Welcome dear expert,, I can't use the methods in bluej when I create the object of class, I don't know why can you check the code because The problem is shown in the picture and I have not found a solution yet $,$ just I want to use the methods like add course and remove etc. this is the codes of classes : import java.util.ArrayList;

class University $\{$

private String name;

private String location;

private ArrayList faculties;

public University$($String name, String location$)\{$

this.name $=$ name;

this.location $=$ location;

this.faculties $=$ new ArrayList;

$\}$

public void addFaculty$($Faculty faculty$)\{$

faculties.add$($faculty$)$;

$\}$

public void removeFaculty$($Faculty faculty$)\{$

faculties.remove$($faculty$)$;

$\}$

$\}$

class Faculty $\{$

private String name;

private ArrayList courses;

private ArrayList students;

public Faculty$($String name$)\{$

this.name $=$ name;

this.courses $=$ new ArrayList;

this.students $=$ new ArrayList;

$\}$

public void addCourse$($Course course$)\{$

courses.add$($course$)$;

$\}$

public void removeCourse$($Course course$)\{$

courses.remove$($course$)$;

$\}$

public void admitStudent$($Student student$)\{$

students.add$($student$)$;

$\}$

public void expelStudent$($Student student$)\{$

students.remove$($student$)$;

$\}$

$\}$

class Course $\{$

private String name;

private String code;

private ArrayList enrolledStudents;

public Course$($String name, String code$)\{$

this.name $=$ name;

this.code $=$ code;

this.enrolledStudents $=$ new ArrayList;

$\}$

public void enrollStudent$($Student student$)\{$

enrolledStudents.add$($student$)$;

$\}$

public void unenrollStudent$($Student student$)\{$

enrolledStudents.remove$($student$)$;

$\}$

$\}$

class Student $\{$

private String name;

private int ID;

private ArrayList enrolledCourses;

public Student$($String name, int ID$)\{$

this.name $=$ name;

this.ID $=$ ID;

this.enrolledCourses $=$ new ArrayList;

$\}$

$\}$