Kotlin 备忘清单是 Kotlin 编程语言的单页参考表
+fun main() {
+ // Code goes here
+}
+main() 函数是每个 Kotlin 程序的起点，在执行之前必须包含在代码中
+println("Greetings, earthling!")
+print("Take me to ")
+print("your leader.")
+
+/*
+打印:
+Greetings, earthling!
+Take me to your leader.
+*/
+// 这是单行注释
+
+/*
+这个
+注释
+用于
+多
+行
+*/
+fun main() {
+ println("I will be printed first.")
+ println("I will be printed second.")
+ println("I will be printed third.")
+}
+var age = 25
+age = 26
+val goldenRatio = 1.618
+// 以下变量在双引号内分配了一个文本值
+// 因此推断的类型是 String
+
+var color = "Purple"
+var streetAddress = "123 Main St."
+var cityState = "Brooklyn, NY"
+
+println(streetAddress + " " + cityState)
+// 打印: 123 Main St. Brooklyn, NY
+var address = "123 Main St."
+println("The address is $address")
+// 打印: The address is 123 Main St.
+var monument = "the Statue of Liberty"
+
+println(monument.capitalize())
+// 打印: The Statue of Liberty
+println(monument.length)
+// 打印: 21
+print("\"Excellent!\" I cried. \"Elementary,\" said he.")
+
+// 打印: "Excellent!" I cried. "Elementary," said he.
+\n 插入新行\t 插入标签\r 插入回车\' 插入单引号\" 插入双引号\\ 插入反斜杠\$ 插入美元符号5 + 7 // 12
+9 - 2 // 7
+8 * 4 // 32
+25 / 5 // 5
+31 % 2 // 1
++ 加法、- 减法、* 乘法、/ 除法和 % 模数
5 + 8 * 2 / 4 - 3 // 6
+3 + (4 + 4) / 2 // 7
+4 * 2 + 1 * 7 // 15
+3 + 18 / 2 * 1 // 12
+6 - 3 % 2 + 2 // 7
+var batteryPercentage = 80
+
+// 长语法
+batteryPercentage = batteryPercantage + 10
+
+// 带有增广赋值运算符的短句法
+batteryPercentage += 10
+var year = 2019
+year++ // 2020
+year-- // 2019
+Math.pow(2.0, 3.0) // 8.0
+Math.min(6, 9) // 6
+Math.max(10, 12) // 12
+Math.round(13.7) // 14
+var morning = true
+
+if (morning) {
+ println("Rise and shine!")
+}
+// 打印: Rise and shine!
+var rained = false
+
+if (rained) {
+ println("今天不需要给植物浇水。")
+} else {
+ println("植物需要浇水！")
+}
+// 打印: 植物需要浇水！
+var age = 65
+
+if (age < 18 ) {
+ println("您被视为未成年人")
+} else if (age < 60) {
+ println("您被视为成年人")
+} else {
+ println("你被认为是高级")
+}
+
+// 打印: 你被认为是高级
+var myAge = 19
+var sisterAge = 11
+var cousinAge = 11
+
+myAge > sisterAge // true
+myAge < cousinAge // false
+myAge >= cousinAge // true
+myAge <= sisterAge // false
+var humid = true
+var raining = true
+var jacket = false
+
+println(!humid)
+// 打印: false
+println(jacket && raining)
+// 打印: true
+println(humid || raining)
+// 打印: true
+var humid = true
+var raining = true
+var shorts = false
+var sunny = false
+
+// true AND true
+println(humid && raining) // true
+// true AND false
+println(humid && shorts) // false
+// false AND true
+println(sunny && raining) // false
+// false AND false
+println(shorts && sunny) // false
+var late = true
+var skipBreakfast = true
+var underslept = false
+var checkEmails = false
+
+// true OR true
+println(skipBreakfast || late) // true
+// true OR false
+println(late || checkEmails) // true
+// false OR true
+println(underslept || late) // true
+// false OR false
+println(checkEmails || underslept) // false
+var hungry = true
+var full = false
+
+println(!hungry) // false
+println(!full) // true
+!true && (false || true) // false
+/*
+(false || true) 被评估首先返回 true。
+然后，评估 !true && true 并返回最终结果 false
+*/
