java file

/*
* 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");

}
}

Document.java

/*
* Simple Document class
*/
public class Document
{
private String id;
private String header;
private String body;
private String footer;

public Document(String id)
{
this.id = id;
this.footer = "";
this.header = "";
this.body = "";
}

public void print()
{
System.out.println(header + "\n\n" + body + "\n\n" + footer);
}

public String getId()
{
return id;
}

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

public String getHeader()
{
return header;
}

public void setHeader(String header)
{
this.header = header;
}

public String getBody()
{
return body;
}

public void setBody(String body)
{
this.body = body;
}

public String getFooter()
{
return footer;
}

public void setFooter(String footer)
{
this.footer = footer;
}
}

Expense Document.java

import java.util.ArrayList;

//-----------Start below here. To do: approximate lines of code = 1
// Make the class ExpenseDocument a subclass of Document

//-----------------End here. Please do not remove this comment. Reminder: no changes outside the todo regions.
{
private String employeeName, employeeId;
private ArrayList items;


public ExpenseDocument(String id, String name, String employeeId)
{
super(id);
this.employeeName = name;
this.employeeId = employeeId;
items = new ArrayList();
}

//Overrides the print() method in class Document
public void print()
{
String itemList = "";

//-----------Start below here. To do: approximate lines of code = 5
// Set the document header to "Expense Report"
// Then append each item in the list of items to the itemList variable above.
// Append each item to itemList (declared above) by adding the item number (indexed from 1) followed by a ". " followed by
// the item string itself followed by a "\n". Set the document body variable to the employee name followed by
// " Employee Id: " followed by the employeeId followed by "\n\nExpenses:\n" followed by string itemList; Then
// print the expense report by using the print() method in the superclass Document







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

//-----------Start below here. To do: approximate lines of code = 2
// Create a method void addItem(String item) that adds the expense item to the array list of items




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

//-----------Start below here. To do: approximate lines of code = 2
// Create a method void clearItems() that removes all the items from array list of items
//Hint: look at the documentation for class ArrayList for a suitable method to use




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

DonationReceipt.java

/*
* A DonationReceipt is a Document that specifies the receiver has donated an amount of money to a charitable
* organization
*/
//-----------Start below here. To do: approximate lines of code = 1
// make class DonationReceipt a subclass of Document

//-----------------End here. Please do not remove this comment. Reminder: no changes outside the todo regions.
{
private String organization;
private String receiver;
private String address;
private String receiptNumber;
private String amount;
private String date;

public DonationReceipt(String id)
{
super(id);
}

public DonationReceipt(String id, String receiver, String organization, String number, String amount, String date)
{
super(id);
this.receiver = receiver;
this.organization = organization;
this.receiptNumber = number;
this.amount = amount;
this.date = date;
}

// Set the body of the receipt. Overrides the setBody() method in Document
public void setBody(String receiptBody)
{
//-----------Start below here. To do: approximate lines of code = 2
// Set the string body variable, inherited from Document, to contain
// the given receiptBody string followed by the receiver followed by "\n\nReceipt#: " followed by
// the receiptNumber followed by "\nAmount: " followed by the amount followed by "\nDate: " followed by the date string


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

public String getOrganization()
{
return organization;
}

public void setOrganization(String organization)
{
this.organization = organization;
}

public String getReceiver()
{
return receiver;
}

public void setReceiver(String receiver)
{
this.receiver = receiver;
}

public String getAddress()
{
return address;
}

public void setAddress(String address)
{
this.address = address;
}

public String getReceiptNumber()
{
return receiptNumber;
}

public void setReceiptNumber(String receiptNumber)
{
this.receiptNumber = receiptNumber;
}

public String getAmount()
{
return amount;
}

public void setAmount(String amount)
{
this.amount = amount;
}

public String getDate()
{
return date;
}

public void setDate(String date)
{
this.date = date;
}



}

If you can please double check all works smoothly and have extra screenshots of the output showing as expected. Thank you