How to instantiate this JAVA-class

Syntax
1

I have this JAVA-class:

public class PostgreSQLContainer<SELF extends PostgreSQLContainer<SELF>> extends JdbcDatabaseContainer<SELF> {
}

The only way I’m able to instantiate it from Scala is having a dummy-class:

class Fisk extends PostgreSQLContainer[Fisk]
val container = new PostgreSQLContainer[Fisk]("postgres:12.1")

Is the a better way?

2

Doesn’t new PostgreSQLContainer[PostgreSQLContainer] work?

3

Looks right to me. The class is designed to be instantiated in a subclass, not in the base class.

Brian Maso

1 Like
4

If this is related to the TestContainers lib, you should have a look at

It makes using test containers from Scala very convenient, but it might
or might not match your use case.

5

No:

Error:(44, 58) class PostgreSQLContainer takes type parameters
	final val postgreSQLContainer = new PostgreSQLContainer[PostgreSQLContainer]("postgres:12.1")
1 Like
6

Thanks, I’ll have a look

7

In Scala 3 you could do:

object container extends PostgreSQLContainer[container.type]

Which is still more heavyweight than simple instantiation though. But it’s a bit weird to have an F-bounded concrete class.

8

BTW; I had to change the PostgreSQLContainerType to:

class PostgreSQLContainerType[SELF](dockerImageName: String) extends PostgreSQLContainer[PostgreSQLContainerType[SELF]](dockerImageName)

The use-case in JAVA is to allow builder-pattern (having the with*()-methods implemented in abstract super-class), and return the concrete class:

new PostgreSQLContainerType[PostgreSQLContainerType[_]]("postgres:12.1")
		.withDatabaseName("XXX").withUsername("XXX").withPassword("XXX")