+
+!false && true || false // true
+/*
+!false 被评估首先返回 true。
+然后评估 true && true，返回 true。
+那么，真|| 评估 false 最终返回 true
+*/
+var studied = true
+var wellRested = true
+
+if (wellRested) {
+ println("祝你今天好运！")
+ if (studied) {
+ println("你应该为考试做好准备！")
+ } else {
+ println("考试前花几个小时学习！")
+ }
+}
+
+// 打印: 祝你今天好运！
+// 打印: 你应该为考试做好准备！
+var grade = "A"
+
+when(grade) {
+ "A" -> println("很棒的工作！")
+ "B" -> println("做得太好了！")
+ "C" -> println("你通过了！")
+ else -> println("关！下次一定要多准备！")
+}
+// 打印: 很棒的工作！
+var height = 46 // inches
+
+if (height in 1..53) {
+ println("抱歉，您必须至少 54 英寸才能乘坐过山车"）
+}
+// Prints: 抱歉，您必须至少 54 英寸才能乘坐过山车
+var myAge = 22
+var sisterAge = 21
+
+myAge == sisterAge // false
+myAge !== sisterAge // true
+var programmingLanguages = listOf("C#", "Java", "Kotlin", "Ruby")
+var fruits = mutableListOf("Orange", "Apple", "Banana", "Mango")
+var cars = listOf("BMW", "Ferrari", "Volvo", "Tesla")
+
+println(cars[2]) // Prints: Volvo
+var worldContinents = listOf("Asia", "Africa", "North America", "South America", "Antarctica", "Europe", "Australia")
+
+println(worldContinents.size) // Prints: 7
+var seas = listOf("Black Sea", "Caribbean Sea", "North Sea")
+println(seas.contains("North Sea")) // Prints: true
+
+// contains() 函数对任何列表执行读取操作并确定元素是否存在
+seas.add("Baltic Sea") // 错误：无法对不可变列表执行写操作
+// add() 函数只能在可变列表上调用，因此上面的代码会引发错误
+var primaryColors = setOf("Red", "Blue", "Yellow")
+var womenInTech = mutableSetOf("Ada Lovelace", "Grace Hopper", "Radia Perlman", "Sister Mary Kenneth Keller")
+var companies = setOf("Facebook", "Apple", "Netflix", "Google")
+
+println(companies.elementAt(3))
+// Prints: Google
+println(companies.elementAt(4))
+// Returns and Error
+println(companies.elementAtOrNull(4))
+// Prints: null
+var averageTemp = mapOf("winter" to 35, "spring" to 60, "summer" to 85, "fall" to 55)
+var europeanDomains = mutableMapOf("Germany" to "de", "Slovakia" to "sk", "Hungary" to "hu", "Norway" to "no")
+var oscarWinners = mutableMapOf("Parasite" to "Bong Joon-ho", "Green Book" to "Jim Burke", "The Shape Of Water" to "Guillermo del Toro")
+
+println(oscarWinners.keys)
+// Prints: [Parasite, Green Book, The Shape Of Water]
+
+println(oscarWinners.values)
+// Prints: [Bong Joon-ho, Jim Burke, Guillermo del Toro]
+
+println(oscarWinners["Parasite"])
+// Prints: Bong Joon-ho
+var worldCapitals = mutableMapOf("United States" to "Washington D.C.", "Germany" to "Berlin", "Mexico" to "Mexico City", "France" to "Paris")
+
+worldCapitals.put("Brazil", "Brasilia")
+println(worldCapitals)
+// Prints: {United States=Washington D.C., Germany=Berlin, Mexico=Mexico City, France=Paris, Brazil=Brasilia}
+
+worldCapitals.remove("Germany")
+println(worldCapitals)
+// Prints: {United States=Washington D.C., Mexico=Mexico City, France=Paris, Brazil=Brasilia}
+fun greet() {
+ println("Hey there!")
+}
+
+fun main() {
+ // Function call
+ greet() // Prints: Hey there!
+}
+fun birthday(name: String, age: Int) {
+ println("Happy birthday $name! You turn $age today!")
+}
+
+fun main() {
+ birthday("Oscar", 26)
+ // Prints: Happy birthday Oscar! You turn 25 today!
