Examine the code below and identify the issue:

Examine the code below and identify the issue:

class Bird { void fly() { System.out.println("Flying"); } }
class Sparrow extends Bird { void chirp() { System.out.println("Chirp"); } }
public class Test {
  public static void main(String[] args) {
    Bird b = new Bird();
    Sparrow s = (Sparrow) b;
    s.chirp();
  }
}