Question

In this exercise, we will be refactoring a working program. Code refactoring is a process to improve an existing code in term of its internal structure without changing its external behavior.

In this particular example, we have three classes Course, Student, Instructor in addition to Main. All classes are well documented. Read through them to understand their structure. In brief, Course models a course that has a title, max capacity an instructor and students. Instructor models a course instructor who has a name, id and salary. Student models a student who has a name, id, and credits. The Main class create hypothetical instructor, students and course and calls the method print in each object to format the output (see below).

Hani Javadi, instructor ID: 888777666, salary: 11111.0
--- --- ---
Joe Loop, student ID: 810123456, credits: 10
--- --- ---
Mary Collection, student ID: 811987321, credits: 25
--- --- ---
Ke Method, student ID: 810010101, credits: 0
--- --- ---
MIST 4700 MWF 6am-7am
Instructor: Hani Javadi   Room: Z101
Class list:
Joe Loop, student ID: 810123456, credits: 10
Mary Collection, student ID: 811987321, credits: 25
Ke Method, student ID: 810010101, credits: 0
Number of students: 3

This program is working and fully functional. However, there is a substantial code duplication between Student and Instructor. Your job is to eliminate this redundancy and improve the program structure by following these steps:

1. Make both Student and Instructor subclasses of Person
2. Move the common attributes (name & id) from Instructor & Student to Person
3. Move the common methods getName, setName, getID, setID, getLoginName to Person
4. Create a method print() in Person, in this method print the name of the person: System.out.print(name);
5. Modify the methods print() in Student and Instructor by making them
   • Call super.print()
   • Then printing the IDs, credits and salary respectively

Effectively the super class Person will take care of printing name, then the subclasses will provide the added functionality of displaying ID and credits (Student) and salary (Instructor)

The Main and Course classes should compile and work as usual at this point producing exactly same output as above. Happy refactoring!

The code that is given and needs to be worked on follows (There are 5 separate classes. they are Main.java, Person.java, Student.java, Course.java, Instructor.java) :

//Main.java Class

public class Main {

   public static void main(String[] args) {
       Instructor instructor = new Instructor();
       instructor.setName("Hani Javadi");
       instructor.setID("888777666");
       instructor.setSalary(11111);
       instructor.print();
      
       System.out.println("--- --- ---");
      
       Student student1 = new Student();
       student1.setName("Joe Loop");
       student1.setID("810123456");
       student1.addCredits(10);
       student1.print();
      
       System.out.println("--- --- ---");
      
       Student student2 = new Student();
       student2.setName("Mary Collection");
       student2.setID("811987321");
       student2.addCredits(25);
       student2.print();
      
       System.out.println("--- --- ---");
      
       Student student3 = new Student();
       student3.setName("Ke Method");
       student3.setID("810010101");
       student3.print();
      
       System.out.println("--- --- ---");
      
       Course course = new Course("MIST 4700", 40);
       course.setInstructor(instructor);
       course.setRoom("Z101");
       course.setTime("MWF 6am-7am");
       course.enrollStudent(student1);
       course.enrollStudent(student2);
       course.enrollStudent(student3);
      
      
       course.printList();
      
      

   }

}

//Person.java class

public class Person {

}

//Student.java Class

/**
* The Student class represents a student in a student administration system. It
* holds the student details relevant in our context.
*/
public class Student {
   // the student's full name
   private String name;
   // the student ID
   private String id;
   // the amount of credits for study taken so far
   private int credits;

   public String getName() {
       return name;
   }

   public void setName(String replacementName) {
       name = replacementName;
   }

   public String getID() {
       return id;
   }

   public void setID(String id) {
       this.id = id;
   }

   /**
   * Add some credit points to the student's accumulated credits.
   */
   public void addCredits(int additionalPoints) {
       credits += additionalPoints;
   }

   /**
   * Return the number of credit points this student has accumulated.
   */
   public int getCredits() {
       return credits;
   }

   /**
   * Return the login name of this student. The login name is a combination of the
   * first four characters of the student's name and the first three characters of
   * the student's ID number.
   */
   public String getLoginName() {
       return name.substring(0, 4) + id.substring(0, 3);
   }

   /**
   * Print the student's name and ID number to the output terminal.
   */
   public void print() {
       System.out.println(name + ", student ID: " + id + ", credits: " + credits);
   }
}

//Course.java Class

import java.util.*;

/**
* The Course class represents an enrollment list for one class. It stores the
* time, room and participants of the lab, as well as the instructor's name.
*/
public class Course {
   private String name;
   private String room;
   private String timeAndDay;
   private ArrayList<Student> students;
   private Instructor instructor;
   private int capacity;

   /**
   * Create a Course with a maximum number of enrolments. All other details are
   * set to default values.
   */
   public Course(String name, int maxNumberOfStudents) {
       this.name = name;
       instructor = new Instructor();
       room = "unknown";
       timeAndDay = "unknown";
       students = new ArrayList<Student>();
       capacity = maxNumberOfStudents;
   }

   /**
   * Add a student to this Course.
   */
   public void enrollStudent(Student newStudent) {
       boolean atCapacity = (students.size() == capacity);
       if (atCapacity == true) {
           System.out.println("The class is full, you cannot enrol.");
       } else {
           students.add(newStudent);
       }
   }

