Leon's Lengthy Learner Lab

• Objective - to implement a ZipCodeWilmington class which mediates a composite Students and Instructors singleton reference.
• Purpose - to demonstrate the use of
  • interfaces
  • abstract classes
  • concrete classes
  • enums
  • generics

Part 1.1 - Create Person Class

• Create a Person class.
  • The class should declare a final field named id of type long.
  • The class should declare a field named name of type String.
  • Person constructor should have a parameter of type long and String which sets the id and name field to the respective values.
  • The class should define a getId() method which returns the Person object's id field.
  • The class should define a getName() method which returns the Person object's name field.
  • The class should define a setName() method which sets the Person object's name field.

Part 1.0 - Test Person

• Create a TestPerson class.
  • Create a testConstructor method which ensures that a Person object's id and name field are being set upon construction.
  • Create a testSetName method which ensures that a Person object's name variable is being set by invoking the .setName method.

Part 2.0 - Create Learner Interface

• Create a Learner interface.
  • Learner should declare method signature:
    • Method name: learn
    • Method parameters: double numberOfHours
    • Method return-type: void
  • Learner should declare method signature:
    • Method name: getTotalStudyTime
    • Method return-type: Double

Part 3.1 - Create Student Class

• Create a Student class such that:
  • Student is a subclass of Person
  • Student implements the Learner interface
  • Student should have an instance variable totalStudyTime of type double
  • Student should have a concrete implementation of the learn method which increments the totalStudyTime variable by the specified numberOfHours argument.
  • Student should have a getTotalStudyTime() method which returns the totalStudyTime instance variable.

Part 3.0 - Test Student

• Create a TestStudent class.
  • Create a testImplementation method that asserts that a Student is an instanceof a Learner.
  • Create a testInheritance method that asserts that a Student is an instanceof a Person.
  • Create a testLearn method that ensures a Student's totalStudyTime instance variable is incremented by the specified numberOfHours by invoking the .learn method.

Part 4.0 - Create Teacher Interface

• Create a Teacher interface.

  • Teacher should declare a teach method signature:

    • Method name: teach
    • Method parameters:
      • Learner learner
      • double numberOfHours
    • Method return-type: void

  • Teacher should declare a lecture method signature:

    • Method name: lecture
    • Method parameters:
      • Learner[] learners
      • double numberOfHours
    • Method return-type: void

Part 5.1 - Create Instructor Class

• Create an Instructor class such that:
  • Instructor is a subclass of Person
  • Instructor implements the Teacher interface
  • Instructor should have a concrete implementation of the teach method which invokes the learn method on the specified Learner object.
  • Instructor should have a concrete implementation of the lecture method which invokes the learn method on each of the elements in the specified array of Learner objects.
    • numberOfHours should be evenly split amongst the learners.
      • double numberOfHoursPerLearner = numberOfHours / learners.length;

Part 5.0 - Test Instructor

• Create a TestInstructor class.
  • Create a testImplementation method that asserts that an Instructor is an instanceof a Teacher.
  • Create a testInheritance method that asserts that a Instructor is an instanceof a Person.
  • Create a testTeach method that ensures when an Instructor invokes the teach method, a respective student's totalStudyTime instance variable is incremented by the specified numberOfHours.
  • Create a testLecture method that ensures when an Instructor invokes the lecture method, a respective array of students' totalStudyTime instance variables is incremented by numberOfHours/students.length.

Part 6.1 - Create People class

• Create a People class.
  • The class should instantiate a List field of Person objects named personList.
  • The class should define a method named add which adds a Person to the personList.
  • The class should define a method named findById which makes use of a long id parameter to return a Person object with the respective id field.
  • The class should define a named contains which makes use of a Person person parameter to return true if the personList contains the respective Person object.
  • The class should define a method named remove which makes use of a Person person parameter to remove a respective Person object.
  • The class should define a method named remove which makes use of a long id parameter to remove a Person object with the respective id field.
  • The class should define a named removeAll which clears our personList field.
  • The class should define a method named count which returns the size of personList.
  • The class should define a method named toArray which returns an array representation of the personList field.
  • The class should implement Iterable<E> and define a method named iterator which makes use of the personList field to generate a new a Iterator<E>.

