Which of the following Java code fragments compiles and executes without error? : Questions « Type Casting « SCJP

1. SCJP
2. Type Casting
3. Questions

import java.util.Observable;
import java.util.Observer;

class ApBase implements Runnable {
  public void run() {
  }
}

class ApDerived extends ApBase implements Observer {

  public void update(Observable o, Object arg) {
    // TODO Auto-generated method stub
    
  }

}

  ApBase aBase = new ApBase() ;
  ApDerived aDer = new ApDerived();



   A. Object obj = aBase ;
      Runnable rn = obj ;

   B. Object obj = aBase ;
      Runnable rn = (Runnable) obj ;

   C. Object obj = aBase ;
      Observer ob = (Observer)aBase ;

   D. Object obj = aDer ;
      Observer ob2 = obj ;