Object-Oriented Programming

The goal of these exercises is to practise these OOP concepts:

• Classes & Objects
• Inheritance
• Abstraction

For the exercises below, we've provided the starter project above.

📌 Classes & Objects

Part 1

Inside the com.cbfacademy.cars package under the cars module, create a class called Car with the following members:

• private String make
• private String model
• private String colour
• private int year
• public Car(String make, String model, String colour, int year) - constructor that accepts parameters representing the make, model, colour and year of the car
• public String getMake() - returns the car make
• public String getModel() - returns the car model
• public int getYear() - returns the year the car was made
• public String getColour() - returns the colour of the car
• public void setColour() - sets the colour of the car
• public String getDetails() - returns the car details, including the make, model, colour and year

✅ Verify Your Implementation

To verify that your code works as expected, run the CarTest tests.

First, edit object-oriented-programming/cars/pom.xml to uncomment the <testExclude> element:

  <testExclude>**/ShowroomTest.java</testExclude>

ℹ️ Notes

The <testExclude> element excludes the ShowroomTest class from being compiled until you've progressed to the next step, as a compiler error would be thrown otherwise.

In your terminal, ensure that you are in the object-oriented-programming folder, then run the following command:

./mvnw --projects cars clean test -Dtest=CarTest

If you are using the Windows Command Prompt, use mvnw instead of ./mvnw for all commands.

Your implementation is correct when all tests pass.

Part 2

Create a class called Showroom with the following members:

• public List<Car> getCars() - returns a list containing the following three Car objects:
  • a blue Volvo V40 from 2012
  • a red Porsche Panamera from 2009
  • a grey Audi A3 from 2018

In the main method of the App class, instantiate a Showroom object, call getCars() and print the details for each Car instance in the list.

✅ Verify Your Implementation

To verify that your code works as expected, run the ShowroomTest tests.

Edit object-oriented-programming/cars/pom.xml and undo the changes to the <testExclude> element:

  <!-- <testExclude>**/ShowroomTest.java</testExclude> -->

In your terminal, run the following command:

./mvnw --projects cars clean test -Dtest=ShowroomTest

Your implementation is correct when all tests pass.

ℹ️ Notes

If you want to experiment with the provided application in the App.java file, you can run a command in this format ./mvnw -q --projects [project name] clean compile exec:java -Dexec.mainClass=[package].[class] from the terminal:

./mvnw -q --projects cars clean compile exec:java -Dexec.mainClass=com.cbfacademy.cars.App

For any of the later exercises, simply set the appropriate project and package names.

Notice that, unlike the test command, we use the -q flag to suppress the output of the Maven build as we don't need to see the generated informational messages if we're just running our own application code.

📌 Inheritance

Part 1

Inside the com.cbfacademy.accounts package under the accounts module, create a class called Account with the following members:

• public Account(int accountNumber, double balance) - constructor that accepts parameters representing the new account number and starting balance
• public double getBalance() - returns the current account balance
• public int getAccountNumber() - returns the account number
• public double deposit(double amount) - deposits funds to the account and returns the new balance
• public double withdraw(double requested) - withdraws funds from the account and returns the requested amount or 0 if the account has an insufficient balance

ℹ️ Notes

• This account doesn't have an overdraft facility.
• The balance of an account may only be modified through the deposit() and withdraw() methods.
• Consider the necessary instance variables and the appropriate access modifiers to allow any sub-classes to access those values

✅ Verify Your Implementation

To verify that your code works as expected, run the AccountTest tests.

Edit object-oriented-programming/accounts/pom.xml to uncomment the <testExclude> elements:

  <testExclude>**/CurrentAccountTest.java</testExclude>
  <testExclude>**/SavingsAccountTest.java</testExclude>

In your terminal, run the following command:

./mvnw --projects accounts clean test -Dtest=AccountTest

Your implementation is correct when all tests pass.

Part 2

Using the Account class as a base class, create two derived classes:

SavingsAccount with the following members, in addition to the attributes of the Account class:

• public SavingsAccount(int accountNumber, double balance, double interestRate) - constructor that accepts parameters representing the new account number, starting balance and interest rate
• public void applyInterest() applies interest to the account
• public double getInterestRate() - returns the current interest rate
• public void setInterestRate() - sets the interest rate

CurrentAccount with the following members, in addition to the attributes of the Account class:

• public CurrentAccount(int accountNumber, double balance, double overdraftLimit) - constructor that accepts parameters representing the new account number, starting balance and overdraft limit
• public double getOverdraftLimit() - returns the current overdraft limit
• public void setOverdraftLimit() - sets the overdraft limit

ℹ️ Notes

Ensure that you have overridden methods of the Account class where necessary in the derived classes.

