class Employee(name: String,age:Int,college:String?,var company:String):Student(name,age,college){
    override fun isEligibleToVote():Boolean{
        return  true
    }
    fun Person.isTeenager():Boolean{
        return  age in 13..19
    }
    fun isOctogenarian(): Boolean = age in 13..19
    val sumLambda: (Int,Int)->Int = {x,y -> x+y}

    fun doubleTheResult(x: Int, y: Int, f:(Int,Int)-> Int): Int{
        return f(x,y)*2
    }
    fun Test(){
        var result: Int = doubleTheResult(4,5,sumLambda)
        var r1 = 1..5
        var r2 = 1 downTo 5
        //如果步长不是1，则需要使用step函数，例如：
        var r3 = 1 downTo 5 step 2  //5 3 1

        var age  = 12;
        var isEligibleToVote = if(age>11) "yes" else "no"

        var typeOfPerson = when(age){
            0 -> "New born"
            in 1..12 -> "Child"
            in 13..19 -> "Teenager"
            else ->     "Adult"

        }

        //遍历一个String对象数组
        val names =  arrayOf("Jake", "Jill", "Ashley", "Bill")
        for(name in names){
            println(name)
        }

        //Kotlin允许在字符串中嵌入变量和表达式，例如：
        val name = "Bob"
        println("My name is $name")

        var a = 100
        var b = 200
        println("The sum is ${a+b}")
    }

创建 Javabean 对象 关键字：data

data class Customer(val name: String, val email: String)

包含以下所有的属性：

• getters (and setters in case of vars) for all properties

• equals()
• hashCode()
• toString()
• copy()
• component1(), component2(), …, for all properties (see Data classes)

过滤list集合

val positives = list.filter { x -> x > 0 } 
or
val positives = list.filter { it > 0 }

字符串拼接：

println("Name $name") 
and
println("Name ${a+b}")

Instance Checks

when (x) {
    is Foo -> ...
    is Bar -> ...
    else   -> ...
}

Traversing a map/list of pairs

for ((k, v) in map) {
    println("$k -> $v")
}

Using ranges

for (i in 1..100) { ... }  // closed range: includes 100
for (i in 1 until 100) { ... } // half-open range: does not include 100
for (x in 2..10 step 2) { ... }
for (x in 10 downTo 1) { ... }
if (x in 1..10) { ... }

Read-only list

val list = listOf("a", "b", "c")

Read-only map

val map = mapOf("a" to 1, "b" to 2, "c" to 3)

Accessing a map

println(map["key"])
map["key"] = value

Creating a singleton:object

object Resource {
    val name = "Name"
}

If not null shorthand

val files = File("Test").listFiles()

println(files?.size)

If not null and else shorthand

val files = File("Test").listFiles()

println(files?.size ?: "empty")

Executing a statement if null

val data = ...
val email = data["email"] ?: throw IllegalStateException("Email is missing!")

Execute if not null

val data = ...

data?.let {
    ... // execute this block if not null
}

Return on when statement

fun transform(color: String): Int {
    return when (color) {
        "Red" -> 0
        "Green" -> 1
        "Blue" -> 2
        else -> throw IllegalArgumentException("Invalid color param value")
    }
}

'try/catch' expression

fun test() {
    val result = try {
        count()
    } catch (e: ArithmeticException) {
        throw IllegalStateException(e)
    }

    // Working with result
}

'if' expression

fun foo(param: Int) {
    val result = if (param == 1) {
        "one"
    } else if (param == 2) {
        "two"
    } else {
        "three"
    }
}

Calling multiple methods on an object instance ('with')

class Turtle {
    fun penDown()
    fun penUp()
    fun turn(degrees: Double)
    fun forward(pixels: Double)
}

val myTurtle = Turtle()
with(myTurtle) { //draw a 100 pix square
    penDown()
    for(i in 1..4) {
        forward(100.0)
        turn(90.0)
    }
    penUp()
}

Java 7's try with resources

val stream = Files.newInputStream(Paths.get("/some/file.txt"))
stream.buffered().reader().use { reader ->
    println(reader.readText())
}