Kotlin 101

The Basics of Kotlin Programming Language

Transcript

1. otlin 101 - the basics @HSM59 +HussainMukadam
2. What’s Kotlin?
3. Statically typed programming language for modern multiplatform applications 100% interoperable with Java ™ and Android ™
5. Basic Types and Syntax • Classes and fields • Primary constructor • Function and overrides • Mutability & Nullability • Equality • Any versus object • Imports and Data Classes
6. Basic Syntax fun main(args: Array<String>) { println("Hello Kotlin!") } public static void main(String[] args) { System.out.println(“Good bye Java!”); }
7. Basic Syntax val - Immutable (For values that don’t change) var - Mutable (For variables that change) //Variable type is inferred from the context val name = "John" name = 2 //Error, because name type is String //Explicit type var list : List<String> = ArrayList()
8. class Person open class Person private class Person class Person(val name: String, val age: Int) class Person(var name: String, var age: Int) class Person private constructor(name: String, age: Int) annotation class Inject class Person @Inject constructor(val name: String, val age: Int) Class Declarations
9. class Person(val name: String, val age: Int) fun main(args: Array<String>) { val person = Person("John Doe", 30) //Reassigning person.age = 40 //Error } //Creates a setter class Person(val name: String, var age: Int) Fields
10. class Person(val name: String, var age: Int) fun main(args: Array<String>) { val person = Person("John Doe", 30) //Assigning null person.age = null //Error } //Makes it a Nullable type class Person(val name: String, var age: Int?) Nullability
11. //Do this, when you’re sure enough it won’t be null val nextAge = person.age!! + 1 //Use Elvis Operator val nextAge = (person.age ?: 0) + 1 //Error val nextAge = person.age + 1 //We can use safe call operator to safely call methods on potentially nullable variables savedInstanceState?.doSomething()
12. class Person(val name: String, var age: Int){ override fun toString(): String { return "$name is $age years old" } override fun equals(other: Any?): Boolean { return (other is Person && other.name == name) } } Equality and String interpolation
13. Any versus Object
14. Aliases and Importing functions import com.example.MyClass import com.example.* //Import with an Alias import com.example.MyLongClassName as MLCN //Import Package level function import com.example.hello
15. Default Imports • kotlin.* • kotlin.annotation.* • kotlin.collections.* • kotlin.comparisons.* • kotlin.io.* • kotlin.ranges.* • kotlin.sequences.* • kotlin.text.* • java.lang • kotlin.jvm.*
16. package com.example.pkg1 class Greeter{ fun hello() = "Hello from Package 1" } package com.example.pkg2 class Greeter{ fun hello() = "Hello from Package 2" } Expression body
17. package com.example.pkg3 import com.example.pkg1.Greeter as G1 import com.example.pkg2.Greeter as G2 fun main(args: Array<String>) { println(G1().hello()) println(G2().hello()) } Aliases
18. Data Classes • data class Person(val name: String, val age: Int) • Along with this you get - • equals/hashcode • toString() like Person(name=John Doe, age=42) • Destructuring declarations - componentN() • Copy with modified attributes - copy()
19. data class Person(val name: String, val age: Int) fun main(args: Array<String>) { val person = Person("John Doe", 42) val (name, age) = person } Destructuring Declaration Copy() val person2 = person.copy("Johnny Depp", 54) println(person2)
20. Next in the series - • Singleton (object keyword) • Enabling Inheritance • Object Expressions • Companion Objects • Efficient Type Checking and Smart Casts • Extension functions, Higher order functions, etc
21. • Kotlin Lang on Slack • Talking Kotlin Podcast by Hadi Hariri • Learning Kotlin Series on Fragmented Podcast • From Java to Kotlin • Antonio Leiva’s blog • Android development with Kotlin - Jake Wharton • Kotlinize your Android Development - Akshay Chordiya References