Identify the problem in this Java code:

Identify the problem in this Java code:

class Animal {
  void sound() {
    System.out.println("Animal sound");
  }
}
class Dog extends Animal {
  void sound(int volume) {
    System.out.println("Bark at volume " + volume);
  }
}
public class Test {
  public static void main(String[] args) {
    Animal a = new Dog();
    a.sound();
  }
}