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Java Builder Object Printing Null

I have created a Person, class and a Professor class that both use the Builder Pattern to create objects. The Professor class takes a Person object as an argument in its constructor. I am trying to use both classes together, but when I attempt to print out a professor, get the following output: null null (instead of Bob Smith).
Here's what I tried so far:
Person:
public class Person {
private String firstname;
private String lastname;
private int age;
private String phoneNumber;
private String emailAddress;
private char gender;
public Person(){}
// builder pattern chosen due to number of instance fields
public static class PersonBuilder {
// required parameters
private final String firstname;
private final String lastname;
// optional parameters
private int age;
private String phoneNumber;
private String emailAddress;
private char gender;
public PersonBuilder(String firstname, String lastname) {
this.firstname = firstname;
this.lastname = lastname;
}
public PersonBuilder age(int age) {
this.age = age;
return this;
}
public PersonBuilder phoneNumber(String phoneNumber) {
this.phoneNumber = phoneNumber;
return this;
}
public PersonBuilder emailAddress(String emailAddress) {
this.emailAddress = emailAddress;
return this;
}
public PersonBuilder gender(char gender) {
this.gender = gender;
return this;
}
public Person build() {
return new Person(this);
}
}
// person constructor
private Person(PersonBuilder builder) {
this.firstname = builder.firstname;
this.lastname = builder.lastname;
this.age = builder.age;
this.phoneNumber = builder.phoneNumber;
this.emailAddress = builder.emailAddress;
this.gender = builder.gender;
}
#Override
public String toString() {
return this.firstname + " " + this.lastname;
}
}
Here's the Professor class:
package com.example.hardcodedloginform;
import java.util.List;
public class Professor extends Person{
private Person professor;
private double salary;
private String courseTaught;
private List<Student> students;
private int professorID;
public static class ProfessorBuilder {
// required fields
private Person professor;
private int professorID;
// optional fields
private double salary;
private String courseTaught;
private List<Student> students;
public ProfessorBuilder(Person professor, int professorID) {
this.professor = professor;
this.professorID = professorID;
}
public ProfessorBuilder salary(double salary) {
this.salary = salary;
return this;
}
public ProfessorBuilder courseTaught(String courseTaught) {
this.courseTaught = courseTaught;
return this;
}
public ProfessorBuilder students(List<Student> students) {
this.students = students;
return this;
}
public Professor build() {
return new Professor(this);
}
}
private Professor(ProfessorBuilder builder) {
this.salary = builder.salary;
this.courseTaught = builder.courseTaught;
this.students = builder.students;
}
#Override
public String toString() {
return "" + super.toString();
}
}
And here is the Main class where I try to print out a professor object:
public class Main {
public static void main(String[] args) {
Person profBobs = new Person.PersonBuilder("Bob", "Smith")
.age(35)
.emailAddress("bob.smith#SNHU.edu")
.gender('M')
.phoneNumber("818-987-6574")
.build();
Professor profBob = new Professor.ProfessorBuilder(profBobs, 12345)
.courseTaught("MAT101")
.salary(15230.01)
.build();
System.out.println(profBob);
}
}
I would like the printout in the console to be "Bob Smith", but what I am seeing is: null null. I checked and found that the Person object profBobs is, in fact, created properly and does print out the name "Bob Smith" when I attempt to print it the same way. I don't know why my Professor prints: null null.

Your Professor constructor fails to initialise any member fields of its base class.
There are multiple ways to solve this. One solution has ProfessorBuilder extend PersonBuilder:
public class Professor extends Person {
// Remove the `person` field! A professor *is-a* person, it does not *contain* it.
private double salary;
private String courseTaught;
private List<Student> students;
private int professorID;
public static class ProfessorBuilder extends Person.PersonBuilder {
// required fields
private int professorID;
// optional fields
private double salary;
private String courseTaught;
private List<Student> students;
public ProfessorBuilder(Person professor, int professorID) {
super(professor);
this.professorID = professorID;
}
// …
}
private Professor(ProfessorBuilder builder) {
super(builder);
this.salary = builder.salary;
this.courseTaught = builder.courseTaught;
this.students = builder.students;
}
}
For this to work you also need to mark the Person constructor as protected rather than private.
Furthermore, your Professor.toString method implementation made no sense: it essentially just called the base class method, so there’s no need to override it. And prepending the empty string does nothing.

