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println("b = $b ${b.javaClass}")
println("f1 = $f1 ${f1.javaClass}")
println("boolean1 = $boolean1 ${boolean1.javaClass}")
println("str = $str ${str.javaClass}")


b = 127 byte
f1 = 3.14 float
boolean1 = true boolean
str = ABC class java.lang.String


package my

val familyName = "Hong"
var givenName: String = "GilDong"

fun printMyName() {
    println("My name is '$givenName $familyName`")
}

fun main() {
    givenName = "Alice" //재할당 reassign var
		// familyName = "Kim" //Error - Val cannot be reassigned
    printMyName()
}


fun main() {
    val favNumber: Int = 7
    var myAge = 7
		println("favNumber = ${favNumber.inc()}")
		println("myAge = ${myAge.inc()}")
		
		println("favNumber = ${favNumber}")
		println("myAge = ${myAge}")
}


favNumber = 8
myAge = 8
favNumber = 7
myAge = 7


b.javaClass = byte -128 ~ 127
s.javaClass = short -32768 ~ 32767
i.javaClass = int -2147483648 ~ 2147483647
l.javaClass = long -9223372036854775808 ~ 9223372036854775807

f.javaClass = float 1.4E-45 ~ 3.4028235E38
d.javaClass = long 4.9E-324 ~ 1.7976931348623157E308


package kotlin

public open class Any {

		public open operator fun equals(other: Any?): Boolean
		
		public open fun hashCode(): Int
		
		public open fun toString(): String
}

kotlin.Any


package main

fun main() {
    //kotlin.Any 최상위 타입 클래스
    
    val a1 : Any = 1234
    val a2 : Any = 'A'
    
    var a3 : Any = "xyz"
    a3 = 3.141592
    a3 = true
}


package main

fun main() {
    val b1 = 365
    println(b1 is Int) // 타입 체킹 is 
}


package main

fun main() {

    val c: Byte = 127
    val c2 : Any = c

    val d: Byte = c2 as Byte
		val d2: Int = c2 as Int// ClassCastException
}


package main


fun whichType(data: Any){
    if(data is String) {
		println("data.length = ${data.length}")
		    }else if(data is Int){
		println("data*2 = ${data*2}")
		    }else{
		println("$data 는 ${data.javaClass} 형이다.")
		        val result = data as? Float
		println("float 라면? data = $result")
    }
}

fun main() {
whichType(1);
whichType("hi")
whichType(1.0F)
whichType(true)
}

실행 결과 :
---
data*2 = 2
data.length = 2
1.0 는 class java.lang.Float 형이다.
float 라면? data = 1.0
true 는 class java.lang.Boolean 형이다.
float 라면? data = null


fun main() {
    var a: String = "ABCD" //non-null type
//    a = null //Null can not be a value of a non-null type String
    
    var b: String? = "XYZ" //nullable type
//    b = null //null 저장 가능

    println("a.length = ${a.length}")
//    println("b.length = ${b.length}")
//    Only safe (?.) or non-null asserted (!!.) calls are allowed on a nullable receiver of type String?

	println(b?.length) //safe call                  -> null
	println(b!!.length) //non-null asserted call    -> KotlinNullPointException

	println("b의 길이 => ${
        if(b!=null) b.length
        else "b는 null임!"
    }")
	println("b의 길이 => ${b?.length ?: "b는 null임!"}")
}

Section 2. Data Types, Variable, Null Safety

Data Types

Variable vs. Constant

Numbers

Char & String

Base/Radix

`Any`

`is` 연산자

캐스팅

Nullable

Section 2. Data Types, Variable, Null Safety

Data Types

Variable vs. Constant

Numbers

Char & String

Base/Radix

Any

is 연산자

캐스팅

Nullable

`Any`

`is` 연산자