Q: What is the maximum number of levels possible in a Multilevel Inheritance in Java?
Solution: There is no limit to the number of levels in a multilevel inheritance chain in Java.
Q: What is the output of the below Java program with Constructors using Inheritance?
class Ant
{
Ant(String name)
{
System.out.print("Inside Ant(String) Constructor. ");
}
}
class WildAnt extends Ant
{
WildAnt()
{
System.out.print("Inside WildAnt() Constructor. ");
}
}
public class Inheritance3
{
public static void main(String[] args)
{
WildAnt wa = new WildAnt();
}
}Solution: Compiler throws an error "implicit constructor of Ant class is undefined". Once you define a Constructor with some arguments, the compiler does not add a default constructor with zero arguments. To subclass a class, defining a default constructor is mandatory.
Q: If a class is not subclassed by any class, then defining a default constructor is not mandatory in Java. State TRUE or FALSE.
Solution: True.
Q: What is the output of the below Java program?
final class Bus
{
void show()
{
System.out.print("Generic Bus. ");
}
}
class ElectricBus extends Bus
{
void show()
{
System.out.println("Electric Bus. ");
}
}
public class Inheritance4
{
public static void main(String[] args)
{
ElectricBus eb = new ElectricBus();
eb.show();
}
}Solution: Notice the use of the keyword "final" before the superclass BUS. You can not subclass a class that is marked final.
Q: A Superclass reference can refer to a Subclass Object without casting. State TRUE or FALSE.
Solution: Yes.
Q: A superclass reference can not be used to invoke a method or variable of the subclass. State TRUE or FALSE.
Solution: Yes. A superclass reference knows only about the methods and properties of the same class but not the subclass.
Q: A subclass object can be used to invoke (call) a method or property of the superclass. State TRUE or FALSE.
Solution: Yes, True.
Q: What is the output of the below Java program on the references of Superclass and Subclass?
class Food
{
void show()
{
System.out.print("FOOD ");
}
}
class Bread extends Food
{
void toast()
{
System.out.print("TOASTED ");
}
}
public class Inheritance5
{
public static void main(String[] args)
{
Food foo = new Food();
foo.show();
Food foo2 = new Bread();
foo2.show();
Bread br = new Bread();
br.toast();
br.show();
}
}Solution: You can only invoke methods of the Superclass using a Superclass reference variable pointing to a Subclass object.
Q: What is the output of the below Java program using Inheritance?
class Furniture
{
void show()
{
System.out.println("Made of Wood. ");
}
}
class Sofa extends Furniture
{
void addCushion()
{
System.out.println("Added. ");
}
}
public class Inheritance6
{
public static void main(String[] args)
{
Furniture fur = new Sofa();
fur.addCushion();
}
}Solution: Yes. The compiler throws an error saying "The method addCushion() is undefined for the type Furniture". It means that you can not call a method of subclass using a superclass reference even though it is pointing to a subclass object.
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