/*
* A simple program to test a class Professor
*/
public class QO3
{
public static void main(String[] args) {

Professor rachel = new Professor("Rachel");
Professor joey = new Professor("Joey");
Professor ross = new Professor("Ross");
Professor monica = new Professor("Monica");
Professor chandler = new Professor("Chandler");
Professor phoebe = new Professor("Phoebe");

rachel.addCollaborator(joey);
rachel.addCollaborator(ross);
rachel.addCollaborator(monica);
rachel.addCollaborator(chandler);
rachel.addCollaborator(phoebe);

joey.addCollaborator(rachel);
joey.addCollaborator(ross);
joey.addCollaborator(monica);
joey.addCollaborator(chandler);
joey.addCollaborator(phoebe);

System.out.println(rachel.collaboratorsInCommon(joey));
System.out.println(joey.collaboratorsInCommon(rachel));

rachel.delCollaborator(monica);
System.out.println(rachel.collaboratorsInCommon(joey));
rachel.delCollaborator(chandler);
System.out.println(rachel.collaboratorsInCommon(joey));
rachel.delCollaborator(phoebe);
System.out.println(rachel.collaboratorsInCommon(joey));
rachel.delCollaborator(ross);
System.out.println(rachel.collaboratorsInCommon(joey));
System.out.println("Expected:\nRoss Monica Chandler Phoebe\nRoss Monica Chandler Phoebe\nRoss Chandler Phoebe\nRoss Phoebe\nRoss");

}
}

Next file:

import java.util.ArrayList;
/*
* A Professor has a name and a list of Professors with whom they collaborate on research projects
*/
public class Professor
{
private String name;
private ArrayList collaborators;

/**
* Initializes name and collaborators variables
*/
public Professor(String nm)
{
  //-----------Start below here. To do: approximate lines of code = 2
  // initialize instance variable name to nm, initialize collaborators to an empty array list
 
 
  //-----------------End here. Please do not remove this comment. Reminder: no changes outside the todo regions.
}

/** Retrieves the name of the proferssor
* @return a string containing the professor's name
*/
public String getName()
{
return name;
}

/** Adds a professor to the list of collaborators of this professor
* @param collaborator the professor to be added
*/
public void addCollaborator(Professor collaborator)
{
//-----------Start below here. To do: approximate lines of code = 1
// add Professor collaborator to the collaborators array list

//-----------------End here. Please do not remove this comment. Reminder: no changes outside the todo regions.
}

/** Removes a professor from the list of collaborators of this person.
* @param collaborator the Professor to be removed
*/
public void delCollaborator(Professor p)
{
//-----------Start below here. To do: approximate lines of code = 1
// removes the professor p from the collaborators list.

//-----------------End here. Please do not remove this comment. Reminder: no changes outside the todo regions.
}

/**
* Returns the array list of Professors representing the collaborators
*
*/
public ArrayList getCollaborators()
{
return collaborators;
}
/*
* Searches the collaborators list of this professor and the other professor's list
* to see if they have collaborators in common.  
* @return a string containing the names of common collaborators where the names are separated by a " "
* Ensure there is no space character after the last collaborator name
* return the empty string "" if there are no collaborators in common
*/
public String collaboratorsInCommon(Professor other)
{
//-----------Start below here. To do: approximate lines of code = 10
// Hint: professors in common should not contain this professor name or other professor name











//Hint: remove any space characters at the end of the string. Make sure the string is not "" before removing spaces



//-----------------End here. Please do not remove this comment. Reminder: no changes outside the todo regions.
}

}