Kotlin 学习笔记
原视频资料地址
你好世界
fun main(args: Array<String>) {
println("Hello, Kotlin!")
}
数据类型
数据类型
数据类型
fun main(args: Array<String>) {
val aByte:Byte=Byte.MAX_VALUE
val bByte:Byte=Byte.MIN_VALUE
println("MAX_VALUE is $aByte, MIN_VALUE is $bByte")
val aInt:Int = 0b011 // 二进制
println("aInt is $aInt")
}
输出
MAX_VALUE is 127, MIN_VALUE is -128
aInt is 3
初识函数
fun main(args: Array<String>) {
printOneStar()
printThreeStars()
printFiveStars()
println("*******")
printFiveStars()
printThreeStars()
printOneStar()
}
fun printOneStar() {
println(" * ")
}
fun printThreeStars() {
println(" *** ")
}
fun printFiveStars() {
println(" ***** ")
}
输出
*
***
*****
*******
*****
***
*
Boolean
fun main(args: Array<String>) {
val num1 = Math.sqrt(5.0) - Math.sqrt(4.0)
val num2 = Math.sqrt(4.0) - Math.sqrt(3.0)
println(num1 > num2)
val num3 = Math.pow(2.0, 100.0)
val num4 = Math.pow(3.0, 75.0)
println(num3 > num4)
}
输出
false
false
函数作业练习
fun sayHello(name: String) = "Hello $name"
fun checkAge(age: Int) = age > 18
fun saveLog(logLevel: Int) {}
fun main(args: Array<String>) {
println(sayHello("Leo"))
println(checkAge(2))
saveLog(1)
}
输出
Hello Leo
false
字符串
fun main(args: Array<String>) {
val template = """
|今天
|明天
""".trimMargin("|")
println(template)
val template2 = "今天\n明天"
println(template2)
}
输出
今天
明天
今天
明天
字符串比较
fun main(args: Array<String>) {
var str1 = "123"
var str2 = "123"
println(str1 == str2)
println(str1.equals(str2))
str1 = "ABC"
str2 = "abc"
println()
println(str1 == str2)
println(str1.equals(str2))
println(str1.equals(str2, true)) // ignoreCase: true
}
输出
true
true
false
false
true
空值处理
fun main(args: Array<String>) {
println(heat("水"))
println(heat(null))
}
fun heat(str: String?): String {
return if (str == null) "不加热" else "加热$str"
}
输出
加热水
不加热
When表达式
fun gradeStudent(score: Int) = when(score) {
10 -> println("Great")
9 -> println("Nice")
8 -> println("Better")
7 -> println("Fine")
6 -> println("Ok")
else -> println("Bad")
}
fun main(args: Array<String>) {
gradeStudent(7)
}
输出
Fine
循环和范围
fun main(args: Array<String>) {
val nums = 1..100 // [1, 100]
nums.map { it -> println(it) }
val nums2 = 1 until 100 // [1, 100)
nums2.map { it -> println(it) }
val nums3 = 1..100 step 2
nums3.map { println(it) }
nums3.reversed().map { println(it) }
println("total: ${nums3.count()}")
val nums4 = 100 downTo 1
nums4.map { println(it) }
}
List
fun main(args: Array<String>) {
val lists = listOf("a", "b", "c", "d")
lists.map { println(it) }
for ((i, e) in lists.withIndex()) {
println("$i is $e")
}
}
输出
a
b
c
d
0 is a
1 is b
2 is c
3 is d
Map
import java.util.*
fun main(args: Array<String>) {
val map = TreeMap<String, String>()
map["1"] = "good"
map["2"] = "better"
println(map["2"])
val map2 = mapOf("1" to "good", "2" to "better")
println(map2["1"])
}
输出
better
good
函数表达式
fun main(args: Array<String>) {
val i = { x: Int, y: Int -> x + y }
println(i(3, 5))
println(add(4, 5))
val j: (Int, Int) -> Int = { x, y -> x + y }
