Mock PA 1

Snatch!

Topic Coverage

Abstract Classes / Interfaces
Inheritance vs Composition
Design Principles

Problem Description

Snatch is yet another transport service provider trying to vie for a place in the public transport arena.

Snatch provides three types of ride services: JustRide, TakeACab and ShareARide.

There are also different types of drivers under Snatch. Each can provide a subset of the services above.

A customer can issue a Snatch ride request, specified by the distance of the ride, the number of passengers, and the time of the request.

Task

You shall be given a request, followed by a list of NormalCab or PrivateCar drivers together with their corresponding waiting times.

The task is to provide a list of bookings in order of increasing fares by matching the drivers and the services they provide to the given request.

Break ties among the same lowest fares by selecting the booking with the smaller waiting time.

Take note!

There are altogether five levels. You are required to complete ALL levels.

You should keep to the constructs and programming discipline instilled throughout the module.

Write each class/interface in its own file.
Ensure that ALL object properties and class constants are declared private final.
Ensure that that your classes are NOT cyclic dependent.
Use only java libraries taught in class.
You are NOT allowed to use java keywords/literals: null, instanceof (except within the typical equals method)
You are NOT allowed to use Java reflection, i.e. Object::getClasses and other methods from java.lang.Class
You are NOT allowed to use * wildcard imports.
You are NOT allowed to define array constructs, e.g. String[] or using ellipsis, e.g. String…

You may assume that all tests provide valid arguments to methods; hence there is no need to validate method arguments.

In the following level specifications, you will be guided on the classes and non-private methods to define. DO NOT create any other classes. Moreover, any other method you create must be declared private.

Level 1

The fare of a service is based upon the distance travelled, the number of passengers, and the time of the service.

JustRide is one such service:

Fare is based on the distance @ 22 cents per km
Fare is the same regardless of the number of passengers (pax)
There is no booking fee.
A surcharge of 500 cents if a ride request is issued between the peak hour of 600 hrs to 900 hrs, both inclusive

Create the JustRide service with computeFare method the takes in three integer arguments comprising the distance, number of passengers, and time of service. The method returns the fare in cents.

$ja v a cyo u r_{j} a v a_{f} i l es$ jshell your_java_files_in_bottom-up_dependency_order jshell> new JustRide() $.. ⇒ JustRide

jshell> new JustRide().computeFare(20, 3, 1000) $.. ⇒ 440

jshell> new JustRide().computeFare(10, 1, 900) $.. ⇒ 720

jshell> new JustRide() instanceof Service $.. ⇒ true

Note that Service is an interface.

Level 2

Define a Request class that encapsulates the distance, number of passengers, and time. Write a method computeFare that takes in a service and returns the fare accordingly.

$ja v a cyo u r_{j} a v a_{f} i l es$ jshell your_java_files_in_bottom-up_dependency_order jshell> new Request(20, 3, 1000) $.. ⇒ 20km for 3pax @ 1000hrs

jshell> new Request(20, 3, 1000).computeFare(new JustRide()) $.. ⇒ 440

jshell> new Request(10, 1, 900) $.. ⇒ 10km for 1pax @ 900hrs

jshell> new Request(10, 1, 900).computeFare(new JustRide()) $.. ⇒ 720

In addition, include the TakeACab service:

Fare is based on the distance @ 33 cents per km, but there is a booking fee of 200 cents
Fare is the same regardless of the number of passengers (pax)
No peak hour surcharge

jshell> new TakeACab() $.. ⇒ TakeACab

jshell> new Request(20, 3, 1000).computeFare(new TakeACab()) $.. ⇒ 860

jshell> new Request(10, 1, 900).computeFare(new TakeACab()) $.. ⇒ 530

jshell> new TakeACab() instanceof Service $.. ⇒ true

Level 3

Now, include a NormalCab driver who is identified by its license plate number (a string) and the passenger waiting time in minutes. NormalCab drivers provide JustRide and TakeACab services.

Include the rankBestServices that takes in a request, and rank its services according to increasing fares.

$ja v a cyo u r_{j} a v a_{f} i l es$ jshell your_java_files_in_bottom-up_dependency_order

jshell> new NormalCab(“SHA1234”, 5) $.. ⇒ SHA1234 (5 mins away) NormalCab

jshell> new NormalCab(“SHA1234”, 5) instanceof Driver $.. ⇒ true

jshell> new NormalCab(“SHA1234”, 5).rankBestServices(new Request(20, 3, 1000)) instanceof Stream $.. ⇒ true

jshell> new NormalCab(“SHA1234”, 5).rankBestServices(new Request(20, 3, 1000)). …> toList() $.. ⇒ [Pair[t=JustRide, u=440], Pair[t=TakeACab, u=860]]

Now add a Booking class that takes in a driver and a request. From the services that a driver provides, the best service with the lowest fare is selected.

To compare two bookings using their computed fare, we let the Booking class implement the Comparable interface that specifies a compareTo method to be implemented. (note that this is different from the Comparator interface).

class Booking implements Comparable { … @Override public int compareTo(Booking other) { … } }

Note that if both fares are the same, we prefer the one with the shorter waiting time.

