Traits can be implemented and extended on the fly with initialized values. This includes JAVA Interfaces.....

scala trait implementation

trait Similarity {
  def isSimilar(x: Any): Boolean
  def isNotSimilar(x: Any): Boolean = !isSimilar(x)
}

val b = 25

val foo = new Similarity() {
  var x: Int = b
  def isSimilar(x: Any): Boolean = {
    true
  }
}

foo.x
// 25