Question 1

Are there any differences between extending a class and implementing an interface?

Accepted Answer

Yes. First, extending a class uses the extends keyword, while implementing an interface uses the implements keyword. More importantly, a class can implement multiple interfaces, while it can only extend a single class.

Question 2

Consider the following line of code. Comparable s = new String();
Which of the following statements is true about this line?

Accepted Answer

A)  It will result in a compile-time error. 
B)  It will result in a run-time error. 
C)  It will create a String object pointed to by a Comparable reference. 
D)  Although it is perfectly valid Java, it should be avoided due to confusion. 
E)  none of the above are true 
A)  It will result in a compile-time error. 
B)  It will result in a run-time error. 
C)  It will create a String object pointed to by a Comparable reference. 
D)  Although it is perfectly valid Java, it should be avoided due to confusion. 
E)  none of the above are true C

Question 3

In Java, a(n) ___________________ is a collection of constants and abstract methods.

Accepted Answer

A)  polymorphic reference 
B)  abstract class 
C)  implementation 
D)  interface 
E)  iterator 
A)  polymorphic reference 
B)  abstract class 
C)  implementation 
D)  interface 
E)  iterator D

Question 4

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.

Accepted Answer

A) True 
 B)False

Question 5

Give an example of a class that implements the Comparable interface, and explain how the implementation of the compareTo method determines its return value.

Accepted Answer

The String class implements th

Question 6

In Java, polymorphic method binding occurs ____________________ .

Accepted Answer

A)  at run time 
B)  at compile time 
C)  never 
D)  when a programmer writes the code 
E)  during the testing phase of software development 
A)  at run time 
B)  at compile time 
C)  never 
D)  when a programmer writes the code 
E)  during the testing phase of software development

Question 7

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?

Accepted Answer

A)  It will result in a compile-time error. 
B)  It will result in a run-time error. 
C)  It will call the speak method defined in the Animal interface. 
D)  It will call the wagTail method defined in the Dog class. 
E)  none of the above are true. 
A)  It will result in a compile-time error. 
B)  It will result in a run-time error. 
C)  It will call the speak method defined in the Animal interface. 
D)  It will call the wagTail method defined in the Dog class. 
E)  none of the above are true.

Question 8

The compareTo method of the Comparable interface returns a boolean value.

Accepted Answer

A) True 
 B)False

Question 9

The next method of the Iterator interface returns a reference to the next element in a collection and removes it.

Accepted Answer

A) True 
 B)False

Question 10

Suppose that Horse is a subclass of Animal, and neither class is abstract. Which of the following is an invalid declaration and initialization?

Accepted Answer

A)  Horse h = new Horse(); 
B)  Horse h = new Animal(); 
C)  Animal a = new Animal(); 
D)  Animal a = new Horse(); 
E)  all of the above are valid 
A)  Horse h = new Horse(); 
B)  Horse h = new Animal(); 
C)  Animal a = new Animal(); 
D)  Animal a = new Horse(); 
E)  all of the above are valid

Question 11

Write an interface for a CD player. It should have the standard operations (i.e. play, stop, etc) that usual CD players have.

Accepted Answer

public interface CDPlayer {
pu

Question 12

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? Explain your answer.
Vehicle v = new Car();
System.out.println(v.getMaxSpeed() + " mph");

Accepted Answer

The output of this code will be "150 mph

Question 13

Describe the compareTo method the circumstances under which it returns different values.

Accepted Answer

The compareTo method is specified by the

Question 14

Which of the following methods are included with any object that implements the Iterator interface?

Accepted Answer

A)  next 
B)  hasNext 
C)  toString 
D)  all of the above 
E)  a and b 
A)  next 
B)  hasNext 
C)  toString 
D)  all of the above 
E)  a and b

Question 15

In order to create a class that implements an interface, the __________________ keyword is used.

Accepted Answer

A)  extends 
B)  interfaces 
C)  implements 
D)  finalizes 
E)  abstracts 
A)  extends 
B)  interfaces 
C)  implements 
D)  finalizes 
E)  abstracts

Question 16

Late binding is _______________ than _______________ .

