Chapter 4 - Using Classes and Objects

Question 1

An object’s data items are also known as .

a) fields

b) functions

c) themes

d) instances

Answer 1

A fields

Question 2

You send messages or information to an object through its .

a) fields

b) methods

c) classes

d) type

Answer 2

methods

When you use an object and its methods, think of being able to send a message to the object to direct it to accomplish some task—you can tell the Party object named myGraduationParty to set the date and time you request. Even though yourAnniversaryParty is also a member of the Party class, and even though it also has access to setDate() and setTime() methods, the arguments you send to yourAnniversaryParty methods will be different from those you send to myGraduationParty methods. Within any object-oriented program, you are continuously making requests to objects’ methods and often including arguments to send information as part of those requests.

Question 3

A program or class that instantiates objects of another prewritten class is a(n) .

a) class client

b) superclass

c) object

d) patron

Answer 3

A class client

You can call an application or class that instantiates objects of another class a class client or a class user . Understanding classes and how objects are instantiated from them is the heart of object-oriented thinking.

Question 4

The body of a class is always written .

a) in a single line, as the first statement in a class

b) within parentheses

c) between curly braces

d) as a method call

Answer 4

C between curly braces

Question 5

Most class data fields are .

a) private

b) public

c) static

d) final

Answer 5

A private

You already have learned that the access specifier for most Java methods is public. However, most fields, such as empNum in the Employee class, are private, which provides the highest level of security. Assigning private access to a field means that no other classes can access the field’s values, and only methods of the same class are allowed to set, get, or otherwise use private variables. The principle used in creating private access is sometimes called information hiding and is an important component of object-oriented programs. A class’s private data can be changed or manipulated only by a class’s own methods and not by methods that belong to other classes.

Question 6

The concept of allowing a class’s private data to be changed only by a class’s own methods is known as .

a) structured logic

b) object orientation

c) information hiding

d) data masking

Answer 6

C information hiding

the object-oriented programming principle used when creating private access for data fields that describes that a class’s private data can be changed or manipulated only by a class’s own methods.

Question 7

Suppose you declare an object as Book myJournal;. Before you store data in myJournal, you .

a) also must explicitly allocate memory for it

b) need not explicitly allocate memory for it

c) must explicitly allocate memory for it only if it has a constructor

d) cannot explicitly declare memory for it

Answer 7

A also must explicitly allocate memory for it

When you declare an integer as int someValue;, you notify the compiler that an integer named someValue will exist, and you reserve computer memory for it at the same time. When you declare the someEmployee instance of the Employee class, you are notifying the compiler that you will use the identifier someEmployee. However, you are not yet setting aside computer memory in which the Employee named someEmployee might be stored—that is done automatically only for primitive type variables. To allocate the needed memory for an object, you must use the new operator .

Question 8

If a class is named Student, the class constructor name is .

a) any legal Java identifier

b) any legal Java identifier that begins with S

c) StudentConstructor()

d) Student()

Answer 8

D Student()

Whether you write your own constructor or use the one automatically created by Java, the name of the constructor is always the same as the name of the class whose objects it constructs.

Question 9

If you use the automatically supplied default constructor when you create an object, .

a) int fields are set to 0 (zero)

b) char fields are set to blank

c) boolean fields are set to true

d) String fields are set to blanks

Answer 9

A int fields are set to 0 (zero)

When the prewritten, default constructor for the Employee class is called, it establishes one Employee object with the identifier provided. The automatically supplied default constructor provides the following specific initial values to an object’s data fields:

Numeric fields are set to 0 (zero).

Character fields are set to Unicode '\u0000'.

Boolean fields are set to false.

Fields that are object references (for example, String fields) are set to null (or empty).

Question 10

If you declare a variable as an instance variable within a class, and you declare and use the same variable name within a method of the class, then within the method, .

a) the variable used inside the method takes precedence

b) the class instance variable takes precedence

c) the two variables refer to a single memory address

d) an error will occur

Answer 10

A the variable used inside the method takes precedence

this refers to the ‘this’ reference; Usually, you neither want nor need to refer to the ‘this’ reference within the instance methods that you write, but the this reference is always there, working behind the scenes so that the data field for the correct object can be accessed

Question 11

A constructor parameters.

a) can receive

b) cannot receive

c) must receive

d) can receive a maximum of 10

Answer 11

A can receive parameters

a class contains constructors that are invoked to create objects from the class blueprint; constructor declarations look like method declarations – except that they use the name of the class and have no return type; You don’t have to provide any constructors for your class, but you must be careful when doing this. The compiler automatically provides a no-argument, default constructor for any class without constructors. This default constructor will call the no-argument constructor of the superclass.

Question 12

A constructor overloaded.

a) must be

b) cannot be

c) can be

d) is always automatically

Answer 12

C can be

as long as the parameter lists and data types are different then you can overload a constructor; it is similar to overloading a method

Question 13

Usually, you want each instantiation of a class to have its own copy of .

a) the data fields but not the methods

b) the methods but not the data fields

c) both the data fields and the methods

d) neither the data fields nor the methods

Answer 13

A the data fields but not the methods

Question 14

If you create a class that contains one method, and you instantiate two objects, you usually store for use with the objects.

a) one copy of the method

b) two copies of the method

c) two different methods containing two different this references

d) data only (the methods are not stored)

Answer 14

A one copy of the method

Question 15

The this reference .

a) can be used implicitly

b) must be used implicitly

c) must not be used implicitly

d) must not be used

Answer 15

A can be used implicitly

Question 16

Methods that you reference with individual objects are .

a) private

b) public

c) static

d) nonstatic

Answer 16

D nonstatic

if you are creating a class from which objects will be instantiated, most methods probably will be nonstatic because you will associate the methods with individual objects. For example, the getEmpNum() method must be nonstatic because it returns a different empNum value for every Employee object you ever create. Nonstatic methods , those methods used with object instantiations, are called instance methods . You can use either a static or nonstatic method with an object, but only nonstatic methods behave uniquely for each object. You cannot use a nonstatic method without an object.

Question 17

Variables that are shared by every instantiation of a class are .

a) class variables

b) private variables

c) public variables

d) illegal

Answer 17

A class variables

class variables are typically private because you only want the methods associated with the class to be able to manipulate the data within the class (class variable)

Question 18

The keyword final used with a variable declaration indicates .

a) the end of the program

b) it is in a static method

c) a symbolic constant

d) that no more variables will be declared in the program

Answer 18

C a symbolic constant

the reserved word ‘final’ used in a variable declaration means that the variable cannot be altered

Question 19

Which of the following statements determines the square root of a number and assigns it to the variable s?

a) s = sqrt(number);

b) s = Math.sqrt(number);

c) number = sqrt(s);

d) number = Math.sqrt(s);

Answer 19

B s = Math.sqrt(number);

s is the variable name and number is the value that will be assigned to the variable ‘s’

Question 20

Which of the following expressions correctly returns an integer that represents the month of a LocalDate object named hireDate?

a) getMonth(hireDate)

b) getMonthValue(hireDate)

c) hireDate.getMonthValue()

d) hireDate.setMonthValue()

Answer 20

C hiredate.getMonthValue()