Add new parameters in for using Java ArrayList

I am a beginner using Java and I don't find the solution for this:
public class Company{
private String name;
private int age;
public Company(String n, int a){
name = n;
age = a;
}
/*get and set*/
public static void main(String[] args) {
ArrayList<Company> comp = new ArrayList<Company>();
comp.add(new Company("Tom", 23));
comp.add(new Company("John", 43));
comp.add(new Company("Charles", 25));
}
}
I would like to add parameters in a for, like email, address, etc. But .add is for new elements, no parameters.

Extend the Company class with the email, address fields (1), update the constructor (2), and pass the arguments you want (3).
public class Company {
...
private final String address; // 1
private final String email;
public Company(String n, int a, String address, String email) { // 2
...
this.address = address;
this.email = email;
}
public static void main(String[] args) {
...
comp.add(new Company("Charles", 25, "street", "charles#gmail.com")); // 3
}
}
If you already have an array filled with information for a specific field, you can use a for:
final List<String> emails = Arrays.asList("first#gmail.com", "second#gmail.com");
for (final String email : emails) {
comp.add(new Company(..., ..., ..., email));
}

You need to read about class members.
public class Company{
private String name;
private int age;
private String email;
private String address;
public Company(String n, int a, String e, String addr){
name = n;
age = a;
email = e;
address = addr;
}

First, you need to add variables to your class (that is the place where it will be stored per each class instance, as well as name or age are at the moment
Than you have to modify constructor (or create another one) to be able take these parameters, and also it is good idea to make getters and setters to get or set these parameters individually, so it can looks like this
public class Company{
private String name;
private int age;
private String email;
private String address;
public Company(String n, int a){
name = n;
age = a;
}
public Company(String n, int a,String email, String address){
name = n;
age = a;
this.email = email; //class instance object email is set to email from method parameter
this.address = address;
}
/*get and set*/
public void setEmail(String email){
this.email=email; //explicit setter
}
public String getEmail(){
return this.email;
}
public static void main(String[] args) {
ArrayList<Company> comp = new ArrayList<Company>();
comp.add(new Company("Tom", 23)); //will work, because I let your constructor
comp.add(new Company("John", 43));
comp.add(new Company("Charles", 25));
Company compToAdd= new Company("preparedFoo",22);
compToAdd.setEmail("fooomail"); //will work because setter
comp.add(compToAdd);
comp.add(new Company("FooName", 30,"fooMail","FooAddress")); //will work because new constructor
}
}

Java ,import not resolved,inheritance,inner class

Begging java programming recently, run into an error. please help
Have two classes , PersonTest.java:
public class PersonTest {
public static void main(String[] args) {
Person person1=new Person("dummy","sdymmt","20","male","washington");
System.out.println("Name: "+person1.getName());
System.out.println("Surname: "+person1.getSurname());
System.out.println("Age: "+person1.getAge());
System.out.println("Gender:" +person1.getGender());
System.out.println("Birthplace: "+person1.getBirthplace());
Person person2= new Person(400);
System.out.println("Income:"+person2.getX()+" mije leke");
System.out.println("Tax:"+person2.Taksat()+" mije leke");
Student student1= new Student("adsd","zedsdsadza");
System.out.println("emri"+student1.getEmer());
}
}
and also Person.java :
public class Person {
private String Name;
private String Surname;
private String Age;
private String Gender;
private String Birthplace;
private double x;
public Person()
{
}
public Person(String Name, String Surname, String Age, String Gender, String Birthplace) {
this.Name = Name;
this.Surname = Surname;
this.Age = Age;
this.Gender = Gender;
this.Birthplace = Birthplace;
}
public String getName() {
return Name;
}
public String getSurname() {
return Surname;
}
public String getAge() {
return Age;
}
public String getGender() {
return Gender;
}
public String getBirthplace() {
return Birthplace;
}
public Person(double x) {
this.x = x;
}
public double getX() {
return x;
}
double Taksat() {
return (0.1 * x);
}
public class Student extends Person {
private String University;
private String Faculty;
public Student(String Universiteti, String Fakulteti) {
super(Name, Surname, Age, Gender, Birthplace);
this.Faculty = Fakulteti;
this.University = Universiteti;
}
public String getFaculty() {
return Faculty;
}
public String getUniversity() {
return University;
}
}
}
Two classes are in the same default package. How to fix the fact that the test class doesn't recognize the inner class student as a class.

