Kotlin 基础(TeamCity Pipeline 用)

TeamCity 的 pipeline 配置用 Kotlin DSL 写,所以先把 Kotlin 语言基础过一遍。参考 Kotlin Tour。

IDE 用 IntelliJ IDEA 或 VSCode。本地 TeamCity server 的 DSL 文档一直挂在 <TeamCity_server_URL>/app/dsl-documentation/index.html。

变量

val 只读,var 可变。

val a = 1 // read-only variables
var b = 2 // mutable variables
b=3
println("a = ${a}") // a = 1

类型

类别	基本类型
整数	Byte, Short, Int, Long
无符号整数	UByte, UShort, UInt, ULong
浮点数	Float, Double
布尔	Boolean
字符	Char
字符串	String

声明可以分三种:只声明不初始化、显式标类型并初始化、初始化但不写类型(类型推断)。

fun main() {
    // Variable declared without initialization
    val d: Int
    // Variable initialized
    d = 3

    // Variable explicitly typed and initialized
    val e: String = "hello"

    //Variable initialization without type
    val c = 3.12

    // Variables can be read because they have been initialized
    println(d) // 3
    println(e) // hello
    println(c) // 3.12
}

可空类型

类型后加 ? 表示可空。

fun main() {
    var a: String? = null
    println(a) // null

    // nullable has nullable String type
    var nullable: String? = "You can keep a null here"

    // This is OK
    nullable = null // null
    nullable = "test" // test

    println(nullable)
}

运算符

复合赋值 +=, -=, *=, /=, %=:

var customers = 10

// Some customers leave the queue
customers = 8

customers = customers + 3 // Example of addition: 11
customers += 7            // Example of addition: 18
customers -= 3            // Example of subtraction: 15
customers *= 2            // Example of multiplication: 30
customers /= 3            // Example of division: 10

println(customers) // 10

集合

List

List 按添加顺序存元素,允许重复。listOf 只读,mutableListOf 可变。

// Read only list
val readOnlyShapes = listOf("triangle", "square", "circle")
println(readOnlyShapes) // [triangle, square, circle]

// Mutable list with explicit type declaration
// Restricting the type of element
var shapes: MutableList<String> = mutableListOf("triangle", "square", "circle")
println(shapes) // [triangle, square, circle]

// Mutable list without type
var shapes1 = mutableListOf("triangle", "square", "circle")
shapes1[1]="1"
println(shapes1) // [triangle, 1, circle]

常用函数:first() 第一个、last() 最后一个、count() 长度、add(item) 添加、remove(item) 删除(删第一个匹配)、filter(fn) 过滤、map(fn) 变换、fold(初始值, fn(x, item)) 从左到右累加。

println(listOf(1, 2, 3).fold(3, { x, item -> x *item })) // 18

用 in 判断元素是否在 list 里:

fun main() {
    val readOnlyShapes = listOf("triangle", "square", "circle")
    println("circle" in readOnlyShapes)// true
}

Set

Set 无序,只存唯一元素。setOf 只读,mutableSetOf 可变。常用函数 count()、add(item)、remove(item),同样用 in 判断:

fun main() {
    val readOnlyFruit = setOf("apple", "banana", "cherry", "cherry")
    println("banana" in readOnlyFruit) // true
}

Map

Map 存键值对,用 key 取 value。mapOf 只读,mutableMapOf 可变。

fun main() {
    // Read-only map
    val readOnlyJuiceMenu = mapOf("apple" to 100, "kiwi" to 190, "orange" to 100)
    println(readOnlyJuiceMenu)
    // {apple=100, kiwi=190, orange=100}

    // Mutable map with explicit type declaration
    val juiceMenu: MutableMap<String, Int> = mutableMapOf("apple" to 100, "kiwi" to 190, "orange" to 100)
    println(juiceMenu)
    // {apple=100, kiwi=190, orange=100}