Part 6.0 - Test People

• Create a TestPeople class.
  • Create a testAdd method which ensures that our personList in our People class populated with respective Person objects following invokation of the add method.
  • Create a testRemove method which ensures that the personList in a People object is depopulated with a respective Person object following the invokation of the remove method.
  • Create a testFindById method which ensures that a respective Person object with a respective id field is returned upon invokation of the findById method on a respective People object.

Part 7.1 - Create Students singleton

• Note: The creation of this class will demonstrate an implementation of singleton design pattern.
• Create a Students class.
  • The class should be an unextendable subclass of the People class.
  • The class should statically instantiate a final field named INSTANCE of type Students.
  • The class should define a private nullary constructor which populates the INSTANCE field with respective Student representations of your colleagues.
    • Each student should have a relatively unique id field.
  • The class should define a getInstance method which returns the INSTANCE field.

Part 7.0 - Test Students singleton

• Create a TestStudents class.
  • Create a test method which ensures that each of the students in your current cohort are in your Students singleton.

Part 8.0 - Create and Test Instructors singleton

• Use Part 7 as a reference.
• Create a Instructors singleton which represents the set of instructors at ZipCodeWilmington.
• Create a TestInstructors class.

Part 9.1 - Create ZipCodeWilmington Class

• Create a ZipCodeWilmington singleton.
  • The class should declare a field that references the instance of Students called students.
  • The class should declare a field that references the instance of Instructors called instructors.
  • The class should define a method hostLecture which makes use of a Teacher teacher, double numberOfHours parameter to host a lecture to the composite personList field in the students reference.
  • The class should define a method hostLecture which makes use of a long id, double numberOfHours parameter to identify a respective Instructor to host a lecture to the composite personList field in the students reference.
  • The class should define a method getStudyMap which returns a new instance of a mapping from Student objects to Double objects, representative of each respective student's totalStudyTime.

Part 9.0 - Test ZipCodeWilmington

• Create a TestZipCodeWilmington class.
  • Create a testHostLecture method which ensures that each of the Student's totalStudyTime instance variable is incremented by the specified numberOfHours upon invoking the hostLecture method.

Notice the Design Flaw - Odd Casting Issues

• You may have noticed that the findById, and hostLecture methods require an intermediate casting trick.
• To remedy this issue, we can generify the People class.

Part 10.1 - Modify People class

• Parameterize the People signature to enforce that it is a container for objects of type E such that E is a subclass of Person.
• Modify the class signature to declare this class abstract.
  • An abstract class cannot be instantiated; Its concrete implementation is deferred to its subclass.
• Modify people field to enforce that is a container of objects of type E.
• Modify the add method to ensure that it handles object of type E.
• Modify the findById method to ensure that it returns an object of type E.
• Modify the getArray method signature by declaring it abstract of return tyoe E.
  • An abstract method is a subclass's contractual agreement to the deferment of an implementation of a respective method.

Part 10.2 - Modify People subclasses

• Modify the Students class signature to ensure that it is a subclass of People of parameterized type Student.
• Modify the Instructors class signature to ensure that it is a subclass of People of parameterized type Instructor.
• Provide concrete implementations of the getArray method in each of these classes.

Part 10.3 - Refactor ZipCodeWilmington class

• Refactor the hostLecture method in the ZipCodeWilmington class by removing any intermediate casting trick(s).

Part 10.0 - Test refactored classes.

• Ensure that the TestStudents, TestInstructors, TestPeople, TestZipCodeWilmington classes were not affected by the refactor.

Notice the Design Flaw - Non-Intuitive Orientation

• You may have noticed that findById makes it difficult to intuitively identify which Person object is being returned. To remedy this issue, we can make use of an enum which manipulates a composite instructor object.

Part 11.1 - Create Educator enum

• Create an enum named Educator.
  • The enum should implement Teacher.
  • The enum should have an enumeration for each of the instructors represented in the Instructors class.
  • Upon construction each enumeration of the enum should instantiate a respective Instructor and assign it to a final instructor field upon construction. The instructor should be added to the Instructors singleton.
  • Calls to the teach and lecture method should be deferred to the composite instructor reference.
  • The enum should have a double timeWorked field which keeps track of the hours that the Educator has taught.

Part 11.0 - Test Educator

• Use Part 5 as a reference.

Part 12.0 - Test ZipCodeWilmington

• Ensure the hostLecture method can handle objects of type Educator.