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Exam 10: Inheritance and Polymorphism

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Question 21

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An abstract class ____.

A) does not have any subclasses
B) is a superclass with many subclasses
C) cannot be instantiated
D) is the base class of all other classes

E) C) and D)
F) A) and D)

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Question 22

Multiple Choice

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Which operator is used to determine if an object is of a particular class type?

A) The operator new
B) The dot (.) operator
C) The instanceof operator
D) The + operator

E) A) and B)
F) None of the above

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Question 23

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In Java, you can automatically make a reference variable of a subclass type point to an object of its superclass.

Redefining a method of a superclass is also known as overloading a method.

In dynamic binding, the method that gets executed is determined at compile time, not at execution time.

An interface is a class that contains only abstract methods and/or named constants.

Which of the following statements about the reference super is true?

Suppose there are three classes named Shape, Circle, and Square. What is the most likely relationship between them?

Inheritance implies an "is-a" relationship.

Java uses late binding for methods that are private but not for methods that are marked final.

A polymorphic reference variable can refer to either an object of its own class or an object of the subclasses inherited from its class.

Consider the following class definitions. public class BClass {private int x; public void set(int a) { x = a; } public void print() { }} public class DClass extends BClass {private int y; public void set(int a, int b) {//Postcondition: x = a; y = b;} public void print() { }} Which of the following is the correct definition of the method set of the class DClass? (i) public void set(int a, int b) {super.set(a) ; y = b;} (ii) public void set(int a, int b) {x = a; y = b;}

-Based on the diagram in the accompanying figure, the method setDimension in the class Box ____ the method setDimension in the class Rectangle.

Inheritance is an example of what type of relationship?

Composition is also called ____.

A subclass cannot directly access public members of a superclass.

-Based on the diagram in the accompanying figure, the method area in the class Box ____ the method area in the class Rectangle.

Suppose that the class Mystery is derived from the class Secret. Consider the following statements. Secret secRef = new Secret() ; Mystery mysRef = new Mystery() ; Which of the following statements is legal in Java? (i) secRef = mysRef; (ii) mysRef = secRef;

Consider the following class definitions. public class BClass {private int x; private double y; public void print() { }} public class DClass extends BClass {private int a; private int b; public void print() { }} Suppose that you have the following statement. DClass dObject = new DClass() ; How many instance variables does dObject have?

An abstract method ____.