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Kotlin Reference (一) Basic Syntax

KotLin 相干文档

官方在线Reference
kotlin-docs.pdf
Kotlin for android Developers 中文翻译
Kotlin开发工具集成,相干平台支撑指南
Kotlin开源项目与Libraries
Kotlin开源项目、资本、册本及课程搜刮平台

根本语法示例

(most from kotlin-docs.pdf)

package com.stone.basic.syntax/** * desc  : * author: stone * email : aa86799@163.com * time  : 27/05/2017 11 01 */class BasicSyntax {    //Function having two Int parameters with Int return type:    public fun sum(a: Int, b: Int): Int {//拜访润色符 省略时,默许为 public        return a + b    }    //Function having three Int parameters with Int return type:    fun sum(a: Int, b: Int, c: Int) = a + b + c    //Function returning no meaningful value:    fun printSum(a: Int, b: Int): Unit {//Unit为无范例,近似java中的void,可以省略        println("sum of " + a + " and " + b + " is ${a + b}")        println("sum of $a and $b is ${a + b}") //在双引号中 间接用 $符操纵变量   与上句等价    }    fun assignVarible() {        val a: Int = 1 // immediate assignment    val = 当地只读变量 即不可变 immutable        val b = 2 // `Int` type is inferred  主动范例揣度        val c: Int // Type required when no initializer is provided        c = 3 // deferred assignment        var x = 1 // Mutable variable:        x++        val s1 = "x is $x"  // simple name in template:        val s2 = "${s1.replace("is", "was")}, but now is $x" // arbitrary expression in template:        println(s2)    }    fun maxOf(a: Int, b: Int): Int {//        return a > b ? a : b; //原java中的三目运算符 不可用        if (a > b) return a        else return b    }    //fun maxOf(a:Int, b: Int):Int    fun minOf(a: Int, b: Int): Int = if (a < b) a else b    //字符串转int    private fun parseInt(str: String): Int? {// ? 暗示可认为空        return str.toIntOrNull(8)//参数为 进制数(radix), 不传默许为10   变换毛病 前往null    }    fun getBaseSyntax(name: String?): BasicSyntax? { // ? 暗示可认为空//        checkNotNull(name) // 参数不能够为空的 检测函数        return BasicSyntax()    }    fun printProduct(arg1: String, arg2: String) {        val x1 = parseInt(arg1)        val x2 = parseInt(arg2)        if (x1 == null) return        if (x2 == null) return        println(x1 * x2)    }    //is operator    fun getStringLength1(obj: Any): Int? { //Any 是任何Kotlin类的超类        if (obj is String) {// 近似java中的 instanceof// `obj` is automatically cast to `String` in this branch            return obj.length        }// `obj` is still of type `Any` outside of the type-checked branch        return null    }    // !is    fun getStringLength2(obj: Any): Int? {        if (obj !is String) return null        return obj.length    }    fun getStringLength3(obj: Any): Int? {        if (obj is String && obj.length > 0)            return obj.length        return null    }    //Using a for loop    fun foreachItems() {//        val items = listOf<String>("apple", "banana", "kiwi")        val items = listOf("apple", "banana", "kiwi")        for (item in items) {//in operator            println("item is $item")        }        for (index in items.indices) {//indices 索引  type: Collection//            println("item at $index is ${items.get(index)}")            println("item at $index is ${items[index]}") //运用[index]  而不消 .get(index)        }    }    //Using when expression    fun describe(obj: Any): String =            when (obj) {//when 中 必需 有一个else                1 -> "One"                "Hello" -> "Greeting"                is Long -> "Long"                !is String -> "not a string"                else -> "Unknown"            }    //Using ranges  假如在if中 check的是一个数值,且运用了 in operator    fun range() {        val x = 10; val y = 9  //同一行中运用 ; 来分开        if (x in 1..y + 1) {//运用 .. 来暗示局限   末了变换成 x in 1..10//        if (x in (1..(y + 1))) {//云云说明 履行按次 没成绩  末了变换成 x in 1..10//        if (x in ((1..y) + 1)) {云云说明 履行按次 不可   末了变换成  x in 10            println("fits in range")        }        for (x in 1..5) {//include 5        }        for (x in 1..10 step 2) {//x+=2   x is in {1, 3, 5, 7, 9}            println("rang 1..10 step 2: $x")        }        for (x in 9 downTo 0 step 3) {//x=9, x>=0 x-=3            println("x in 9 downTo 0 step 3: $x")        }        for (x in 0 until 10 step 2) {//until 10 : not include 10            println("x in 1 until 10: $x")        }    }    //Checking if a collection contains an object using in operator:    fun contains() {        val list = listOf("a1", "a2", "a3") //不可变list        when {// 婚配到一个前提 别的 就不再婚配            "a4" in list -> println("壹")            "a5" in list -> println(list.size)            "a3" in list -> println("the index is ${list.indexOf("a3")}")        }    }    //Using lambda expressions to filter and map collections:    fun collectionsLambda() {//        val list = mutableListOf<Int>()  //可变list//        for (i in 1 ..10) {//            list.add(i)////        }        val list = (1..10).toList() //上面的 简写        list.filter { it % 2 == 0 }.map { it * 3 }.forEach(::println)//      list.filter { it % 2 == 0 }.map { it * 3 }.forEach{ println("item is $it")}    }}fun main(args: Array<String>) {    var base = BasicSyntax()    base.printSum(10, 20)    base.assignVarible()    var min = base.minOf(10, 20)    println("min number is $min")    base.getBaseSyntax(null)    base.printProduct("1", "kk")    base.printProduct("33", "66")    println(null) //间接输入了 null 字符串    base.foreachItems()    println(base.describe(2))    base.range()    base.contains()    base.collectionsLambda()}

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