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Diffstat (limited to 'kotlin.html.markdown')
| -rw-r--r-- | kotlin.html.markdown | 113 |
1 files changed, 94 insertions, 19 deletions
diff --git a/kotlin.html.markdown b/kotlin.html.markdown index d1f1aae6..12008074 100644 --- a/kotlin.html.markdown +++ b/kotlin.html.markdown @@ -20,7 +20,9 @@ package com.learnxinyminutes.kotlin /* The entry point to a Kotlin program is a function named "main". -The function is passed an array containing any command line arguments. +The function is passed an array containing any command-line arguments. +Since Kotlin 1.3 the "main" function can also be defined without +any parameters. */ fun main(args: Array<String>) { /* @@ -36,7 +38,7 @@ fun main(args: Array<String>) { so we don't have to explicitly specify it every time. We can explicitly declare the type of a variable like so: */ - val foo : Int = 7 + val foo: Int = 7 /* Strings can be represented in a similar way as in Java. @@ -65,7 +67,7 @@ fun helloWorld(val name : String) { A template expression starts with a dollar sign ($). */ val fooTemplateString = "$fooString has ${fooString.length} characters" - println(fooTemplateString) + println(fooTemplateString) // => My String Is Here! has 18 characters /* For a variable to hold null it must be explicitly specified as nullable. @@ -107,7 +109,7 @@ fun helloWorld(val name : String) { /* When a function consists of a single expression then the curly brackets can - be omitted. The body is specified after a = symbol. + be omitted. The body is specified after the = symbol. */ fun odd(x: Int): Boolean = x % 2 == 1 println(odd(6)) // => false @@ -175,12 +177,12 @@ fun helloWorld(val name : String) { // Objects can be destructured into multiple variables. val (a, b, c) = fooCopy println("$a $b $c") // => 1 100 4 - + // destructuring in "for" loop for ((a, b, c) in listOf(fooData)) { - println("$a $b $c") // => 1 100 4 + println("$a $b $c") // => 1 2 4 } - + val mapData = mapOf("a" to 1, "b" to 2) // Map.Entry is destructurable as well for ((key, value) in mapData) { @@ -189,13 +191,13 @@ fun helloWorld(val name : String) { // The "with" function is similar to the JavaScript "with" statement. data class MutableDataClassExample (var x: Int, var y: Int, var z: Int) - val fooMutableDate = MutableDataClassExample(7, 4, 9) - with (fooMutableDate) { + val fooMutableData = MutableDataClassExample(7, 4, 9) + with (fooMutableData) { x -= 2 y += 2 z-- } - println(fooMutableDate) // => MutableDataClassExample(x=5, y=6, z=8) + println(fooMutableData) // => MutableDataClassExample(x=5, y=6, z=8) /* We can create a list using the "listOf" function. @@ -304,7 +306,7 @@ fun helloWorld(val name : String) { println(result) /* - We can check if an object is a particular type by using the "is" operator. + We can check if an object is of a particular type by using the "is" operator. If an object passes a type check then it can be used as that type without explicitly casting it. */ @@ -344,15 +346,25 @@ fun helloWorld(val name : String) { return this.filter {it != c} } println("Hello, world!".remove('l')) // => Heo, word! - - println(EnumExample.A) // => A - println(ObjectExample.hello()) // => hello } // Enum classes are similar to Java enum types. enum class EnumExample { - A, B, C + A, B, C // Enum constants are separated with commas. } +fun printEnum() = println(EnumExample.A) // => A + +// Since each enum is an instance of the enum class, they can be initialized as: +enum class EnumExample(val value: Int) { + A(value = 1), + B(value = 2), + C(value = 3) +} +fun printProperty() = println(EnumExample.A.value) // => 1 + +// Every enum has properties to obtain its name and ordinal(position) in the enum class declaration: +fun printName() = println(EnumExample.A.name) // => A +fun printPosition() = println(EnumExample.A.ordinal) // => 0 /* The "object" keyword can be used to create singleton objects. @@ -363,17 +375,80 @@ object ObjectExample { fun hello(): String { return "hello" } + + override fun toString(): String { + return "Hello, it's me, ${ObjectExample::class.simpleName}" + } } -fun useObject() { - ObjectExample.hello() - val someRef: Any = ObjectExample // we use objects name just as is + +fun useSingletonObject() { + println(ObjectExample.hello()) // => hello + // In Kotlin, "Any" is the root of the class hierarchy, just like "Object" is in Java + val someRef: Any = ObjectExample + println(someRef) // => Hello, it's me, ObjectExample } + +/* The not-null assertion operator (!!) converts any value to a non-null type and +throws an exception if the value is null. +*/ +var b: String? = "abc" +val l = b!!.length + +data class Counter(var value: Int) { + // overload Counter += Int + operator fun plusAssign(increment: Int) { + this.value += increment + } + + // overload Counter++ and ++Counter + operator fun inc() = Counter(value + 1) + + // overload Counter + Counter + operator fun plus(other: Counter) = Counter(this.value + other.value) + + // overload Counter * Counter + operator fun times(other: Counter) = Counter(this.value * other.value) + + // overload Counter * Int + operator fun times(value: Int) = Counter(this.value * value) + + // overload Counter in Counter + operator fun contains(other: Counter) = other.value == this.value + + // overload Counter[Int] = Int + operator fun set(index: Int, value: Int) { + this.value = index + value + } + + // overload Counter instance invocation + operator fun invoke() = println("The value of the counter is $value") + +} +/* You can also overload operators through extension methods */ +// overload -Counter +operator fun Counter.unaryMinus() = Counter(-this.value) + +fun operatorOverloadingDemo() { + var counter1 = Counter(0) + var counter2 = Counter(5) + counter1 += 7 + println(counter1) // => Counter(value=7) + println(counter1 + counter2) // => Counter(value=12) + println(counter1 * counter2) // => Counter(value=35) + println(counter2 * 2) // => Counter(value=10) + println(counter1 in Counter(5)) // => false + println(counter1 in Counter(7)) // => true + counter1[26] = 10 + println(counter1) // => Counter(value=36) + counter1() // => The value of the counter is 36 + println(-counter2) // => Counter(value=-5) +} ``` ### Further Reading * [Kotlin tutorials](https://kotlinlang.org/docs/tutorials/) -* [Try Kotlin in your browser](http://try.kotlinlang.org/) +* [Try Kotlin in your browser](https://play.kotlinlang.org/) * [A list of Kotlin resources](http://kotlin.link/) |