Kotlin val初始化时使用

Question

Using Java I may want to initialize a final variable using a switch statement:

final String finalValue;

switch (condition) {
   case 1:
      finalValue = "One";
      break;
   case 2:
      finalValue = "Two";
      break;
   case 3:
      finalValue = "Three";
      break;
   default:
      finalValue = "Undefined";
      break;
}

In Kotlin, trying to do the same:

val finalValue: String

when (condition) {
   1 -> finalValue = "One"
   2 -> finalValue = "Two"
   3 -> finalValue = "Three"
   else -> finalValue = "Undefined"
}

result in a compilation error.
A solutions is using the by lazy combination, but this create a new Lazy instance.

val finalValue: String by lazy {    
   when (condition) {
      1 -> "One"
      2 -> "Two"
      3 -> "Three"
      else -> "Undefined"
   }
}

Is there a better way to accomplish this?

Answer 1

How about this construction:

    val finalValue: String = when (condition) {
        1 -> "One"
        2 -> "Two"
        3 -> "Three"
        else -> "Undefined"
    }

Using when as an expression.

Answer 2

You can also use init block to initialize a final variable.

val finalValue: String

init {
    finalValue = when (condition) {
        1 -> "One"
        2 -> "Two"
        3 -> "Three"
        else -> "Undefined"
    }
}

Answer 3

Actually, the following does compile, I'm not sure which problem you encountered?

fun x(condition: Int = 5) {
    val finalValue: String

    when (condition) {
        1 -> finalValue = "One"
        2 -> finalValue = "Two"
        3 -> finalValue = "Three"
        else -> finalValue = "Undefined"
    }
}

The only possibility to me: You wrote the when clause into a class body directly, which certainly does not work. You could put it into an init block though.

But of course it's much nicer to simply use the power of when expression here (Which the IDE also suggests):

val finalValue = when (condition) {
    1 -> "One"
    2 -> "Two"
    3 -> "Three"
    else -> "Undefined"
}