Derived class mystery

[sandromani]

Okay so here is a tricky example from my lecture notes:

class Base {
    private int val;
    Base () {
    val = lookup();
    }
    public int lookup() { 
    return 5; 
    }
    public int value() {
    return val;
    }
}
class Derived extends Base {
    private int num=10;
    public int lookup() {
    return num;
    }
}
class Test {
    public static void main( String[] args ) {
    Derived d = new Derived();
    System.out.println(d.value());
    }
}
 

I would expect the program to print out 10, but it actually prints out 0... Can anyone explain that?:D

java -version
java version "1.6.0_18"
OpenJDK Runtime Environment (IcedTea6 1.8) (fedora-41.b18.fc13-x86_64)
OpenJDK 64-Bit Server VM (build 14.0-b16, mixed mode)
 

Thanks!

[Oralloy]

The constructor for Base was executed after the memory was allocated for the object, but before the constructor for Derived was executed .... right?

So why do you expect that num was set to anything other than a random (or perhaps the default value) when the Base constructor runs?

Think about it...

[sandromani]

Mh right, makes sense... Thanks!

[Oralloy]

@sandromani
You're welcome.

BTW, I'm not sure what the JVM specification says about such things. That's the ultimate answer, and it probably states that the behaviour is unspecified.