задача за самостоятелна работа java

-----------1ви файл ILibraryBook

public interface ILibraryBook {
	public void get(Reader rdr);
	public void get();

}

------------2ри файл IReader

public interface IReader {
	public void get(LibraryBook obj);
	public void ret(LibraryBook obj);
}

-----------3ти файл Applicant

import java.util.GregorianCalendar;

public class Applicant {
				private String name;
				private GregorianCalendar date;
				private double uspeh;

				public Applicant(GregorianCalendar birth, String name, double uspeh)
				{
					this.name = name;
					this.date = birth;
					this.uspeh = uspeh;
				}

				public String getName()
				{
					return this.name;
				}
				public void setName(String name)
				{
					this.name = name;
				}
				public GregorianCalendar getDate()
				{
					return this.date;
				}
				public void setDate(GregorianCalendar birth)
				{
					this.date = birth;
				}
				public double getUspeh()
				{
					return this.uspeh;
				}
				public void setUspeh(double uspeh)
				{
					this.uspeh = uspeh;
				}
				public String toString()
				{
					return this.name + " " + this.date + " " + this.uspeh + " ";
				}
}

---------------------4ти файл Student

import java.util.GregorianCalendar;

public class Student extends Applicant implements Comparable<Object>{
	private String FN;

	public Student(String name, String FN) {
		super(new GregorianCalendar(),name,0.0);
		this.FN = FN;
	}

	public Student(GregorianCalendar date, String name, double uspeh, String FN) {
		/*super.setDate(date);
		super.setName(name);
		super.setUspeh(uspeh);*/
		super(date,name,uspeh);
		this.FN = FN;
	}

	public boolean equals (Object r) {
		return this.FN.equals(((Student)r).FN);
	}

	public String getFN() {
		return this.FN;
	}

	public void setFN(String FN) {
		this.FN = FN;
	}

	public String toString() {
		return super.toString() + " " + this.FN;
	}

	public int compareTo(Object r) {
		return this.FN.compareTo(((Student)r).FN);
	}
}

------------------------------5ти файл Reader

import java.util.GregorianCalendar;

public class Reader extends Student implements IReader,Comparable<Object>{
	private LibraryBook library_book_obj= new LibraryBook("");

	public Reader(String nm,String fn) {
		super(nm,fn);
	}

	public Reader(GregorianCalendar date, String name, double uspeh, String FN) {
		super(date,name,uspeh,FN);
	}

	public LibraryBook getLibraryBook() {
		return this.library_book_obj;
	}

	public String toString() {
		return super.toString() + " " + this.library_book_obj.toString();
	}

	public int compareTo(Object r) {
		return super.compareTo(r);
	}

	public void get(LibraryBook lb) {
		this.library_book_obj = lb;
	}

	public void ret(LibraryBook lb) {
		lb.ret();
		library_book_obj = null;
	}
}

---------------------------6ти файл LibraryBook

public class LibraryBook implements ILibraryBook,Comparable<Object>{
	private Reader reader_obj = new Reader(null, null, 0, null);
	private String book_name;
	private boolean status;

	public LibraryBook(String bn) {
		this.book_name = bn;
	}

	public LibraryBook(String bn,boolean st) {
		this.book_name = bn;
		this.status = st;
	}

	public Reader getReader() {
		return reader_obj;
	}

	public String getBookName() {
		return this.book_name;
	}

	public void setBookName(String book_name) {
		this.book_name = book_name;
	}

	public String getStatusText() {
		if(this.status) {
			return "zaeta";
		}
		return "svobodna";
	}

	public boolean getStatus() {
		return this.status;
	}

	public void setStatus(boolean status) {
		this.status = status;
	}

	public String toString() {
		return reader_obj.toString() + " " + book_name + " " + this.getStatusText();
	}

	public int compareTo(Object r) {
		return this.compareTo((LibraryBook)r).toString());    // <-----тук има грешка и подчертава всичко включително след this.
	}

	public void get(Reader rdr) {
		this.reader_obj = null;
		this.status = true;
	}

	public void ret() {
		this.reader_obj = null;
		this.status = false;
	}
}