Invoking scala classes which extends traits during runtime - scala

Question

I am relatively new to scala so please bear me if I asked silly questions.
I have a requirement where I need to invoke a method run time.
I have a trait which is being extended by two classes
trait Animal {
def walk():DataFrame
}
This is extended by two classes.
class Dog(sparkSession: SparkSession) extends Animal {
def walk():DataFrame = {
.............
}
}
class Cat(sparkSession: SparkSession) extends Animal {
def walk():DataFrame = {
.............
}
}
Now from a config file I will get a list of these class names
Lets say like this
val animals = ["com.xy.Dog","com.xy.Cat"]
I need to invoke these classes and execute walk methods.
Can I do something like this?
animals.forEach{ animalString =>
val animalObject = Class.forName(animalString ).newInstance().asInstanceOf(Animal)
animalObject.walk
}

Answer 1

There are a few issues, let's take them one by one:
To build a list in scala you need to do:
val animals = List("com.xy.Dog", "com.xy.Cat")
The forEach method is actually foreach, so there's a small typo. Finally, when you call the newInstance you should get the appropriate constructor before that, otherwise it will use the default one.
animals.foreach { animalString =>
val animalObject = Class.forName(animalString)
.getConstructor(classOf[DataFrame]) // Get the constructor for a DataFrame argument
.newInstance(dataframe) // Pass the dataframe instance
.asInstanceOf[Animal]
animalObject.walk
}
I've made a couple of small changes to the code for you to see it working. You can run the app to see the output:
class Dog extends Animal {
def walk(): Unit = { println("I'm a dog.") }
}
class Cat extends Animal {
def walk(): Unit = { println("I'm a cat.") }
}
object AnimalTest extends App {
val animals = List("com.xy.Dog", "com.xy.Cat")
animals.foreach { animalString =>
val animalObject = Class.forName(animalString)
.newInstance()
.asInstanceOf[Animal]
animalObject.walk
}
}
Note that I've removed the constructor arguments here to easily build instances. The rest is about the same. I hope this helps you.