Question

I have written a Scala class Sheltie to understand how scopes work in Scala. I wrote an equivalent Java Sheltie class just as a cross-reference. This is where I ran into trouble.

In the body of the Scala Sheltie class, there is a method call to the method called bark and a println statement just after the bark call. An equivalent method call bark() can be placed in the equivalent Java class inside another method, but outside of any method, it understandably complains of Duplicate method bark().

I understand how Java code works, so this behavior (in Java) is not surprising. What perplexes is why Scala behaves the way it does.

What I hope to solve is: Why does Scala allow “calls” in the class body and why it allows one to create another val definition in the if block, when Java does not.

Foo.scala

class Sheltie {
  val barkNum = 10

  def bark() {
    //local barkNum of "bark" method
    val barkNum = 20

     if(true){
       //local "barkNum" of if-block
       val barkNum = 30 //why does Scala not complain of a duplicate local variable, when            Java does in the equivalent program Sheltie.java
       println("Inside if block: No of times Riley barked is " + barkNum)
     }

     println("Outside if block: No of times Riley barked is " + barkNum)
  }

  bark //Why does this work, when you can't do this in Java
  println("Outside bark: No of times Riley barked is " + barkNum)
}

Answer 1

When you say Scala allows calls in the class body, the body is actually the constructor, so this is equivalent to having:

public Sheltie()
{
    bark();
    System.out.println("Outside bark: No of times Riley barked is " + barkNum);
}

in Java.