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基本语法 ​

包的定义与导出 ​

kotlin
package org.kotlin
import kotlin.test.*
//  ......
package org.kotlin
import kotlin.test.*
//  ......

程序入口 ​

Kotlin程序入口是main函数

kotlin
fun main() {
    println("Hello world!")
}
fun main() {
    println("Hello world!")
}

支持自动推断

kotlin
fun sum(a: Int, b: Int) = a + b
fun sum(a: Int, b: Int) = a + b

返回无意义的值，Unit可以省略

kotlin
fun printSum(a: Int, b: Int): Unit {
    println("$a + $b is ${a + b}")
}
fun printSum(a: Int, b: Int): Unit {
    println("$a + $b is ${a + b}")
}

函数 ​

kotlin
fun sum(a: Int, b: Int): Int {
    return a + b
}
fun sum(a: Int, b: Int): Int {
    return a + b
}

注释 ​

kotlin
// 单行注释
/* 多行
注释 */
// 单行注释
/* 多行
注释 */

Kotlin变量 ​

局部变量可以用关键字val定义，如果是可变的可以用var

kotlin
val a: Int = 0
val b = 1
val c: Int
c = 2
val a: Int = 0
val b = 1
val c: Int
c = 2
kotlin
var x = 5
x += 1
var x = 5
x += 1

字符串模版 ​

kotlin
var a = 1
val s1 = "a is $a" 

a = 2
val s2 = "${s1.replace("is", "was")}, but now is $a"
var a = 1
val s1 = "a is $a" 

a = 2
val s2 = "${s1.replace("is", "was")}, but now is $a"

if条件语句 ​

kotlin
fun maxOf(a: Int, b: Int): Int {
    if (a > b) {
        return a
    } else {
        return b
    }
}
fun maxOf(a: Int, b: Int): Int {
    if (a > b) {
        return a
    } else {
        return b
    }
}

if表达式

kotlin
fun maxOf(a: Int, b: Int) = if (a > b) a else b
fun maxOf(a: Int, b: Int) = if (a > b) a else b

for循环 ​

kotlin
val nums = listOf("one", "two", "three")
for (num in nums) {
    println(num)
}
val nums = listOf("one", "two", "three")
for (num in nums) {
    println(num)
}

while循环 ​

kotlin
val nums = listOf("one", "two", "three")
var index = 0
while (index < nums.size) {
    println("num at $index is ${nums[index]}")
    index++
}
val nums = listOf("one", "two", "three")
var index = 0
while (index < nums.size) {
    println("num at $index is ${nums[index]}")
    index++
}

when表达式 ​

kotlin
fun describe(obj: Any): String =
    when (obj) {
        1          -> "One"
        "Hello"    -> "Greeting"
        is Long    -> "Long"
        !is String -> "Not a string"
        else       -> "Unknown"
    }
fun describe(obj: Any): String =
    when (obj) {
        1          -> "One"
        "Hello"    -> "Greeting"
        is Long    -> "Long"
        !is String -> "Not a string"
        else       -> "Unknown"
    }

range区间 ​

kotlin
val x = 10
val y = 9
if (x in 1..y+1) {
    println("fits in range")
}
val x = 10
val y = 9
if (x in 1..y+1) {
    println("fits in range")
}

集合 ​

kotlin
val nums = listOf("one", "two", "three")
for (num in nums) {
    println(num)
}
val nums = listOf("one", "two", "three")
for (num in nums) {
    println(num)
}

详细了解可通过 Kotlin基本语法

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