Accepted Answer

A)  more efficient, compile-time binding 
B)  less efficient, compile-time binding 
C)  more efficient, run-time binding 
D)  less efficient, run-time binding 
A)  more efficient, compile-time binding 
B)  less efficient, compile-time binding 
C)  more efficient, run-time binding 
D)  less efficient, run-time binding

Question 17

An interface cannot declare any instance variables.

Accepted Answer

A) True 
 B)False

Question 18

Consider the following inheritance hierarchy that is used in a video game.
 
Which of the following declarations and initializations will not cause a compiler error?
Character c = new FlyingDragon();
FlyingDragon f = new Character();
Dragon d = new Villain();
Villain v = new Skeleton();
Dragon d = new ShopKeeper();

Accepted Answer

The following are valid for th

Question 19

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

Accepted Answer

A)  execution 
B)  binding 
C)  polymorphism 
D)  inheritance 
E)  none of the above 
A)  execution 
B)  binding 
C)  polymorphism 
D)  inheritance 
E)  none of the above

Question 20

Which GUI concepts use polymorphism to establish their relationship?

Accepted Answer

A)  a listener and its associated component 
B)  a radio button and its default selection 
C)  a button and its label 
D)  a slider and its tick marks 
E)  none of the above 
A)  a listener and its associated component 
B)  a radio button and its default selection 
C)  a button and its label 
D)  a slider and its tick marks 
E)  none of the above

Are there any differences between extending a class and implementing an interface?

Consider the following line of code. Comparable s = new String(); Which of the following statements is true about this line?

In Java, a(n) ___________________ is a collection of constants and abstract methods.

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.

Give an example of a class that implements the Comparable interface, and explain how the implementation of the compareTo method determines its return value.

In Java, polymorphic method binding occurs ____________________ .

The compareTo method of the Comparable interface returns a boolean value.

The next method of the Iterator interface returns a reference to the next element in a collection and removes it.

Suppose that Horse is a subclass of Animal, and neither class is abstract. Which of the following is an invalid declaration and initialization?

Write an interface for a CD player. It should have the standard operations (i.e. play, stop, etc) that usual CD players have.

Describe the compareTo method the circumstances under which it returns different values.

Which of the following methods are included with any object that implements the Iterator interface?

In order to create a class that implements an interface, the __________________ keyword is used.

Late binding is _ than _ .

An interface cannot declare any instance variables.

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

Which GUI concepts use polymorphism to establish their relationship?

Introduction

Data and Expressions

Using Classes and Objects

Conditionals and Loops

Writing Classes

Graphical User Interfaces

Arrays

Inheritance

Recursion

Exceptions

Searching and Sorting

Trees

Introduction to Collections and Stacks

Heaps and Priority Queues

Graphs

Filters

Exam 9: Polymorphism

Are there any differences between extending a class and implementing an interface?

Consider the following line of code. Comparable s = new String(); Which of the following statements is true about this line?

In Java, a(n) ___________________ is a collection of constants and abstract methods.

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.

Give an example of a class that implements the Comparable interface, and explain how the implementation of the compareTo method determines its return value.

In Java, polymorphic method binding occurs ____________________ .

The compareTo method of the Comparable interface returns a boolean value.

The next method of the Iterator interface returns a reference to the next element in a collection and removes it.

Suppose that Horse is a subclass of Animal, and neither class is abstract. Which of the following is an invalid declaration and initialization?

Write an interface for a CD player. It should have the standard operations (i.e. play, stop, etc) that usual CD players have.

Describe the compareTo method the circumstances under which it returns different values.

Which of the following methods are included with any object that implements the Iterator interface?

In order to create a class that implements an interface, the __________________ keyword is used.

Late binding is _______________ than _______________ .

An interface cannot declare any instance variables.

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

Which GUI concepts use polymorphism to establish their relationship?

Introduction

Data and Expressions

Using Classes and Objects

Conditionals and Loops

Writing Classes

Graphical User Interfaces

Arrays

Inheritance

Recursion

Exceptions

Searching and Sorting

Trees

Introduction to Collections and Stacks

Heaps and Priority Queues

Graphs

Filters

Late binding is _ than _ .