Polymorphism - Objective Exercises

Which of the following statements is an advantage of polymorphism?

• The same program logic can be used with objects of several related classes.
• Variables can be re-used in order to save memory.
• Constructing new objects from old objects of a similar class saves time.
• Polymorphism is a dangerous aspect of inheritance and should be avoided.

The following key words are normally found in the inheritance and polymorphism concepts EXCEPT

• instanceof
• abstract
• extends
• private

Why is the class member, studentName declared private? (Choose the best answer.)

• So that no classes outside of Student can interfere and use the studentName attribute
• Because all class members are required to be declared private.
• Because it facilitates record keeping.
• Because the programmer wishes to protect the program against hackers wanting to steal vital information.

Which of the following statements is TRUE?

• Polymorphism and inheritance is essentially the same thing.
• Polymorphism means that the method executed in response to a given message will vary according to the class to which the object belongs.
• The instance of operator tests whether an object exist.
• Polymorphism uses array of subclasses.

What is the purpose of defining multiple constructors?

• Multiple constructors are easier to write than a single constructor.
• The Java constructors are easier to write than a single constructor.
• Multiple constructors give the client more flexibility in creating instances.
• Programs with multiple constructors are easier to read than a single constructor.

What is the output of running the class c?

• AB
• BA
• AA
• BB

Which of the following statements about the reference super written in a child class is TRUE?

• It must be used every time method from the superclass is called.
• It must be the last statement of the constructor.
• It must be the first statement of the constructor.
• It can only be used once in a program.

Which of the following statement is TRUE?

• Objects cannot be instantiated from concrete class and abstract class.
• Abstract and concrete classes can have or inherited any abstract methods from the superclass.
• Concrete class can have concrete methods and abstract methods which will be defined in the subclass.
• If the subclass does not override the abstract methods from the superclass, the subclass must be declared as abstract.

What will happen if a class is declared as an abstract class?

• All the derived classes must be declared as abstract class
• All the derived classes must implement the undefined method in the abstract class
• Derived classes cannot redefine the abstract method
• The abstract class can create its own object

Which of the following scenario shows the advantage of polymorphism?

• A function can be given a meaningful name without having to change it to accommodate to rules against having multiple methods of the same name in a single function.
• The extension of a class makes the member variables of the parent available to the class, and saves the time of having to redefine these member variables.
• The introduction of a new class to an already functioning framework of classes using inheritance only requires a user to implement the new class by extending a parent class and adding the appropriate method.
• The extension of a class does not require the programmer to write a method that is defined in the parent. The class instead can call the parent method whenever it wants to.