Kotlin 基本语法实例详解
程序员文章站
2023-12-20 12:37:46
基本语法示例
实例代码:
package com.stone.basic.syntax
/**
* desc :
* author: stone...
基本语法示例
实例代码:
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 {//访问修饰符 省略时,默认为 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为无类型,类似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 直接用 $符操作变量 与上句等价 } fun assignvarible() { val a: int = 1 // immediate assignment val = 本地只读变量 即不可变 immutable val b = 2 // `int` type is inferred 自动类型推断 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? {// ? 表示可以为空 return str.tointornull(8)//参数为 进制数(radix), 不传默认为10 转换错误 返回null } fun getbasesyntax(name: string?): basicsyntax? { // ? 表示可以为空 // checknotnull(name) // 参数不能为空的 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) {// 类似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]}") //使用[index] 而不用 .get(index) } } //using when expression fun describe(obj: any): string = when (obj) {//when 中 必须 有一个else 1 -> "one" "hello" -> "greeting" is long -> "long" !is string -> "not a string" else -> "unknown" } //using ranges 如果在if中 check的是一个数值,且使用了 in operator fun range() { val x = 10; val y = 9 //同一行中使用 ; 来分隔 if (x in 1..y + 1) {//使用 .. 来表示范围 最后转换成 x in 1..10 // if (x in (1..(y + 1))) {//如此解释 执行顺序 没问题 最后转换成 x in 1..10 // if (x in ((1..y) + 1)) {如此解释 执行顺序 不行 最后转换成 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 {// 匹配到一个条件 其它 就不再匹配 "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) //直接输出了 null 字符串 base.foreachitems() println(base.describe(2)) base.range() base.contains() base.collectionslambda() }
感谢阅读,希望能帮助到大家,谢谢大家对本站的支持!