+ birthday("Amarah", 30)
+ // Prints: Happy birthday Amarah! You turn 30 today!
+}
+fun favoriteLanguage(name, language = "Kotlin") {
+ println("Hello, $name. Your favorite programming language is $language")
+}
+
+fun main() {
+ favoriteLanguage("Manon")
+ // Prints: Hello, Manon. Your favorite programming language is Kotlin
+
+ favoriteLanguage("Lee", "Java")
+ // Prints: Hello, Lee. Your favorite programming language is Java
+}
+fun findMyAge(currentYear: Int, birthYear: Int) {
+ var myAge = currentYear - birthYear
+ println("I am $myAge years old.")
+}
+
+fun main() {
+ findMyAge(currentYear = 2020, birthYear = 1995)
+ // Prints: I am 25 years old.
+ findMyAge(birthYear = 1920, currentYear = 2020)
+ // Prints: I am 100 years old.
+}
+// Return type is declared outside the parentheses
+fun getArea(length: Int, width: Int): Int {
+ var area = length * width
+
+ // return statement
+ return area
+}
+
+fun main() {
+ var myArea = getArea(10, 8)
+ println("The area is $myArea.")
+ // Prints: The area is 80.
+}
+fun fullName(firstName: String, lastName: String) = "$firstName $lastName"
+
+fun main() {
+ println(fullName("Ariana", "Ortega"))
+ // Prints: Ariana Ortega
+ println(fullName("Kai", "Gittens"))
+ // Prints: Kai Gittens
+}
+fun main() {
+ // Anonymous Function:
+ var getProduct = fun(num1: Int, num2: Int): Int {
+ return num1 * num2
+ }
+ println(getProduct(8, 3))
+ // Prints: 24
+
+ // Lambda Expression
+ var getDifference = { num1: Int, num2: Int -> num1 - num2 }
+ println(getDifference(10, 3))
+ // Prints: 7
+}
+// 具有包含默认值的属性的类
+class Student {
+ var name = "Lucia"
+ var semester = "Fall"
+ var gpa = 3.95
+}
+
+// 没有类体的简写语法
+class Student
+// Class
+class Student {
+ var name = "Lucia"
+ var semester = "Fall"
+ var gpa = 3.95
+}
+
+fun main() {
+ var student = Student()
+ // Instance
+ println(student.name)
+ // Prints: Lucia
+ println(student.semester)
+ // Prints: Fall
+ println(student.gpa)
+ // Prints: 3.95
+}
+class Student(val name: String, val gpa: Double, val semester: String, val estimatedGraduationYear: Int)
+
+fun main() {
+ var student = Student("Lucia", 3.95, "Fall", 2022)
+ println(student.name)
+ // Prints: Lucia
+ println(student.gpa)
+ // Prints: 3.95
+ println(student.semester)
+ // Prints: Fall
+ println(student.estimatedGraduationYear)
+ // Prints: 2022
+}
+class Student(val name: String, val gpa: Double, val semester: String, val estimatedGraduationYear: Int) {
+ init {
+ println("$name has ${estimatedGraduationYear - 2020} years left in college.")
+ }
+}
+
+fun main() {
+ var student = Student("Lucia", 3.95, "Fall", 2022)
+ // Prints: Lucia has 2 years left in college.
+}
+class Student(val name: String, val gpa: Double, val semester: String, val estimatedGraduationYear: Int) {
+
+ init {
+ println("$name has ${estimatedGraduationYear - 2020} years left in college.")
+ }
+
+ // 成员函数
+ fun calculateLetterGrade(): String {
+ return when {
+ gpa >= 3.0 -> "A"
+ gpa >= 2.7 -> "B"
+ gpa >= 1.7 -> "C"
+ gpa >= 1.0 -> "D"
+ else -> "E"
+ }
+ }
+}
+
+// 创建实例并调用函数时，将执行 when 表达式并返回字母等级
+fun main() {
+ var student = Student("Lucia", 3.95, "Fall", 2022)
+ // Prints: Lucia has 2 years left in college.
+ println("${student.name}'s letter grade is ${student.calculateLetterGrade()}.")
+ // Prints: Lucia's letter grade is A.
+}
+