Kotlin class implementing Java interface error

Question

I've got a Java interface

public interface SampleInterface extends Serializable {
    Long getId();
    void setId(Long id);
}

and a Kotlin class that is supposed to implement it

open class ClazzImpl() : SampleInterface

private val id: Unit? = null

fun getId(): Long? {
    return null
}

fun setId(id: Long?) {

}

However I get a compilation error:

Class ClazzImpl is not abstract and does not implement abstract member public abstract fun setId(id: Long!): Unit defined in com....SampleInterface

any ideas what is wrong?

Bob · Accepted Answer · 2017-08-22 06:48:09Z

8

The other answers from Egor and tynn are important, but the error you have mentioned in the question is not related to their answers.

You have to add curly braces first.

open class ClazzImpl() : SampleInterface {

  private val id: Unit? = null

  fun getId(): Long? {
    return null
  }

  fun setId(id: Long?) {

  } 

}

If you add the curly braces, that error would have gone but you will get a new error like this:

'getId' hides member of supertype 'SampleInterface' and needs 'override' modifier

Now, as suggested in the other answers, you have to add override modifier to the functions:

open class ClazzImpl() : SampleInterface {

      private val id: Unit? = null

      override fun getId(): Long? {
        return null
      }

      override fun setId(id: Long?) {

      } 

}

edited Aug 22, 2017 at 6:48

answered Aug 21, 2017 at 17:13

Bob

13.9k7 gold badges38 silver badges45 bronze badges

Sign up to request clarification or add additional context in comments.

Comments

Egor Neliuba · Accepted Answer · 2017-08-21 15:21:26Z

4

You have to add the override keyword before fun:

override fun getId(): Long? {
    return null
}

override fun setId(id: Long?) {
}

answered Aug 21, 2017 at 15:21

Egor Neliuba

15.1k7 gold badges62 silver badges81 bronze badges

1 Comment

Mena Over a year ago

Looks like the docs are pretty explicit indeed: "[...]we stick to making things explicit in Kotlin. And unlike Java, Kotlin requires explicit annotations for overridable members (we call them open) and for overrides[...]"

tynn · Accepted Answer · 2017-08-22 09:51:16Z

2

When you implement an interface within Kotlin, you have to make sure to override the interface methods inside of the class body:

open class ClazzImpl() : SampleInterface {

    private var id: Long? = null

    override fun getId(): Long? {
        return id
    }

    override fun setId(id: Long?) {
        this.id = id
    }
}

edited Aug 22, 2017 at 9:51

answered Aug 21, 2017 at 15:48

tynn

40k8 gold badges119 silver badges152 bronze badges

Collectives™ on Stack Overflow

Kotlin class implementing Java interface error

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

3 Answers 3

Comments

1 Comment

Comments

Your Answer

Sign up or log in

Post as a guest

Related