✅ Verify Your Implementation

To verify that your code works as expected, run the CurrentAccountTest and SavingsAccountTest tests.

Edit object-oriented-programming/accounts/pom.xml and undo the changes to the <testExclude> elements:

  <!-- <testExclude>**/CurrentAccountTest.java</testExclude> -->
  <!-- <testExclude>**/SavingsAccountTest.java</testExclude> -->

In your terminal, run the following command:

./mvnw --projects accounts clean test -Dtest=CurrentAccountTest,SavingsAccountTest

Your implementation is correct when all tests pass.

🚀 Stretch Goal

If you have extra time in the session, or wish to experiment further, create a Bank class to manage accounts. Consider the following ideas — you may choose to implement some, all or come up with your own:

• storing a internal list of accounts. Remember that accounts in the list could be instances of the Account class, the SavingsAccount class, or the CurrentAccount class.
• opening a new account, given a type and balance.
• getting a list of account numbers held by the bank
• getting an account, given an account number
• closing an account, given an account number
• displaying a report of all accounts held by the bank
• paying a dividend to all accounts held by the bank
• applying interest to all savings accounts
• contacting all current account holders if their account is in overdraft.

Update App.java to create a bank instance and then execute your bank's operations

ℹ️ Notes

There are no tests for the Bank class, so it's up to you how to implement it.

📌 Abstraction

In this exercise you will develop a class hierarchy of shapes and write a program that computes the amount of paint needed to paint different objects. The hierarchy will consist of a parent class Shape with three derived classes - Sphere, Rectangle, and Cylinder.

For the purposes of this exercise, the only attribute a shape will have is a name and the method of interest will be one that computes the area of the shape (surface area in the case of three-dimensional shapes).

Part 1

Inside the com.cbfacademy.shapes package under the shapes module, create an abstract class Shape with the following members:

• abstract double getArea() - returns the area of the shape
• String getName() - returns the name of the shape

In the same package, create a concrete class Sphere that extends Shape:

• Sphere(double radius) - constructor
• double getArea() - overrides the base method. The value is given by the formula (4 * 𝛑 * (radius²))

In the same package, create a concrete class Rectangle that extends Shape:

• Rectangle(double length, double width) - constructor
• double getArea() - overrides the base method. The value is given by the formula (length * width)

In the same package, create a concrete class Cylinder that extends Shape:

• Cylinder(double radius, double height) - constructor
• double getArea() - overrides the base method. The value is given by the formula (height * 𝛑 * (radius²)).

ℹ️ Notes

Consider the appropriate visibility of all constructors, methods and instance variables

✅ Verify Your Implementation

To verify that your code works as expected, run the ShapeTest tests.

Edit object-oriented-programming/shapes/pom.xml to uncomment the <testExclude> element:

  <testExclude>**/PaintTest.java</testExclude>

In your terminal, run the following command:

./mvnw --projects shapes clean test -Dtest=ShapeTest

Your implementation is correct when all tests pass.

Part 2

Inside the shapes package, create a class Paint with the following members:

• Paint(double coverage) - constructor that accepts a parameter representing the number of square feet per gallon this paint can cover
• getAmount(Shape shape) - returns the amount of paint (measured in gallons) needed to paint a given shape

✅ Verify Your Implementation

To verify that your code works as expected, run the PaintTest tests.

Edit object-oriented-programming/shapes/pom.xml and undo the changes to the <testExclude> element:

  <!-- <testExclude>**/PaintTest.java</testExclude> -->

In your terminal, run the following command:

./mvnw --projects shapes clean test -Dtest=PaintTest

Your implementation is correct when all tests pass.

🚀 Stretch Goal

If you have extra time in the session, or wish to experiment further, create a program in the same package that computes the amount of paint needed to paint various shapes, e.g.:

• a rectangular deck of length 35 and width 20
• a ball of radius 15
• a tank of radius 10 and height 30.

Consider the following ideas:

• print the amount of paint needed for each item
• print the overall amount of paint needed to the screen