Nested non static class are called Inner Classes those classes cannot live without the Outer class (which wrapped them).
Java docs
An instance of InnerClass can exist only within an instance of
OuterClass and has direct access to the methods and fields of its
enclosing instance.
To instantiate an inner class, you must first instantiate the outer
class. Then, create the inner object within the outer object with this
syntax:
OuterClass.InnerClass innerObject = outerObject.new InnerClass();
Try using:
Person.Student student = person1.new Student(PARAMETERS);
Important Mark:
Of course, you should highly consider that this is not a good design, because you may want this classes to be visible outside of the Person class but also because Person.Student inherits from Person, which it's already contains the Student class, which usually looks like a loop or a circle relationship, which usually not a good idea for the first place.

Because there is no Student class. Since it nested, it's Person.Student

Adding objects of a class to an ArrayList in another class

Im trying to add Objects of a Class called Student to an Arraylist in another class called StudentClass. I have initialised the list, but am having trouble working out how to add objects to the ArrayList
Code for StudentClass
public class StudentClass
{
List<Student> studentList;
private String studentName;
private int lengthOfString;
public StudentClass()
{
super();
studentList = new ArrayList<>();
}
public void addStudent(String aName)
{
String objt = new String(name, mark);
studentList.add(Student);
}
Code for Student
public class Student
{
private String name;
private int mark;
public Student(String aName)
{
super();
this.name = aName;
this.mark = -1;

Try this:
public void addStudent(String aName) {
studentList.add(new String(aName));
}
Also, Student class constructor does not accept marks as second parameter, at least the code what you have posted.

This should work.
import java.util.*;
public class StudentClass
{
List<Student> studentList;
private String studentName;
private int lengthOfString;
public StudentClass()
{
super();
studentList = new ArrayList<>();
}
public void addStudent(String aName) {
Student student = new Student(aName);
studentList.add(student);
}
}
public class Student
{
private String name;
private int mark;
public Student(String aName)
{
super();
this.name = aName;
this.mark = -1;
}
}
I'm not clear what you're trying to do with the mark?

Seems that your mistake is here:
String objt = new String(name, mark);
studentList.add(Student);
Write this instead:
Student objt = new Student(name, mark);
studentList.add(objt);

You need to create a new Student object and then add that to your list:
public void addStudent(String aName) {
Student student = new Student(aName);
studentList.add(student);
}
It's not really clear from your provided code how the mark field is set, but either pass it through the Student construction and/or add getters and setters.

How to use a variable of one class, in another in Java?

