Topics:
- Basics of Objects
- Type Constraints.
Name: WRITE YOUR NAME HERE
// TEST HELPER
def passed(points: Int) {
require(points >=0)
if (points == 1) print(s"
*** Tests Passed (1 point) ***
")
else print(s"
*** Tests Passed ($points points) ***
")
}Problem 1 (20 points): Objects in Scala
A (12 points)
Consider the class below for an employee record in an organization that has three fields name, eid (employee id) and salary.
1) As given, scala will complain that class employee cannot extend the abstract class People. Add the missing methods to enable the class Employee to properly extend People
2) Write a factory pattern that takes in a formatted string of the form “John Doe,29585,33110” consisting of a string and two numbers, to extract the name and salaries for each employee. You may want to use scala.util.matching.Regex [https://www.scala-lang.org/api/2.9.2/scala/util/matching/Regex.html] If the input fails to match the pattern, an IllegalArgumentException must be thrown
Companion objects are covered in scala book Chapter 4.3. Also lookup here: https://alvinalexander.com/scala/factory-pattern-in-scala-design-patterns
import scala.util.matching.Regex
abstract class People {
/* I need the ability to convert every person to a string */
def toString: String
/* I need the ability to check if two people are the same */
def equals (p: People): Boolean
}
/*
Note that for an employee to be equal to an object of type People, that object
must be an employee with matching eid number
*/
class Employee( val name: String, val eid: Int, var salary: Int) extends People {
??? // YOUR CODE HERE
}
object Employee {
def apply(formattedInput: String): Employee = {
/*
Input format must be
(full name with possible spaces)[optional whitespaces],[optional whitespaces](employee ID number)[optional whitespaces],[optional whitespaces](employee salary)
*/
??? // YOUR CODE HERE
}
}//BEGIN TEST
val e1 = Employee("Jonathan Doe, 12893, 39813")
println(e1.toString)
assert(e1.name == "Jonathan Doe", "Failed")
assert(e1.eid == 12893, "Failed")
assert(e1.salary == 39813, "Failed")
assert(e1.equals(new Employee("whoknows", 12893, 39813)))
passed(4)
//END TEST//BEGIN TEST
try {
val e2 = Employee("Badly Formatted String, 29812, $3102")
assert(false, "Failed, the string is badly formatted but your code is OK with it.")
} catch {
case e => println(s"Expected behavior seen")
}
passed(4)
//END TEST//BEGIN TEST
val e1 = Employee("Janet Maria Catherine Doe , 12894 , 121331")
println(e1.toString)
assert(e1.name == "Janet Maria Catherine Doe", "Failed")
assert(e1.eid == 12894, "Failed")
assert(e1.salary == 121331, "Failed")
assert(e1.equals(new Employee("random", 12894, 121332)))
passed(4)
//END TESTB (8 points)
We wish to add a new class of people to our system. These are “Contractor” with the information associated should involve their name (string), contract ID (Integer) and contract supervisor (Employee).
Write a new class named Contractor whose constructor should take in the name of the person (String), their ID number (Integer) and Supervisor (Employee) and extend from People.
A contractor object is equal to an object p of type People, only if p is actually an instance of contractor, and if their names are the same and they have the same contract ID number.
??? // YOUR CODE HERE//BEGIN TEST
val e1 = Employee("Jonathan Doe, 12893, 39813")
val c1 = new Contractor("John Contract Worker", 12093, e1)
assert( !c1.equals(e1), "Failed")
assert( c1.equals(c1), "Failed")
passed(4)
//END TEST//BEGIN TEST
val e1 = Employee("Jonathan Doe, 12893, 39813")
val e2 = Employee("Jane Doe, 12894, 43814")
val c1 = new Contractor("John Contract Worker", 12093, e2)
val c2 = new Contractor("John Contract Worker", 12093, e1)
assert( c1.equals(c2), "Failed")
passed(4)
//END TESTProblem 2 (25 points): Traits in Scala
For this problem, we have defined two traits: NumberOfLegs that helps us define how many legs a given animal has and WarmBlooded that applies to warm blooded animals.