    // Mutable map without type
    val juiceMenu1 = mutableMapOf("apple" to "test", "kiwi" to 190, "orange" to 100)
    println(juiceMenu1) //{apple=test, kiwi=190, orange=100}
}

常用函数:count() 长度、put(key, value) 添加、remove(key) 删除、containsKey(key) 判断键存在、keys 所有键、values 所有值。in 配合 .keys / .values 用:

fun main() {
    val readOnlyJuiceMenu = mapOf("apple" to 100, "kiwi" to 190, "orange" to 100)
    println("orange" in readOnlyJuiceMenu.keys)
    // true
    println(200 in readOnlyJuiceMenu.values)
    // false
}

控制流

if

val d: Int
val check = true

if (check) {
    d = 1
} else {
    d = 2
}

if 是表达式,可以当三元用:

println(if (a > b) a else b) // Returns a value: 2

when

类似 switch:

val obj = "Hello"

when (obj) {
    // Checks whether obj equals to "1"
    "1" -> println("One")
    // Checks whether obj equals to "Hello"
    "Hello" -> println("Greeting")
    // Default statement
    else -> println("Unknown")
}
// Greeting

val temp = 18

val description = when {
    // If temp < 0 is true, sets description to "very cold"
    temp < 0 -> "very cold"
    // If temp < 10 is true, sets description to "a bit cold"
    temp < 10 -> "a bit cold"
    // If temp < 20 is true, sets description to "warm"
    temp < 20 -> "warm"
    // Sets description to "hot" if no previous condition is satisfied
    else -> "hot"
}
println(description)

循环

for:

for (number in 1..5) {
    // number is the iterator and 1..5 is the range
    print(number)
}
// 12345
val cakes = listOf("carrot", "cheese", "chocolate")

for (cake in cakes) {
    println("Yummy, it's a $cake cake!")
}

while:

var cakesEaten = 0
while (cakesEaten < 3) {
    println("Eat a cake")
    cakesEaten++
}

do ... while:

var cakesEaten = 0
var cakesBaked = 0
do {
    println("Bake a cake")
    cakesBaked++
} while (cakesBaked < cakesEaten)

函数

fun sum(x: Int, y: Int): Int {
    return x + y
}

Lambda 表达式,形式 { 参数名: 类型 -> 表达式 } 或 { 参数名 -> 表达式 }:

println({ text: String -> text.uppercase() }("hello"))

val upperCaseString: (String) -> String = { text -> text.uppercase() }

fun main() {
    println(upperCaseString("hello"))
    // HELLO
}

类

class Contact(val id: Int, var email: String) {
    fun printId() {
        println(id)
    }
}

fun main() {
    val contact = Contact(1, "mary@gmail.com")
    // Calls member function printId()
    contact.printId()
    // 1
}

data class 自带几个方法:

方法	作用
.toString()	打印可读的实例字符串(含属性)
.equals() 或 ==	比较两个实例
.copy()	复制一个实例,可改部分属性

val user = User("Alex", 1)

// Automatically uses toString() function so that output is easy to read
println(user.toString())  // User(name=Alex, id=1)
println(user)  // User(name=Alex, id=1)
val user = User("Alex", 1)
val secondUser = User("Alex", 1)
val thirdUser = User("Max", 2)

// Compares user to second user
println("user == secondUser: ${user == secondUser}") // user == secondUser: true

// Compares user to third user
println("user == thirdUser: ${user.equals(thirdUser)}") // user == thirdUser: false
val user = User("Alex", 1)
val secondUser = User("Alex", 1)
val thirdUser = User("Max", 2)

// Creates an exact copy of user
println(user.copy())
// User(name=Alex, id=1)

// Creates a copy of user with name: "Max"
println(user.copy("Max"))
// User(name=Max, id=1)

// Creates a copy of user with id: 3
println(user.copy(id = 3))
// User(name=Alex, id=3)