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Kotlin The good Moyinoluwa Adeyemi

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Kotlin The good, the bad and the ugly Segun Famisa Moyinoluwa Adeyemi

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Intro to Kotlin - History Statically typed programming language, and runs on the JVM.

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

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Intro to Kotlin - 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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Intro to Kotlin - 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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Interesting Features of Kotlin

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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 // compiler error var name: String name = null A non-nullable object can’t be null Protects against NullPointerException the $1,000,000,000 mistake

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

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

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Null Safety - Accessing properties in a nullable object // use ?. to make safe call var name: String? = null ... 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. 2. Making safe calls using “?.”

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

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Null Safety - Accessing properties in a nullable object // use !! assertion 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” 4. Making use of the “!!” assertion operator

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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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Smart inference // you don’t need to explicitly put a type val name = "Segun" // string val age = 24 // int val grade = 'A' // char val hobbies = listOf("karate", "eating") // list of strings Kotlin can smartly infer the type of your variable from the data it contains

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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 = "Moyin" name = name.toUpperCase() // works fine var name = "Moyin" 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("karate", "basketball") changeableHobbies.add("soccer") // you can add

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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) Immutability in Java vs Kotlin

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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() } Method parameters use the “name:Type” notation Return types are specified after the method definition. A function is declared using the “fun” keyword

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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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Conciseness

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

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

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

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

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

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

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Classes

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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) Classes in Java vs Data Classes in Kotlin

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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(var name: String) { val nameLength: Int get() = name.length }

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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(var name: String) { val nameLength get() = name.length }

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Getting started

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Kotlin Koans ● Koans online

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Kotlin Koans ● Koans online ● Offline Kotlin Educational Plugin

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Kotlin Koans ● Koans online ● Offline Kotlin Educational Plugin ● Clone the project on Github

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Kotlin Koans ● Koans online ● Offline Kotlin Educational Plugin ● Clone the project on Github IDE support Kotlin Koans + plugin

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Kotlin Koans ● Koans online ● Offline Kotlin Educational Plugin ● Clone the project on Github IDE support = built-in support + plugin

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Kotlin Koans ● Koans online ● Offline Kotlin Educational Plugin ● Clone the project on Github IDE support = built-in support = built-in support + plugin

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Kotlin Koans ● Koans online ● Offline Kotlin Educational Plugin ● Clone the project on Github IDE support Community Kotlin Weekly http://www.kotlinweekly.net/ = built-in support = built-in support + plugin

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Kotlin Koans ● Koans online ● Offline Kotlin Educational Plugin ● Clone the project on Github IDE support Community Kotlin Weekly http://www.kotlinweekly.net/ Kotlin Conf kotlinconf.com + = built-in support plugin = built-in support

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Thank you! @segunfamisa segunfamisa.com @moyheen medium.com/@moyinoluwa