Understanding how to separate

I am trying to keep the connection in my code, but I think I cannot fully understand it. My basic understanding is that the relationship is "how the dependent classes sit on top of each other and know about each other's behavior." I know that dependency injection is one way to reduce communication and IoC.

Below is a quick example: I came to student, professor and course. The course has a list of students and a professor. I have a controller (using MVC) that injects Student and Professor objects. Will it still be considered related or closely related? That would also be a DI example, right?

Student class

public class Student {
private String firstName;
private String lastName;
private int studentID;
private int address;
private int telephone;
public String getFirstName() {
    return firstName;
}
public void setFirstName(String firstName) {
    this.firstName = firstName;
}
public String getLastName() {
    return lastName;
}
public void setLastName(String lastName) {
    this.lastName = lastName;
}
public int getStudentID() {
    return studentID;
}
public void setStudentID(int studentID) {
    this.studentID = studentID;
}
public int getAddress() {
    return address;
}
public void setAddress(int address) {
    this.address = address;
}
public int getTelephone() {
    return telephone;
}
public void setTelephone(int telephone) {
    this.telephone = telephone;
}
}

      

        
        
        
      

    

Professor's class

public class Professor {
private String firstName;
private String lastName;
private int professorID;
private int address;
private int telephone;
private int salary;
public String getFirstName() {
    return firstName;
}
public void setFirstName(String firstName) {
    this.firstName = firstName;
}
public String getLastName() {
    return lastName;
}
public void setLastName(String lastName) {
    this.lastName = lastName;
}
public int getProfessorID() {
    return professorID;
}
public void setProfessorID(int professorID) {
    this.professorID = professorID;
}
public int getAddress() {
    return address;
}
public void setAddress(int address) {
    this.address = address;
}
public int getTelephone() {
    return telephone;
}
public void setTelephone(int telephone) {
    this.telephone = telephone;
}
public int getSalary() {
    return salary;
}
public void setSalary(int salary) {
    this.salary = salary;
}
}

      

        
        
        
      

    

Course class

import java.util.List;

public class Course {
private List<Student> students;
private Professor professor;
public Professor getProfessor() {
    return professor;
}
public void setProfessor(Professor professor) {
    this.professor = professor;
}
public List<Student> getStudents() {
    return students;
}
public void setStudents(List<Student> students) {
    this.students = students;
}

}