简单的kotlin练习(ing)

fun main(args: Array<String>) {
println("Hello, world!")
}

fun main(args: Array<String>) {
if (args.size == 0) {
println("Please provide a name as a command-line argument")
return
}
println("Hello, ${args[0]}")
}

fun main(args: Array<String>) {
for (name in args) {
println("Hello, $name")
}
}

fun main(args: Array<String>) {
val language = if (args.size == 0) "EN" else args[0]
println(when (language) {
"EN" -> "Hello!"
"FR" -> "Salut!"
"IT" -> "Ciao"
else -> "Sorry, I can't greet you in $language yet"
})
for (name in args) {
println("Hello, $name")
}
}

class Greeter(val name: String) {
fun greet() {
println("Hello, ${name}")
}
}

fun main(args: Array<String>) {
Greeter(args[0]).greet()
}

fun main(args: Array<String>) {
println(max(args[0].toInt(), args[1].toInt))
}
fun max(a: Int, b: Int) = if (a > b) a else b

fun parseInt(str: String): Int? {
try {
return str.toInt()
} catch (e: NumberFormatException) {
println("One of the arguments isn't Int")
}
return null
}

fun main(args: Array<String>) {
if (args.size < 2) {
println("No number supplied")
} else {
val x = parseInt(args[0])
val y = parseInt(args[1])

if(x != null && y != null) {
println(x * y)
} else {
println("One of the arguments is null")
}
}
}

fun main(args: Array<String>) {
println(getStringLength("aaa"))
println(getStringLength(1))
}

fun getStringLength(obj: Any): Int? {
if (obj is String)
renturn obj.length
return null
}

fun main(args: Array<String>) {
var i = 0
while (i < args.size)
println(args[i++])
}

fun main(args: Array<String>) {
for (arg in args) {
println(arg)
}

//or
println()
println("===" + args.indices)
for (i in args.indices) {
println(args[i])
}
}

fun main(args: Array<String>) {
val x = args[0].toInt()
//check if a number lies within a range:
val y = 10
if (x in 1..y-1)
println("OK")

//Iterate over a range:
for (a in 1..5)
println("${a}  ")

//check if a number is out of range:
println()
val array = arrayListOf<String>()
//val array = ArrayList<String>()
array.add("aaa")
array.add("bbb")
array.add("ccc")

println("===" + x)
if (x !in 0..array.size -1)
println("Out: array has only ${array.size} elements. x = ${x}")

//check if a collection contains an object:
if ("aaa" in array) // collection.contains(obj) is called
println("Yes: array contains aaa")
if ("ddd" in array) // collection.contains(obj) is called
println("Yes: array contains aaa")
else
println("No: array doesn't contains ddd")
}

fun main(args: Array<String>) {
cases("Hello")
cases(1)
cases(0L)
cases(MyClass())
cases("hello")
}

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

class MyClass() {

}

/*See http://kotlinlang.org/docs/reference/multi-declarations.html#multi-declarations*/ fun main(args: Array<String>) {
val pair = Pair(1, "one")
val (num, name) = pair
println("num = $num, name = $name")
}

class Pair<K, V>(val first: K, val second: V) {
operator fun component1(): K {
return first
}

operator fun component2(): V {
return second
}
}

data class User(val name: String, val id: Int)

fun getUser(): User {
renturn User("Alex", 1)
}

fun main(args: Array<String>) {
val user = getUser()
println("name = ${user.name}, id = ${user.id}")

//or
val (name, id) = getUser()
println("name = $name, id = $id")

//or
println("name = ${getUser().compont1()}, id = ${getUser().componet2()}")
}

fun main(args: Array<String>) {
val map = hashMapof<String, Int>()
map.put("one", 1)
map.put("two", 2)

for ((key, value) in map) {
println("key = ${key}, value = $value")
}
}

data class User(val name: String, val id: Int)

fun main(args: Array<String>) {
val user = User("Alex", 1)
println(user) // toString

val secondUser = User("Alex", 1)
val thirdUser = User("Max", 2)

println("user == seconedUser: ${user == secondUser}")//true
println("user == thirdUser: ${user == thirdUser}")//false

//copy() function
println(user.copy())
println(user.copy("Max"))
println(user.copy(id = 2))
println(user.copy("Max", 2))
}

class Example {
var p: String by Delegate()

override fun toString() = "Example Class"
}

class Delegate() {
operator fun getValue(thisRef: Any?, prop: KProperty<*>): String {
return "$thisRef, thank you for delegating '${prop.name}' to me!"
}

operator fun setValue(thisRef: Any?, prop: KProperty<*>, value: String) {
println("$value has been assigned to ${prop.name} in $thisRef")
}
}

fun main(args: Array<String>) {
val e = Example()
println(e.p)
e.p = "NEW"
}

// 后续调用 get() 只是返回记录的结果。
class LazySample {
val lazy: String by lazy {
println("computed!")
"my lazy"
}
}

fun main(args Array<String>) {
val sample = LazySample()
println("lazy = ${sample.lazy}")
println("lazy = ${sample.lazy}")
}

/*Delegates.observable() 接受两个参数：初始值和修改时处理程序（handler）。 每当我们给属性赋值时会调用该处理程序（在赋值后执行）。它有三个参数：被赋值的属性、旧值和新值：*/
class User {
var name: String by Delegates.observable("no name") {
prop, old, new ->
println("$old -> $new")
}
}

fun main(args Array<String>) {
var user = User()
user.name = "Carl"
}

class User {
var name: String by Delegates.notNull()
fun init(name: String) {
this.name = name
}
}

fun main(args: Array<String>) {
val user = User();
//user.name -> IllegalStateException
user.init("Carl")
println(user.name)
}

class User(val map: Map<String, Any?>) {
val name: String by map
val age: Int by map
}

fun main(args: Array<String>) {
val user = User(mapOf(
"name" to "John doe",
"age" to 25
))
println("name = ${user.name}, age = ${user.age}")
}

/*"Callable References" or "Feature Literals", i.e. an ability to pass
* named functions or properties as values. Users often ask
* "I have a foo() function, how do I pass it as an argument?".
* The answer is: "you prefix it with a `::`".*/
fun main(args: Array<String>) {
val numbers = listOf(1, 2, 3)
println(numbers.filter(::isOdd))
}

fun isOdd(x: Int) = x % 2 != 0