Scala: Get value of child from parent? - scala

Question

Trying to get values of all fields of child from parent class like this:
for (field <- this.getClass.getDeclaredFields) {
Logger.debug(field.getName)
field.get(this)
}
and got error
Exception: Class models.Model$$anonfun$4 can not access a member of
class models.Good with modifiers "private"
at line
field.get(this)
In Good class I don't have private fields:
class Good(id: Option[String]) extends Model[realGood](id){
lazy val title: String = this.load[String](realObject.get.title)
lazy val cost: Double = this.load[Double](realObject.get.cost)
}
What's wrong with this code?

Answer 1

As hinted in the comments, Scala's conversion to java bytecode isn't always straightforward (though it's usually pretty predictable, once you get the hang of it). In particular, public fields in Scala compile to a private field with a public getter in java bytecode:
fukaeri:~ dlwh$ cat zzz.scala
class Good(id: Option[String]) {
lazy val title: String = ???
lazy val cost: Double = ???
}
fukaeri:~ dlwh$ scalac zzz.scala
fukaeri:~ dlwh$ javap -private Good
Compiled from "zzz.scala"
public class Good {
private java.lang.String title;
private double cost;
private volatile byte bitmap$0;
private java.lang.String title$lzycompute();
private double cost$lzycompute();
public java.lang.String title();
public double cost();
public Good(scala.Option<java.lang.String>);
}
You can see that Good has private fields for each of your declared public fields, in addition to public getters. Because the fields are lazy val, they also have computation methods for initialization, and there's a bitmap$0 field to ensure that the lazy vals are initialized only once.
In your loop, you can use field.setAccessible(true) to fix your exception.