Object-Oriented Programming: Classes and Encapsulation

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Questions and Answers

What do instance variables do?

Control program flow

Specify methods of a class

Manage user inputs

Store the data of an object (correct)

What is an instance of a class?

An object of the class

What is an instance variable?

A storage location present in each object of the class

What does the class declaration specify?

The instance variables Signup and view all the answers

What do an object's instance variables store?

The data required for executing its methods Signup and view all the answers

What consists of an instance variable declaration?

Access specifier (private), type of variable (such as int), name of variable (such as value) Signup and view all the answers

You should declare all instance variables as __________.

private Signup and view all the answers

Each object of a class has its own set of instance __________.

variables Signup and view all the answers

What is encapsulation?

The process of hiding implementation details and providing methods for data access Signup and view all the answers

How can you encapsulate data?

Declare instance variables as private and declare public methods that access the variables Signup and view all the answers

What does encapsulation allow programmers to do?

Use a class without having to know its implementation Signup and view all the answers

What is information hiding?

It makes it simpler for the implementor of a class to locate errors and change implementations Signup and view all the answers

What is the purpose of instance variable declarations?

To specify the access level, type, and name of the variable Signup and view all the answers

What is the role of a constructor?

To initialize the instance variables of the object Signup and view all the answers

The name of the __________ is always the same as the name of the class.

constructor Signup and view all the answers

A constructor that takes no arguments is called a __________ constructor.

no-argument Signup and view all the answers

The constructors and methods of a class go __________ the class declaration.

inside Signup and view all the answers

What forms the public interface of a class?

Public constructors and methods of a class Signup and view all the answers

What is javadoc?

A program that automatically generates a set of HTML pages Signup and view all the answers

What are @param tags used for?

Methods that have no arguments Signup and view all the answers

@return tags are used for?

Methods whose return type is void Signup and view all the answers

When commenting, you need to provide comments for?

Every class, every method, every parameter variable, and every return value Signup and view all the answers

How can you empty the harrysChecking bank account using public interface methods?

harrysChecking.withdraw(harrysChecking.getBalance()) Signup and view all the answers

What is wrong with the statement: BankAccount harrysChecking = new BankAccount(10000); System.out.println(harrysChecking.withdraw(500));

The withdraw method has return type void. It doesn't return a value. Signup and view all the answers

How would you change the public interface to accommodate an account number?

Add an accountNumber parameter to the constructors, and add a getAccountNumber method. Signup and view all the answers

Why is the following documentation comment questionable? public int getAccountNumber()

The first sentence of the method description should describe the method—it is displayed in isolation in the summary table. Signup and view all the answers

What does the private implementation of a class consist of?

Instance variables, the bodies of constructors, the bodies of methods Signup and view all the answers

What is the job of a constructor?

To initialize the instance variables of the object Signup and view all the answers

Study Notes

Instance Variables and Classes

Instance variables store the data specific to an object, unique to each instance of a class.
Every object of a class has a separate set of instance variables, ensuring data encapsulation.
Declaring instance variables as private enhances encapsulation, restricting direct access from outside the class.

Class Declaration

Class declaration defines the instance variables and their types.
A well-defined class includes public methods to manipulate its private instance variables.

Encapsulation

Encapsulation hides the implementation details of a class while providing access through public methods.
Information hiding simplifies error tracing and allows for easier modifications within the class.

Method Behavior

Methods such as public void unclick() can manipulate instance variables to ensure class functionality.
To access private instance variables (like hours and minutes in a Clock class), invoke public methods.

Constructor Basics

Constructors initialize instance variables when an object is created; a no-argument constructor sets default values (e.g., zero).
The constructor’s name matches the class name, serving as an entry point for object instantiation.

Public Interface

The public interface of a class consists of public constructors and method declarations.
Proper documentation (javadoc) is essential for methods to clarify their purpose, parameters, and return values.

Bank Account Example

In designing a BankAccount class, interactions occur through public methods, e.g., harrysChecking.withdraw(harrysChecking.getBalance()).
Enhancements to the class can include additional parameters (like account number) to enrich its representation without frequent updates.

Documentation Best Practices

Documentation comments should accurately describe methods and constructors, ensuring users understand their functionalities.
Misleading or vague comments can cause confusion about method purposes and expected behavior.

Implementation Details

The private implementation of a class includes instance variables and method bodies, which are shielded from external access.
Constructors play a crucial role in setting initial values for instance variables, maintaining the integrity of the object state.

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Description

This quiz focuses on the fundamentals of instance variables, class declaration, and encapsulation in object-oriented programming. It covers how instance variables are utilized within classes and the importance of data encapsulation for maintaining class integrity. Test your understanding of methods and their role in manipulating instance variables.