CODEWITHSUNDEEP
scalaoverridingscala-java-interop
Vinicius Carvalho
Vinicius Carvalho

Reputation: 4156

Scala: Overriding methods from java interface

I'm trying to implement a generic java interface in scala. I have looked at: How do I extend Java interface containing generic methods in Scala? And Scala: Overriding Generic Java Methods II

But still I could not find an answer. Here's the method signature from Spring web:

T read(Class<? extends T> clazz, HttpInputMessage inputMessage)
            throws IOException, HttpMessageNotReadableException;

I tried the following in scala:

 @throws(classOf[IOException])
  @throws(classOf[HttpMessageNotReadableException])
  override def read[T](clazz : Class[_ <: T], inputMessage : HttpInputMessage) : T ={
  }

But I get an error saying that this method overrides nothing. If I erase the type by doing:

override def read(clazz : Class[_], inputMessage : HttpInputMessage) : AnyRef ={

It marks the method as being overwritten. My question is how can I keep type safety here and force it to override the interface method?

Regards

EDIT

The spring interface:

public interface HttpMessageConverter<T> {

T read(Class<? extends T> clazz,
       HttpInputMessage inputMessage)
       throws IOException,
              HttpMessageNotReadableException
}

Upvotes: 1

Views: 2397

Answers (2)

oxbow_lakes
oxbow_lakes

Reputation: 134330

I think the problem is likely to be that you have added a type parameter to the read method, rather than using the type parameter from your class declaration:

class MyImpl[T] extends JavaInterface[T] {

  override def read(clazz: Class[_ <: T], ... )

}

If we rename your T to U it becomes clearer what you have done:

class MyImpl[T] extends JavaInterface[T] {

  /** U is not T */
  override def read[U](clazz: Class[_ <: U], ... )

}

You might also try and sing "U is not T" to the tune of REM's Losing My Religion to hammer the point home.

Upvotes: 8

Sergey Passichenko
Sergey Passichenko

Reputation: 6930

In java you have parameterilized interface, but in scala you try to parameterize method.

Upvotes: 0

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