$ja v a cyo u r_{j} a v a_{f} i l es$ jshell your_java_files_in_bottom-up_dependency_order jshell> new NormalCab(“SHA1234”, 5) $.. ⇒ SHA1234 (5 mins away) NormalCab

jshell> new Booking(new NormalCab(“SHA1234”, 5), new Request(20, 3, 1000)) .. ⇒ $4.40 using SHA1234 (5 mins away) NormalCab (JustRide)

jshell> new NormalCab(“SHA2345”, 10) $.. ⇒ SHA2345 (10 mins away) NormalCab

jshell> new Booking(new NormalCab(“SHA2345”, 10), new Request(10, 1, 900)) .. ⇒ $5.30 using SHA2345 (10 mins away) NormalCab (TakeACab)

jshell> Booking b1 = new Booking(new NormalCab(“SHA2345”, 10), new Request(10, 1, 900)) b1 ⇒ $5.30 using SHA2345 (10 mins away) NormalCab (TakeACab)

jshell> Booking b2 = new Booking(new NormalCab(“SHA2345”, 10), new Request(10, 1, 900)) b2 ⇒ $5.30 using SHA2345 (10 mins away) NormalCab (TakeACab)

jshell> Comparable cmp = b1 cmp ⇒ $5.30 using SHA2345 (10 mins away) NormalCab (TakeACab)

jshell> b1.compareTo(b2) 0 $.. > true

jshell> Booking b3 = new Booking(new NormalCab(“SHA1234”, 5), new Request(10, 1, 900)) b3 ⇒ $5.30 using SHA1234 (5 mins away) NormalCab (TakeACab)

jshell> Booking b4 = new Booking(new NormalCab(“SHA2345”, 10), new Request(10, 1, 900)) b4 ⇒ $5.30 using SHA2345 (10 mins away) NormalCab (TakeACab)

jshell> b3.compareTo(b4) < 0 $.. ⇒ true

Level 4

Now include the ShareARide service:

Fare is based on the distance @ 50 cents per km
A surcharge of 500 cents if a ride request is issued between 600 hrs to 900 hrs, both inclusive
There is no booking fee
The total fare is divided equally among the number of passengers
Any fractional part of the fare is absorbed by your friendly driver

Moreover, include

PrivateCar drivers that provide JustRide and ShareARide services.

You should aim to make the Booking class general such that it does not need to check for any invalid pairing, say between PrivateCar driver and TakeACab service. If you have designed your program appropriately, then extending your program with additional drivers and services would not require any modification to existing classes.

$ja v a cyo u r_{j} a v a_{f} i l es$ jshell your_java_files_in_bottom-up_dependency_order jshell> new ShareARide() $.. ⇒ ShareARide

jshell> new PrivateCar(“SMA7890”, 5) $.. ⇒ SMA7890 (5 mins away) PrivateCar

jshell> new PrivateCar(“SMA7890”, 5).rankBestServices(new Request(20, 3, 1000)).toList() $.. ⇒ [Pair[t=ShareARide, u=333], Pair[t=JustRide, u=440]]

jshell> new Booking(new PrivateCar(“SMA7890”, 5), new Request(20, 3, 1000)) .. ⇒ $3.33 using SMA7890 (5 mins away) PrivateCar (ShareARide)

jshell> new PrivateCar(“SLA5678”, 10) $.. ⇒ SLA5678 (10 mins away) PrivateCar

jshell> new Booking(new PrivateCar(“SLA5678”, 10), new Request(10, 1, 900)) .. ⇒ $7.20 using SLA5678 (10 mins away) PrivateCar (JustRide)

jshell> Booking b1 = new Booking(new PrivateCar(“SMA7890”, 5), new Request(10, 1, 900)) b1 ⇒ $7.20 using SMA7890 (5 mins away) PrivateCar (JustRide)

jshell> Booking b2 = new Booking(new PrivateCar(“SLA5678”, 10), new Request(10, 1, 900)) b2 ⇒ $7.20 using SLA5678 (10 mins away) PrivateCar (JustRide)

jshell> b1.compareTo(b2) < 0 $.. ⇒ true

Level 5

Now complete the task by defining the findBestBooking method in Main.java that returns the list of booking matches sorted by increasing fare (breaking ties by waiting time).

You may assume that no two bookings have the same fare and the same waiting time.

jshell> /open Main.java

jshell> findBestBooking(new Request(20, 3, 1000), …> List.of(new NormalCab(“SHA1234”, 5), new PrivateCar(“SMA7890”, 10))). …> forEach(booking → System.out.println(booking)) $3.33 u s in g SM A 7890 (10 min s a w a y) P r i v a t e C a r (S ha re A R i d e)$ 4.40 using SHA1234 (5 mins away) NormalCab (JustRide)

jshell> findBestBooking(new Request(10, 1, 900), …> List.of(new NormalCab(“SHA1234”, 5), new PrivateCar(“SMA7890”, 10))). …> findFirst() $.. ==> Opt i o na l [$ 5.30 using SHA1234 (5 mins away) NormalCab (TakeACab)]

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