I'm just working through a few things as practice for an exam I have coming up, but one thing I cannot get my head round, is using a variable that belongs to one class, in a different class.
I have a Course class and a Student class. Class course stores all the different courses and what I simply want to be able to do is use the name of the course, in class Student.
Here is my Course class:
public class Course extends Student
{
// instance variables - replace the example below with your own
private Award courseAward;
private String courseCode;
public String courseTitle;
private String courseLeader;
private int courseDuration;
private boolean courseSandwich;
/**
* Constructor for objects of class Course
*/
public Course(String code, String title, Award award, String leader, int duration, boolean sandwich)
{
courseCode = code;
courseTitle = title;
courseAward = award;
courseLeader = leader;
courseDuration = duration;
courseSandwich = sandwich;
}
}
And here is Student:
public class Student
{
// instance variables - replace the example below with your own
private int studentNumber;
private String studentName;
private int studentPhone;
private String studentCourse;
/**
* Constructor for objects of class Student
*/
public Student(int number, String name, int phone)
{
studentNumber = number;
studentName = name;
studentPhone = phone;
studentCourse = courseTitle;
}
}
Am I correct in using 'extends' within Course? Or is this unnecessary?
In my constructor for Student, I am trying to assign 'courseTitle' from class Course, to the variable 'studentCourse'. But I simply cannot figure how to do this!
Thank you in advance for your help, I look forward to hearing from you!
Thanks!

Am I correct in using 'extends' within Course? Or is this unnecessary?
Unfortunately not, if you want to know whether your inheritance is correct or not, replace extends with is-a. A course is a student? The answer is no. Which means your Course should not extend Student
A student can attend a Course, hence the Student class can have a member variable of type Course. You can define a list of courses if your model specifies that (a student can attend several courses).
Here is a sample code:
public class Student{
//....
private Course course;
//...
public void attendCourse(Course course){
this.course = course;
}
public Course getCourse(){
return course;
}
}
Now, you can have the following:
Student bob = new Student(...);
Course course = new Course(...);
bob.attendCourse(course);

I assume a Course is not a Student, so inheritance between those classes is probably a bad idea.

You have to declare them public.
A better way is the keep them private, and code a public getter for that variable. for example:
public Award getCourseAward(){
return this.courseAward;
}

Course should not extend Student. If you want to access the courseTitle field of Course, you need to pass a reference to a Course object to the Student and then do course.CourseTitle.

You cannot access private attributes of a class from another, this is one of the main principles of OOP: encapsulation. You have to provide access method to those attribute, you want to publish outside the class. The common approach is setter/getters - getters only, if you want to have your class immutable. Look here: http://en.wikipedia.org/wiki/Mutator_method#Java_example

It does not make sense to arbitrarily extend classes. Student is not a Course or vice versa, so you cannot extend them like that.
What you need to do is:
create a Course first:
Course aCourse = new Course(..);
create a Student:
Student aStudent = new Student(..);
assign the Course to the Student:
aStudent.setCourse(aCourse.title);

Extending Student with Couse because they are not of the same kind. Extending one class with another happens when specializing a more general (in a sense) one.
The solution would be to pass courseTitle as an argument of the Student constructor

There should be 3 separate objects here, a Course, a Student, and an Enrollment. An enrollment connects a Student to a Course, a Course has many Students, and a Student can enroll in many courses. None of them should extend each other.

First,
You are extending Student class in Course class, which means, student class gets all the coruse class properties. So, the student class does not have the courseTitle property.
Second, yes, it is unnesessary - you need to do the following:
public class Course
{
private Award courseAward;
private String courseCode;
public String courseTitle;
private String courseLeader;
private int courseDuration;
private boolean courseSandwich;
public Course(String code, String title, Award award, String leader, int duration, boolean sandwich)
{
courseCode = code;
courseTitle = title;
courseAward = award;
courseLeader = leader;
courseDuration = duration;
courseSandwich = sandwich;
}
}
public class Student
{
private int studentNumber;
private String studentName;
private int studentPhone;
// This is where you keep the course object associated to student
public Course studentCourse;
public Student(int number, String name, int phone, Course course)
{
studentNumber = number;
studentName = name;
studentPhone = phone;
studentCourse = course;
}
}
Example usage would be something like this:
Course course = new Course("ASD", "TITLE", null, "ME", 50, true);
Student student = new Student(1, "JOHN", "5551234", course);
And then, get the course information you need from student via, i.e.:
student.studentCourse.courseTitle;
Since now student.studentCourse will be a course object with all of its properties.
Cheers,

