In Scala, how do I mixin java interfaces into Scala code

Question

For example suppose I have

interface ICar {...}
class Car implements ICar {...}

In Scala I wish to do

new MyScalaClass with ICar

But use the java implementation of ICar i.e. Car. What is the syntax for doing this?

Answer 1

You can use object aggregation, but encapsulating the aggregation in a trait. Suppose you have the following Java code:

interface ICar {
  public void brake();
}
public class Car implements ICar {
  public void brake() { System.out.println("BRAKE !!!"); }
}

Then you can define the following Scala trait:

trait HasCar { self: ICar =>
  private val car = new Car
  def brake() = car.brake()
}

And finally you can mix everything you need into your class:

 val c = new MyScalaClass extends ICar with HasCar
 c.brake // prints "BRAKE !!!"