Qz12
Which statement best describes the relationship between base class and derived class types?
A derived class reference can be assigned to a base class variable, but a base class reference cannot be assigned to a derived class variable.
Consider the abstract class below: public abstract class Foo { private int a; public int b; public Foo( int aVal, int bVal ) { a = aVal; b = bVal; } // end Foo constructor public abstract int calculate(); } // end class Foo Any concrete subclass that extends class Foo:
All of the above
Select the best true statement
Both B and C are correct statements.
T/F Attempting to instantiate an object of an abstract class is a logic error.
False
T/F Polymorphism allows the addition of classes providing they were at least considered during program development.
False
T/F When used correctly, Polymorphism will never require changes to be made to any part of the program.
False
T/F You may define implementations for abstract methods to act as default implementations
False
Classes and methods are declared sealed for all of the following reasons, except:
Sealed methods are static
T/F An abstract class may be derived from another abstract class.
True
T/F If a derived class reference is assigned to a base class variable, the variable must be cast back to the derived class before any derived class methods can be called with it.
True
T/F Polymorphism allows you to command a wide variety of objects even if you do not know the objects' types.
True
T/F Polymorphism enables objects of different classes that are related by a class hierarchy to be processed generically
True
T/F Sealing methods allows the compiler to optimize the program by "inlining code."
True
T/F The abstract methods and properties of a class do not provide an implementation
True
T/F an abstract base class can be used to declare references
True
If a method needs to be called polymorphically, what type of reference should be used to point to the object that the method is being called with?
a reference of the base class that defines the behavior of the object
Polymorphism specifically enables the creation of programs that handle:
a wide variety of classes in a general manner
Assigning a derived class reference to a base class variable is safe:
because the derived class is an object of its base class.
Polymorphism allows for specifics to be dealt with during:
execution
A(n) ____ is best used for providing services that bring together objects of otherwise unrelated classes.
interface
Declaring a method sealed means:
it cannot be overridden
The keyword sealed is applied to methods and classes to:
prevent overriding and inheritance
Polymorphism enables you to:
program in the general.
The purpose of an interface is to:
provide different types of objects with the comparable functionality, even though each will implement the functionality differently
Which declaration declares abstract method method 1 in abstract class Class1 (method 1 returns an int and takes no arguments)?
public abstract int method1();