println(j(4, 5))
}
fun add(x: Int, y: Int) = x + y
输出
8
9
9
默认参数和具名参数
import kotlin.math.PI
fun getCirclePerimeter(pi: Double = PI,radius: Double) = 2 * pi * radius
fun getCirclePerimeter2(pi: Double = PI, diameter:Double) = pi * diameter
fun main(args: Array<String>) {
println(getCirclePerimeter(radius = 2.0))
println(getCirclePerimeter2(diameter = 4.0))
}
输出
12.566370614359172
12.566370614359172
字符串和数字之间的转换
fun main(args: Array<String>) {
var a = "13"
var b = 13
a = b.toString()
b = a.toInt()
var c = "${a}3"
b = c.toInt()
println(b)
}
输出
133
人机交互-打字交互
fun main(args: Array<String>) {
println("First NUM:")
val num1str = readLine()
println("Second NUM:")
val num2str = readLine()
val num1 = num1str!!.toInt()
val num2 = num2str!!.toInt()
println("$num1 + $num2 = ${num1 + num2}")
}
输出
First NUM:
12
Second NUM:
13
12 + 13 = 25
异常处理
fun main(args: Array<String>) {
println("First NUM:")
val num1str = readLine()
println("Second NUM:")
val num2str = readLine()
try {
val num1 = num1str!!.toInt()
val num2 = num2str!!.toInt()
println("$num1 + $num2 = ${num1 + num2}")
} catch (e: NumberFormatException) {
println("Wrong Number Type")
}
}
输出
First NUM:
a
Second NUM:
b
Wrong Number Type
递归
fun main(args: Array<String>) {
println(fact(6))
}
fun fact(num: Int): Int = if (num == 1) 1 else num * fact(num - 1)
输出
720
BigInteger改写
import java.math.BigInteger
fun main(args: Array<String>) {
println(fact(BigInteger("100")))
}
fun fact(num: BigInteger): BigInteger = if (num == BigInteger.ONE) BigInteger.ONE else num * fact(num - BigInteger.ONE)
输出
93326215443944152681699238856266700490715968264381621468592963895217599993229915608941463976156518286253697920827223758251185210916864000000000000000000000000
尾递归优化
fun main(args: Array<String>) {
println(tailrecAdd(100, 0))
}
tailrec fun tailrecAdd(num: Int, result: Int): Int = if (num == 0) result else tailrecAdd(num - 1, result + num)
输出
5050
初识面向对象
class Rect(val height: Int, val width: Int)
fun main(args: Array<String>) {
val rect = Rect(10, 20)
println("Height is ${rect.height}")
println("Width is ${rect.width}")
}
输出
Height is 10
Width is 20
静态属性和动态行为
class Girl(val character: String, val voice: String) {
private fun smile() {
println("Smile")
}
fun laugh() {
smile()
println("Ha Ha")
}
}
fun main(args: Array<String>) {
val girl = Girl("Good", "Great")
girl.laugh()
}
输出
Smile
Ha Ha
洗衣机实例
class WashMachine(val module: String, var size: Int) {
private var isDoorOpen = false
fun openDoor() {
isDoorOpen = true
println("Door is opened.")
}
fun closeDoor() {
isDoorOpen = false
println("Door is closed.")
}
fun start() {
if (isDoorOpen) {
println("Close the door first, please.")
} else {
println("Start working.")
}
}
}
fun main(args: Array<String>) {
var machine01 = WashMachine("小天鹅", 10)
machine01.openDoor()
machine01.start()
machine01.closeDoor()
machine01.start()
}
输出
Door is opened.
Close the door first, please.
Door is closed.
Start working.
