Kotlin Null Safe Example

NullSafe.kt

// Kotlin null safe example
// Java null risk example https://gist.github.com/gaplo917/5dc037bedea39a348854ae59ba89c063

fun doSth(str: String): String {
    return str.toLowerCase()
}

fun doSthOptional(str: String?): String? {
    // Optional chainning, similiar to Swift
    return str?.toLowerCase()
}

doSth(null) // compile error
doSth("Abc") // return "abc"

doSthOptional(null) // return null
doSthOptional("Abc") // return "abc"

// More example on copmile-time checking
var a0 // fail, compile error  
var a1 = null // fail, compile error  
var a2: String = null // fail, compile error  
var a3: String? = null // OK

println(a3) // OK, print null  
println(a3.toLowerCase()) // fail, compile error  
println(a3?.toLowerCase()) // OK, print null