How to extend a class that has multiple constructors in Kotlin?

Question

I am in the processing of learning Kotlin and ran into a problem I couldn't figure out. I would like to extend the Java class RuntimeException in Kotlin and be able to use any one of three of its constructors, in different circumstances (based on what info I have at the time I want to throw an exception). In java my class would look like this:

public class PhotoLibException extends RuntimeException {      public PhotoLibException(String message, RuntimeException ex) {         super(message, ex);     }      public PhotoLibException(String message) {         super(message);     }      public PhotoLibException(RuntimeException ex) {         super(ex);     } } 

When I try to do this in Kotlin, I used this answer as a guide: Kotlin secondary constructor however, I had a problem trying to figure out how to invoke the appropriate super constructor correctly. For example, using functions seemed to be a good approach, like this:

fun PhotoLibException(message: String): PhotoLibException {     val ex = null     return PhotoLibException(message, ex) }  fun PhotoLibException(ex: Exception): PhotoLibException {     val message = ""     return PhotoLibException(message, ex) }  class PhotoLibException(message: String, ex: Exception?): RuntimeException(message, ex) { } 

However, in this Kotlin example above, I am always invoking the super constructor with two args, and not invoking the constructor most appropriate to the situation. So what I have above works, but doesn't do exactly what it would do in Java where a different constructor is invoked in each situation. I also tried instantiating a new RuntimeException inside each fun above and casting it to PhotoLibException, but I wasn't allowed to do that.

Can anyone suggest how I would do this correctly in Kotlin?

Answer 1

Update: Since M11 (0.11.*), you can use secondary constructors to solve this problem:

class PhotoLibException : RuntimeException {     constructor(message: String, ex: Exception?): super(message, ex) {}     constructor(message: String): super(message) {}     constructor(ex: Exception): super(ex) {} } 

Currently, there's no way to call different super-constructors in different context from the same class. It will be supported in the upcoming months, though.

Answer 2

Use the @JvmOverloads annotation.

class PhotoLibException: RuntimeException {    @JvmOverloads constructor(message: String, ex: Exception?) }