CSCI Quiz 7

What are the differences between Polymorphism and Inheritance in Java?

-Inheritance 'represents the parent-child relationship' between two classes. -Polymorphism 'take the advantage of that relationship' to make the program more dynamic. -Inheritance helps in code reusability in child class 'by inheriting behaviour from parents class'. -Polymorphism enables child class 'to redefine already defined behaviour inside parent class'.

What is Polymorphism in Java OOPs?

-Polymorphism means "many forms" in Greek. That is one thing that can take many forms. -Polymorphism is a concept by which we can perform a single task in different ways. -When a single entity (object) behaves differently in different cases, it is called polymorphism. -In other words, if a single object shows multiple forms or multiple behaviors, it is called polymorphism.

Consider a class hierarchy that includes a class called Vehicle, with subclasses called Car and Airplane. The Vehicle class has a method called getMaxSpeed(), which is overridden in the Car class. The getMaxSpeed() of the Vehicle class returns 760 mph, while the getMaxSpeed() method of the Car class is overridden to return 150 mph. What is the output of the following snippet of code? Vehicle v = new Car(); System.out.println(v.getMaxSpeed() + " mph");

150

Consider the following inheritance hierarchy that is used in a video game: Character / \ Friend Villain / \ / \ WiseMan ShopKeeper Dragon Skeleton | | FlyingDragon EliteSkeleton

Character c = new FlyingDragon( ); Villann v = new Skeleton( );

An interface cannot declare any instance variables.

False

Polymorphism via inheritance requires that all classes in the inheritance hierarchy are concrete.

False

Consider a reference declared in the following manner. Animal a; This reference may only point to an object that created by instantiating the Animal class.

False Could also point to sub-classes

Suppose Animal is an interface that specifies a single method - speak. Now suppose the Dog class implements the Animal interface. In addition to the speak method, the Dog class also has a method called wagTail. Now consider the following code. Animal a = new Dog(); a.wagTail(); Which of the following is true about this code? -It will result in a compile-time error. -It will result in a run-time error. -It will call the speak method defined in the Animal interface. -It will call the wagTail method defined in the Dog class.

It will result in a compile-time error.

You need to create a reference variable that can refer to objects from many different classes. You do not know the inheritance hierarchies of the classes. The safest class to use to declare the reference variable is ________

Object

What is the output of the below program if no errors? class A { void m1(Object obj){ System.out.println("One"); } }class B extends A { void m1(Object obj){ super.m1(null); System.out.println("Two"); } void m2(Object obj){ System.out.println("Three"); this.m1(null); } }public class Test{ public static void main(String[] args){ A a = new B(); a.m1(new A()); B b = new B(); b.m2(new B()); } }

One Two Three One Two

What are the types of Polymorphism in Java?

Static polymorphism Dynamic polymorphism Compile time polymorphism Runtime polymorphism

Let Dog be a subclass of Animal, and suppose Animal has a method called speak( ) that is overridden in the Dog class. Consider the following code. Animal spot = new Dog( ); spot.speak( ); Which of the following is true? -This code will result in a run-time error. -The speak method defined in the Animal class will be called. -The speak method defined in the Dog class will be called. -The speak method will not be called at all.

The speak method defined in the Dog class will be called.

A parameter to a method can be polymorphic

True

An interface name may be used as a reference type.

True

Compile-time binding is more efficient than dynamic binding.

True

In Java, polymorphic method binding occurs __________.

at run time

The commitment to execute certain code to carry out a method invocation is referred to as ________.

binding

In Java, polymorphic references can be created through the use of _________ and _________.

inheritance, interfaces

Which one is dynamic binding in Java?

method overriding

A polymorphic reference is one that can refer to _______ type(s) of object(s).

multiple