Wrong output with printf()

Why am I keeping getting 0.0000 in the output ? I've put here some code which is main class, one of the child classes Nuke and parent class -Explosive. I keep getting 0.0000 from the method public void explode() and I guess I'm doing smth wrong with printf(). Could someone help me with that?

Java Code:

public class ExplosiveDemo{

    public static void main(String args[]){

        Explosive frag = new FragGrenade(15.5);

        System.out.println( frag.isRadioactive() ); 
        // false
        frag.explode();
        System.out.println();
        // OUTPUT:
        // Boom: blast radius 15.50 meters

        Explosive nuke = new Nuke(3.2);
        System.out.println(nuke.isRadioactive() ); 
        // true
        nuke.explode();
        // OUTPUT:
        // Boom: blast radius 3200.00 meters
        // Area irradiated
  }

public class Nuke extends Explosive {

    protected double blastAreaKilometers;

    public Nuke(double blastAreaKilometers)
    {
        super(blastAreaKilometers);
    }

    public void explode()
    {
        System.out.printf("Boom: blast radius %f kilometers\n", this.blastAreaKilometers * 1000);
    }
    public boolean isRadioactive()
    {
        return true;
    }

}