "eating") unchangeableHobbies.add() // add method doesn’t exist // mutable collection val changeableHobbies = mutableListOf("reading", "running") changeableHobbies.add("volleyball") // you can add

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Immutability In Java vs Kotlin public final class ImmutableClassJava { private final String name; private final int age; public ImmutableClassJava(String name, int age) { this.name = name; this.age = age; } // no setters public String getName() { return name; } public int getAge() { return age; } } class ImmutableClass(val name: String, val age: Int, val grade: Char, val hobbies: List) ● Class is final by default ● val implies that the parameters are final as well (values can’t be assigned)

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Functions // function sample fun sampleFunc() { // code goes here } A function is declared using the “fun” keyword

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Functions // function sample fun sampleFunc() { // code goes here } // function with param fun sampleFuncWithParam(param: String) { // code goes here } A function is declared using the “fun” keyword Method parameters use the “name:Type” notation

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Functions // function sample fun sampleFunc() { // code goes here } // function with param fun sampleFuncWithParam(param: String) { // code goes here } // func with param and return type fun capitalize(param: String): String { return param.toUpperCase() } A function is declared using the “fun” keyword Method parameters use the “name:Type” notation Return types are specified after the method definition.

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Functions - infix functions // infix function infix fun Int.times(x: Int): Int { return this * x }

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Functions - infix functions // infix function infix fun Int.times(x: Int): Int { return this * x } // usage fun useInfix() { val product = 2 times 5 println(product) }

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Functions - extension functions // extension function fun Int.square(): Int { return this * this }

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Functions - extension functions // extension function fun Int.square(): Int { return this * this } fun useExtension() { val square = 2.square() println(square) }

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Functions Others: ● Higher order functions ● Lambdas ● Inline functions etc.

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Iterators Java Kotlin

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When Expression

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otlin conciseness

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Conciseness in Kotlin public void doSomething() { // do something } fun doSomething(): Unit { // do same thing }

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Conciseness in Kotlin public void doSomething() { // do something } fun doSomething(): Unit { // do same thing }

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Conciseness in Kotlin public void doSomething() { // do something } fun doSomething() { // do same thing }

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Conciseness in Kotlin public String getName() { return name; } fun getName(): String { return name }

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Conciseness in Kotlin public String getName() { return name; } fun getName() { return name }

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Conciseness in Kotlin public String getName() { return name; } fun getName() = name

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otlin classes

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Classes in Java vs Data Classes in Kotlin public class Person { private String name; String getName () { return name; } void setName (String name) { this.name = name; } @Override public String toString () { return "Person{" + "name='" + name + '\'' + '}'; } } data class Person(val name: String)

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Classes in Java vs Regular Classes in Kotlin public class Person { private String name; String getName () { return name; } void setName (String name) { this.name = name; } public int getNameLength () { return name.length } } class Person(name: String) { var name: String get() = name set(name) { this.name = name } fun getNameLength(): int { return name.length } }

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otlin: getting started

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Important place to learn…….

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Important place to learn……. Tutorials Point - Kotlin

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Important place to learn……. Tutorials Point - Kotlin Kotlin for Android Developers – Antonio Leiva

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Important place to learn……. Tutorials Point - Kotlin Kotlin for Android Developers – Antonio Leiva Koans online – try.kotl.in/koans

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Important place to learn……. Tutorials Point - Kotlin Kotlin for Android Developers – Antonio Leiva Koans online – try.kotl.in/koans Kotlin Bootcamp for Programmers - Udacity

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Compilations

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IDE’s

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Build Tools

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Stay updated……. Kotlin Weekly http://www.kotlinweekly.net/ Kotlin Conf kotlinconf.com

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Summary • Interoperable with Java (100%) • Reduces Boilerplate code • Object-Oriented and procedural • Safety code • No Semicolon • Expands your skillset • Perfect Support with Android Studio & Gradle • Very easy to get started with Android Development

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otlin: libraries

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Reduces Boilerplates codes like: findViewById, Async, build interfaces with Kotlin code etc

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Kotlin Android Extension it includes a view binder. The plugin automatically creates a set of properties that give direct access to all the views in the XML.