bluehenry/kotlin.demo

kotlin cheatsheet

Command line

kotlinc
kotlinc hello.kt -include-runtime -d hello.jar
java -jar hello.jar

Geting start with Kotlin

var vs val

var is a variable val is a value. It is immutable

Decompiler

fernflower

String Templates

Using 'if' as an Expression

val message = if (str == str1 {
    "Correct"
} else {
    "Wrong"
}

Handle null

var str:String? = null
str? = "Give a value"

'hen' statement is similar with 'switch'

when(str) {
    str1 -> print("Correct")
    else -> print("Wrong")
}

'try' statement

val number:Int = try {
    Integer.parseInt(int1)
} catch(e:NumberFormatException) {
    null
}

Looping

for (i in 10 downTo 1 step 2 {
}

var ages = TreeMap<String, Int>()
ages = ["Kevin"] = 25
ages = ["Henry"] = 19
for((name, age) in ages) {

}

Exception

var reader = FileReader("filename") try { reader.read() } catch (e :IOException) {

} finally {

}

Functions in Kotlin

Don't need to be part of a class Are introduced with the 'fun' keyword Can have default parameters Can have named parameters Can 'extend' existing types Support function expressions

fun max(a: Int, b: Int): Int = if(a>b) a else b

Calling from Java

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