Maybe you do not need to add the course name to student. What I would do is add Students to some datastructure in Course. This is cleaner and reduces the coupling between Course and Student. This would also allow you to have Students being in more than one course. For example:
public class Course extends Student{
private Award courseAward;
private String courseCode;
public String courseTitle;
private Student courseLeader;//change to a student Object
private int courseDuration;
private boolean courseSandwich;
private Set<Student> students;//have course hold a collection of students
/**
* Constructor for objects of class Course
*/
public Course(String code, String title, Award award, Student leader, int duration, boolean sandwich){
courseCode = code;
courseTitle = title;
courseAward = award;
courseLeader = leader;
courseDuration = duration;
courseSandwich = sandwich;
this.students=new HashSet<Student>();
}
public boolean addStudent(Student student){
return students.add(student);
}
public Set<Student> getStudents(){
return students;
}
}

As mentioned, stay away from the "extends" for this. In general, you shouldn't use it unless the "is-a" relationship makes sense.
You should probably provide getters for the methods on the Course class:
public class Course {
...
public String getTitle() {
return title;
}
}
And then if the Student class needs that, it would somehow get a hold of the course (which is up to you in your design), and call the getter:
public class Student {
private Set<Course> courses = new HashSet<Course>();
public void attendCourse(Course course) {
courses.add(course);
}
public void printCourses(PrintStream stream) {
for (Course course : courses) {
stream.println(course.getTitle());
}
}
}

Here below find out the solution of your problem and if you want to check below code on your machine then create a file named Test.java and paste the below codes:
package com;
class Course
{
private Award courseAward;
private String courseCode;
public String courseTitle;
private String courseLeader;
private int courseDuration;
private boolean courseSandwich;
public Course(String code, String title, Award award, String leader, int duration, boolean sandwich)
{
courseAward = award;
courseCode = code;
courseTitle = title;
courseLeader = leader;
courseDuration = duration;
courseSandwich = sandwich;
}
public Award getCourseAward() {
return courseAward;
}
public void setCourseAward(Award courseAward) {
this.courseAward = courseAward;
}
public String getCourseCode() {
return courseCode;
}
public void setCourseCode(String courseCode) {
this.courseCode = courseCode;
}
public String getCourseTitle() {
return courseTitle;
}
public void setCourseTitle(String courseTitle) {
this.courseTitle = courseTitle;
}
public String getCourseLeader() {
return courseLeader;
}
public void setCourseLeader(String courseLeader) {
this.courseLeader = courseLeader;
}
public int getCourseDuration() {
return courseDuration;
}
public void setCourseDuration(int courseDuration) {
this.courseDuration = courseDuration;
}
public boolean isCourseSandwich() {
return courseSandwich;
}
public void setCourseSandwich(boolean courseSandwich) {
this.courseSandwich = courseSandwich;
}
}
class Student
{
private int studentNumber;
private String studentName;
private int studentPhone;
private Course studentCourse;
/**
* Constructor for objects of class Student
*/
public Student(int number, String name, int phone, Course course)
{
studentNumber = number;
studentName = name;
studentPhone = phone;
studentCourse = course;
}
public int getStudentNumber() {
return studentNumber;
}
public void setStudentNumber(int studentNumber) {
this.studentNumber = studentNumber;
}
public String getStudentName() {
return studentName;
}
public void setStudentName(String studentName) {
this.studentName = studentName;
}
public int getStudentPhone() {
return studentPhone;
}
public void setStudentPhone(int studentPhone) {
this.studentPhone = studentPhone;
}
public Course getStudentCourse() {
return studentCourse;
}
public void setStudentCourse(Course studentCourse) {
this.studentCourse = studentCourse;
}
}
class Award{
private long awardId;
private String awardName;
Award(long awardId, String awardName){
this.awardId = awardId;
this.awardName = awardName;
}
public long getAwardId() {
return awardId;
}
public void setAwardId(long awardId) {
this.awardId = awardId;
}
public String getAwardName() {
return awardName;
}
public void setAwardName(String awardName) {
this.awardName = awardName;
}
}
public class Test{
public static void main(String ar[]){
// use your all classes here
}
}