Class Definitions

Question 1

What is the main characteristic of object instances in a class?

Answer 1

Each object instance will have the same behaviour but different property values or ‘state’.

Question 2

What are the three basic components of a class?

Answer 2

• Properties
• Constructors
• Methods

Question 3

What is the process of creating an object from a class called?

Answer 3

Instantiation

Question 4

Define the term ‘class’ in the context of object-oriented programming.

Answer 4

A class is the model or blueprint from which an object is created.

Question 5

True or False: A class reserves memory space for data.

Answer 5

False

Question 6

What are properties in a class?

Answer 6

Properties store data representing the object’s state.

Question 7

What is the role of constructors in a class?

Answer 7

Constructors allow each object to be initialised when created.

Question 8

What do methods implement in a class?

Answer 8

Methods implement the behaviour of the object.

Question 9

Fill in the blank: An object is an instance of a _______.

Answer 9

[class]

Question 10

List the properties of a TicketMachine class.

Answer 10

• Price
• Balance
• Total

Question 11

What is an accessor method?

Answer 11

An accessor method returns information about the state of the object.

Question 12

What is a mutator method?

Answer 12

A mutator method changes the state of the object by modifying its properties.

Question 13

Describe the purpose of the ‘insertMoney’ method in a TicketMachine.

Answer 13

It updates the current balance by adding the amount of money inserted.

Question 14

What is the default constructor?

Answer 14

A constructor with no parameters that Java automatically provides if none is defined.

Question 15

What happens when a method is invoked?

Answer 15

The flow of control jumps to the method and executes its code.

Question 16

What is the purpose of the ‘printTicket’ method?

Answer 16

It prints a ticket and updates the total collected while resetting the balance.

Question 17

What check does the improved ‘insertMoney’ method perform?

Answer 17

It checks that the customer enters a positive amount of money.

Question 18

What does the improved ‘printTicket’ method check before printing a ticket?

Answer 18

It checks that the balance is greater than or equal to the price.

Question 19

What is instance data?

Answer 19

Instance data refers to the values of the properties that each instance of a class has.

Question 20

Define formal parameters.

Answer 20

Formal parameters are the parameter names used inside a constructor or method.

Question 21

Define actual parameters.

Answer 21

Actual parameters are the values supplied to a constructor or method.

Question 22

What is the significance of the return type in a method?

Answer 22

The return type indicates what type of value the method will return to the caller.

Question 23

What is the purpose of the ‘getPrice’ method?

Answer 23

It returns the price of a ticket.

Question 24

What does the constructor of the TicketMachine class do?

Answer 24

It initializes the properties of the TicketMachine object.

Question 25

What is the main method typically used for in an application class?

Answer 25

To initiate or start the execution of the solution using the objects provided.

Question 26

Why is it better practice to explicitly initialize properties?

Answer 26

To ensure properties have a defined value rather than relying on default values.

Question 27

What does the phrase 'method control flow' refer to?

Answer 27

The sequence of execution that occurs when a method is called.

Question 28

What improvements were suggested for the TicketMachine class?

Answer 28

* Check for sufficient money * Refund excess money * Validate ticket price * Allow cancellation of ticket purchase * Track total money collected * Provide a way to empty the machine

Question 29

What does the improved constructor in the TicketMachine class check?

Answer 29

It checks that the ticket price is greater than or equal to zero.

Question 30

What is a local variable?

Answer 30

A variable declared within a method with a scope limited to that method.

Question 31

What does the refundBalance() method do?

Answer 31

It refunds the current balance and resets the balance to zero.

Question 32

What are formal parameters?

Answer 32

Variables that exist only during the constructor or method call and are defined in the header.

Question 33

Define properties (fields).

Answer 33

Variables declared outside methods that persist throughout the object's lifetime and maintain its state.

Question 34

What are local variables initialized by?

Answer 34

They must be initialized before use and are NOT initialized by default.

Question 35

In the testScope method, what is the error related to localVar2?

Answer 35

localVar2's scope is limited to the block of the if statement.

Question 36

What does the statement 'TicketMachine[] machines = new TicketMachine[3];' create?

Answer 36

An array capable of storing 3 references to TicketMachine objects.

Question 37

How do you create instances of TicketMachine and assign them to an array?

Answer 37

By using the new operator to create each instance and assigning it to an element in the array.

Question 38

What do the elements of an array of objects represent?

Answer 38

References to the actual object instances.

Question 39

Can arrays be used as class properties?

Answer 39

Yes, arrays can be used as class properties.

Question 40

What is the role of a class in the context of objects?

Answer 40

A class represents a concept, while an object is the embodiment of that class.

Question 41

What is the purpose of constructors in a class?

Answer 41

To initialize a new instance of an object.

Question 42

What do accessor methods do?

Answer 42

They return information about an object's state.

Question 43

What do mutator methods do?

Answer 43

They change an object's state.

Question 44

Fill in the blank: An object provides a collection of ______ that we can tell it to perform.

Answer 44

[behaviors]

Question 45

True or False: A class can be used to create multiple objects.

Answer 45

True

Question 46

What must a software designer consider when using arrays and objects?

Answer 46

The organization of data and objects that makes sense for the situation.