Scala constructor overload?

It's worth explicitly mentioning that Auxiliary Constructors in Scala must either call the primary constructor (as in landon9720's) answer, or another auxiliary constructor from the same class, as their first action. They cannot simply call the superclass's constructor explicitly or implicitly as they can in Java. This ensures that the primary constructor is the sole point of entry to the class.

class Foo(x: Int, y: Int, z: String) {  
  // default y parameter to 0  
  def this(x: Int, z: String) = this(x, 0, z)   
  // default x & y parameters to 0
  // calls previous auxiliary constructor which calls the primary constructor  
  def this(z: String) = this(0, z);   
}

 class Foo(x: Int, y: Int) {
     def this(x: Int) = this(x, 0) // default y parameter to 0
 }

As of Scala 2.8.0 you can also have default values for contructor- and method parameters. Like this

scala> class Foo(x:Int, y:Int = 0, z:Int=0) {                           
     | override def toString() = { "Foo(" + x + ", " + y + ", " + z + ")" }
     | }
defined class Foo

scala> new Foo(1, 2, 3)                                                    
res0: Foo = Foo(1, 2, 3)

scala> new Foo(4)                                                          
res1: Foo = Foo(4, 0, 0)

Parameters with default values must come after the ones with no default values in the parameter list.