封装
private关键字
继承
Father.kt
open class Father {
var character: String = "内向"
open fun action() {
println("公共场合大声喧哗")
}
}
Son.kt
class Son : Father() {
override fun action() {
println("公共场合很有礼貌")
}
}
Test.kt
fun main(args: Array<String>) {
val son1 = Son()
println("The character is ${son1.character}")
son1.action()
}
输出
The character is 内向
公共场合很有礼貌
抽象类和继承
Human.kt
abstract class Human(var name: String) {
abstract fun eat()
}
Man.kt
class Man(name: String) : Human(name) {
override fun eat() {
println("$name 大口吃")
}
}
'Woman.kt`
class Woman(name: String) : Human(name) {
override fun eat() {
println("$name 小口吃")
}
}
Test.kt
fun main(args: Array<String>) {
val man = Man("Maximus")
val woman = Woman("Ivy")
man.eat()
woman.eat()
}
输出
Maximus 大口吃
Ivy 小口吃
抽象类和接口
- 接口是事物的能力
- 抽象类是事物的本质
Human.kt
abstract class Human(var name: String) {
abstract fun eat()
}
InterfaceMan.kt
interface InterfaceMan {
fun action()
}
Test.kt
class PersonMan(name: String) : Human(name), InterfaceMan {
override fun eat() {
println("${name}大口吃饭")
}
override fun action() {
println("${name}长胡子")
}
}
fun main(args: Array<String>) {
val person = PersonMan("Maximus")
person.eat()
person.action()
}
输出
Maximus大口吃饭
Maximus长胡子
区别：抽象类是事物的本质，是一类事物都具备的东西；接口是事物的能力，只有一类中的一部分事物才具备这种能力。
委托和代理
by关键字
IWashBowl.kt
interface IWashBowl {
fun washing()
}
BigHeadSon.kt
class BigHeadSon : IWashBowl {
override fun washing() {
println("我是大头儿子，我在开心得洗碗，一次一块钱")
}
}
SmallHeadFather.kt
class SmallHeadFather : IWashBowl by BigHeadSon()
Test.kt
fun main(args: Array<String>) {
val fa = SmallHeadFather()
fa.washing()
}
输出
我是大头儿子，我在开心得洗碗，一次一块钱
单例模式
IWashBowl.kt
interface IWashBowl {
fun washing()
}
BigHeadSon.kt
object BigHeadSon : IWashBowl {
override fun washing() {
println("我是大头儿子，我在开心得洗碗，一次一块钱")
}
}
SmallHeadFather.kt
class SmallHeadFather : IWashBowl by BigHeadSon { // 注意区别，没有括号
override fun washing() {
println("我是小头爸爸，我让我儿子洗碗")
BigHeadSon.washing() // 区别，没有括号
}
}
Test.kt
fun main(args: Array<String>) {
val fa = SmallHeadFather()
fa.washing()
}
输出
我是小头爸爸，我让我儿子洗碗
我是大头儿子，我在开心得洗碗，一次一块钱
枚举类
enum class Week {
Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday
}
fun main(args: Array<String>) {
println(Week.Monday)
println(Week.Monday.ordinal)
Week.values().filter { it.toString().startsWith("S") && it.toString().contains("n") }.map { println(it) }
Week.values().asList().also(::println)
}
输出
Monday
1
Sunday
[Sunday, Monday, Tuesday, Wednesday, Thursday, Friday, Saturday]
密封类
作用：定义子类类型有限的类
密封类和枚举类的区别：密封类更在意类型；枚举类更在意数据
sealed class Animal {
class Fish : Animal()
class Dog : Animal()
class Cat : Animal()
}
fun main(args: Array<String>) {
val type01 = Animal.Fish()
val type02 = Animal.Dog()
val type03 = Animal.Cat()
sayHello(type01)
sayHello(type02)
sayHello(type03)
}
fun sayHello(animal: Animal) = when (animal) {
is Animal.Fish -> println("Hello Fish")
is Animal.Dog -> println("Hello Dog")
is Animal.Cat -> println("Hello Cat")
}
输出
Hello Fish
Hello Dog
Hello Cat
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