abstract class Animal
trait NumberOfLegs {
val nLegs: Int
def getNumberOfLegs: Int = nLegs
}
trait WarmBlooded extends Animal {
val bodyTempMaintained: Double
def getBodyTemp: Double = bodyTempMaintained
}A (5 points)
Define a class Human that inherits from Animal and mixes in the traits NumberOfLegs with nLegs = 2 and WarmBlooded with bodyTempMaintained = 98. The class Human must take in a parameter called name of type String and implement a getName method without any parameters.
??? // YOUR CODE HERE//BEGIN TEST
val t1 = new Human("Jane Smith")
assert(t1.getNumberOfLegs == 2, "Your human does not have two legs")
assert(t1.bodyTempMaintained == 98.0, "Your human does not maintain a body temp of 98")
assert(t1.getBodyTemp == 98.0, "Your human's getBodyTemp Function is not working")
assert(t1.getName == "Jane Smith", "Your human's name is not setting correctly")
passed(5)
//END TESTB (5 points)
Define a class named Table that mixes in the trait NumberOfLegs with nLegs = 4.
Note: Table cannot mixin the trait WarmBlooded (make sure you understand why that is as a quick check of concepts).
??? // YOUR CODE HERE//BEGIN TEST
val tbl = new Table()
assert(tbl.getNumberOfLegs == 4, "A Table must have four legs")
passed(5)
//END TESTC (15 points)
Define a class called Menagerie with type parameter T such that
- T must always be a derived type of Animal with the trait NumberOfLegs (In scala you can say
T <: A with Bto indicate that a type parameter T must derive from class A with trait B applied). Menageriehas a list of objects of typeT.- The user must be able to instantiate an object of type Menagerie without providing any class parameters:
new Menagerie[T] - The class Menagerie has the method
addAnimalToMenageriethat adds an object of typeTto menagerie and returns a new Menagerie. - Implement a method
addMultipleAnimalsToMenageriethat adds more than one animal. - Add a method
totalLegs: Intthat sums up how many legs the animals in the menagerie have in total.
Here is the template for your solution below.
class Menagerie[T ..constraints..] ( ..class params..) {
// ... Extra Stuff that you may want to add ...
def addAnimalToMenagerie (a: T) : Menagerie[T] = {
// Implement
}
def addMultipleAnimals(animals: List[T]): Menagerie[T] = {
// Implement
}
def totalLegs:Int = {
// Implement
}
}??? // YOUR CODE HERE//BEGIN TEST SETUP
class Donkey extends Animal with NumberOfLegs with WarmBlooded {
val nLegs:Int = 4
val bodyTempMaintained = 96.0
}
class Lion extends Animal with NumberOfLegs {
val nLegs:Int = 4
}
class Mule extends Donkey
val d1 = new Donkey()
val d2 = new Donkey()
val d3 = new Donkey()
val d4 = new Mule()
//END TEST SETUP//BEGIN TEST
val m1 = new Menagerie[Donkey](Nil)
passed(3)
//END TEST//BEGIN TEST
val m1 = new Menagerie[Donkey](Nil)
val m2 = m1.addAnimalToMenagerie(d1)
val n = m2.totalLegs
assert(n == 4, s"1 quadraped = 4 legs. You have $n legs : are you missing legs? Too many legs?")
passed(6)
//END TEST//BEGIN TEST
val m1 = new Menagerie[Donkey](Nil)
val m2 = m1.addMultipleAnimalsToMenagerie(List(d1, d2, d3, d4))
val n = m2.totalLegs
assert(n == 16, s"4 quadrapeds = 16 legs. You have $n legs : are you missing legs? Too many legs?")
passed(6)
//END TEST
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