[Kotlin] Control Flow - if/when/loops

if

fun test() {

val a = 10

val b = 20

var max = a

if ( a < b ) max = b

}

if else

fun test() {

val a = 10

val b = 20

val max = if ( a > b ) a else b

}

fun test() {

val a = 10

val b = 20

val max : Int

if ( a > b ) {

max = a

} else {

max = b

}

}

fun test() {

val a = 10

val b = 20

val max : Int

val min : Int

if ( a > b ) {

max = a

min = b

} else {

max = b

min = a

}

}

println("max $max min $min")

java switch

int a = 10;

switch (a) {

case 1 : 

case 10 :

// ...

break;

default : 

// ...

break;

}

When

-> Kotlin

val a = 10

when (a) {

1, 10 -> // ...

else -> // ...

}

val validNumbers = 9..10

val a : Any = 30

when(a) {

in 1..10 -> println("1~10")

in validNumbers -> println("validNumbers")

!in 10..20 -> println("a is outside the range")

else -> println("else")

}

-> in : 포함, !in : 포함하지 않은 경우

fun printString(a : Any) {

when (a) {

1, 10 -> println("1~10")

is String -> println(a)

else -> println("else")

}

}

isString("message")

-> is : instanceof

When return

fun isString(a : Any) = when (a) {

is String -> true

else -> false

}

println(isString("message"))

printSample(SampleOne("taehwan"))

printSample(SampleTwo(20))

fun printSample(sample : Sample) {

when (sample) {

is SampleOne -> println("sample name : ${sample.name}")

is SampleTwo -> println("sample age : ${sample.age}")

}

}

// -> 다음과 같은 data class 정의

sealed class Sample

data class SampleOne(val name : String) : Sample()

data class SampleTwo(val age : Int) : Sample()

For - java

String name = "name";

for (int i = 0; i < name.length(); i++) {

name.charAt(i);

}

List<String> list = new ArrayList<>();

list.add("name");

list.add("bbb");

for (String s : list) {

System.out.println(s);

}

For - kotlin

val name = "name"

for (i in name) {

println("i $i")

}

val list = mutableListOf(1, 2, 3, 4, 5)

for (i in list) {

println("i $i")

}

For - list에서 index가 필요하면

val list = mutableListOf(1, 2, 3, 4, 5)

for (i in list.indices) {

println("i ${list[i]}")

}

-> indices를 사용

For - list에서 index와 value가 모두 필요하면

val list = mutableListOf(1, 2, 3, 4, 5)

for ((index, value) in list.withIndex()) {

println("$index $value")

}

For - break

val list = mutableListOf(1, 2, 3, 4, 5)

for ((index, value) in list.withIndex()) {

println("$index $value")

if(index == 1) {

break

}

}

For - step

-> java

for (int i = 0; i < 10; i+=2) {

System.out.println("value " + i);

}

-> kotlin

for (value in 1..10 step 2) {

println("value $value")

}

For - map

val map = mutableMapOf(1 to "ABC", 2 to "BBB", 3 to "CCC")

for ((key, value) in map) {

println ("key $key value $value")

}

For - map - Decompile

Map map = MapsKt.mutableMapOf(new Pair[] {

TuplesKt.to(Integer.valueOf(1), "ABC"),

TuplesKt.to(Integer.valueOf(2), "BBB"),

TuplesKt.to(Integer.valueOf(3), "CCC")});

Iterator var3 = map.entrySet().iterator();

while(var3.hasNext()) {

Entry var2 = (Entry) var3.next();

int key = ((Number)var2.getKey()).intValue();

String value = (String)var2.getValue();

String var6 = "key " + key + " value "+ value;

System.out.println(var6);

}