   /**
   * Return the number of students currently enrolled in this Course.
   */
   public int numberOfStudents() {
       return students.size();
   }

   /**
   * Set the room number for this Course.
   */
   public void setRoom(String roomNumber) {
       room = roomNumber;
   }

   /**
   * Set the time for this Course. The parameter should define the day and the
   * time of day, such as "Friday, 10am".
   */
   public void setTime(String timeAndDayString) {
       timeAndDay = timeAndDayString;
   }

   /**
   * Set the name of the instructor for this Course.
   */
   public void setInstructor(Instructor instructorN) {
       instructor = instructorN;
   }

   /**
   * Print out a class list with other Course details to the standard terminal.
   */
   public void printList() {
       System.out.println(name + " " + timeAndDay);
       System.out.println("Instructor: " + instructor.getName() + " Room: " + room);
       System.out.println("Class list:");
       for (Student student : students) {
           student.print();
       }
       System.out.println("Number of students: " + numberOfStudents());
   }
}

//instructor.java Class

/**
* Write a description of class Instructor here.
*/
public class Instructor {
   // the student's full name
   private String name;
   // the student ID
   private String id;
   // the amount of credits for study taken so far
   private double salary;

   public String getName() {
       return name;
   }

   public void setName(String replacementName) {
       name = replacementName;
   }

   public String getID() {
       return id;
   }

   public void setID(String id) {
       this.id = id;
   }

   public String getLoginName() {
       return name.substring(0, 4) + id.substring(0, 3);
   }

   public double getSalary() {
       return salary;
   }

   public void setSalary(double newSalary) {
       salary = newSalary;
   }

   public void print() {
       System.out.println(name + ", instructor ID: " + id + ", salary: " + salary);
   }
}

Answer 1

SOLUTION :-

CODE IN JAVA :-

Person.java

public class Person {
private String name, id;
  
public Person()
{
name = "";
id = "";
}
  
public Person(String name, String id)
{
this.name = name;
this.id = id;
}
  
public String getName()
{
return this.name;
}
  
public String getId()
{
return this.id;
}
  
public void setName(String name)
{
this.name = name;
}
  
public void setId(String id)
{
this.id = id;
}
  
public void print()
{
System.out.print(getName());
}
}

Student.java

public class Student extends Person{
private int credits;
  
public Student()
{
super();
this.credits = 0;
}
  
public Student(String name, String id, int credits)
{
super(name, id);
this.credits = credits;
}

public int getCredits() {
return credits;
}

public void setCredits(int credits) {
this.credits = credits;
}
  
@Override
public void print()
{
super.print();
System.out.println(", Student Id: " + super.getId() + ", Credits: " + getCredits() + "");
}
}

Instructor.java

public class Instructor extends Person{
private double salary;
  
public Instructor()
{
super();
salary = 0.0;
}
  
public Instructor(String name, String id, double salary)
{
super(name, id);
this.salary = salary;
}
  
public double getSalary() {
return salary;
}

public void setSalary(double salary) {
this.salary = salary;
}
  
@Override
public void print()
{
super.print();
System.out.println(", Instructor Id: " + getId() + ", Salary: $" + getSalary());
}
}

Course.java

public class Course {
private String title;
private int maxCapacity;
private Instructor instructor;
private Student[] students;
  
public Course()
{
this.title = "";
this.maxCapacity = 0;
this.instructor = null;
this.students = new Student[this.maxCapacity];
}

public Course(String title, int maxCapacity, Instructor instructor, Student[] students) {
this.title = title;
this.maxCapacity = maxCapacity;
this.instructor = instructor;
this.students = students;
}

public String getTitle() {
return title;
}

public void setTitle(String title) {
this.title = title;
}

public int getMaxCapacity() {
return maxCapacity;
}

public void setMaxCapacity(int maxCapacity) {
this.maxCapacity = maxCapacity;
}

public Instructor getInstructor() {
return instructor;
}

public void setInstructor(Instructor instructor) {
this.instructor = instructor;
}

public Student[] getStudents() {
return students;
}

public void setStudents(Student[] students) {
this.students = students;
}
  
public void print()
{
System.out.println("Course Title: " + getTitle() +
"\nMax Capacity: " + getMaxCapacity() +
"\nInstructor: " + getInstructor().getName() +
"\n\nClass list:");
for(int i = 0; i < students.length; i++)
{
System.out.print(i + 1 + ". ");
students[i].print();
}
System.out.println("\nNumber of students: " + students.length);
}
}

CourseDriver.java (Main class)

public class CourseDriver {
  
public static void main(String[] args)
{
// creating an array of students
Student[] students = {
new Student("Joe Loop", "810123456", 10),
new Student("Mary Collection", "811987321", 25),
new Student("Ke Method", "810010101", 0)
};
System.out.println(students.length + " students created!");
  
// creating an instructor
Instructor instructor = new Instructor("Hani Javadi", "888777666", 11111.0);
System.out.print("Instructor created: ");
instructor.print();
  
// creating an instance of a Course
Course course = new Course("MIST", 4700, instructor, students);
  
System.out.println("\n***** COURSE DETAILS *****\n--------------------------");
course.print();
System.out.println();
}
}