Question

How do you understand the class parameter in scala. Will the compiler add implicit field to the class for the class parameter.
Like

    class Rational(n:Int, d:Int){
        val num = n
        val den = d
        override def toString = n + "/" + d
    }

do we have 4 fields in class Rational (n, d, num, den)? If not, how can we access n and d in method toString. What’s the mechanism behind this?

Answer 1

n and d will become private fields unless they are only used in the constructor, in which case they’re optimised away. num and den will also be private fields, but they get public accessors as well.

Try this:

class Test(a: String) {
  println(a)
}

Then compile and run javap -private Test, which shows all classes and members of the class:

public class Test extends java.lang.Object{
    public Test(java.lang.String);
}

Then try with a method that uses that parameter:

class Test(a: String) {
  println(a)
  def printa { println(a) }
}

public class Test extends java.lang.Object{
    private final java.lang.String a;        // <- private field
    public void printa();
    public Test(java.lang.String);
}