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How to add a user-defined data type into a set?

this is my mock test from my professor and I having trouble writing it in Java.
This is the question:
An ADT to manage a collection of students in a course is required. You
can assume that there are no more than 100 students in any course. A
student's record consists of ID (String), name (String), and GPA
(double). There is no duplication in student IDs, but it is possible
to have two or more students with the same name and/or GPA.
Create a new type StudentCollection (it is equivalent to a class in
Java). Except for the constructor, your StudentCollection type must
support the following 3 public operations (feel free to add additional
private operations as needed - but their scope have to be private)
void addStudent(Student std): add a new student std to your
collection. If there is a student having the same ID as std in your
collection already, do nothing.
Student searchByName(String name): search the student collection and
return any student whose name contains name completely (case
sensitive). Examples: "ABC" contains "ABC" completely; "ABC" contains
"A" completely; "ABC" contains "C" completely, "ABC DEF" contains "C
D" completely; "ABC" does NOT contain "CB" completely; "ABC" does NOT
contain "abc" completely. If there is more than one matching student,
your method can return any student. If there is no matching student,
return null. int rankStudent(String sID): return the rank of a student
whose ID is sID with regard to this collection. The ranking is done
using students' GPAs. A student with the highest GPA has a rank of 1.
In this example, let assume there are 4 GPA values [9.0, 8.5, 7.0,
8.5]. A student whose GPA = 9.0 has a rank of 1, a student whose GPA = 8.5 has a rank of 2 (there are 2 students who have the same rank of 2), and a student whose GPA = 7.0 has a rank of 4. If there is no
student found with the provided sID, return -1.
Create a StudentCollection object and use it in the main method
(client code). Your client code must call all the above 3 public
methods one or more times.
You are NOT allowed to use the Java Collection Framework classes for
this problem. Your code for this problem must be stored in a single
file StudentCollection.java.
The ADT I'm choosing here is Set. Since the instruction doesn't allow me to use the Java Collection Framework, I have to manually implement all of the functions.
But here is the problem:
for the first function, the question ask me to write void addStudent(Student std) which when implementing a Set ADT, I cannot pass in a user defined data type Student into the function, I have done some research and we have to pass in a Set parameter instead of a user defined data type. Here is the code for class Student:
static class Student {
private String ID;
private String name;
private double GPA;
Student(String ID, String name, double GPA) {
this.ID = ID;
this.name = name;
this.GPA = GPA;
}
}
let's say that we put in the Student class, then there have to be some getters and setters inside of the Student class. But the question limit the amount of public function to implement and all functions beside the three specify function above have to be private. How can a getter and setter be private? Is it possible?
The overall question is: How to add a user-defined data type into a set?
I'm sorry if there is any explanation of mine is not clear. Please reply to this question if you have any further question.
Here is the code that I have been working on:
import java.util.HashSet;
import java.util.Set;
public class StudentCollection {
static Set<Student> manage = new HashSet<>();
static class Student {
private String ID;
private String name;
private double GPA;
Student(String ID, String name, double GPA) {
this.ID = ID;
this.name = name;
this.GPA = GPA;
}
}
public static void addStudent(Student std) {
manage.add(std);
}
// public static Student searchByName(String name) {
//
// }
//
// public static int rankStudent(String sID) {
//
// }
public static void main(String[] args) {
Student std = new Student("s387", "nam", 3.7);
addStudent(std);
}
}

The Student class has to be public, with public getters. Otherwise, you couldn't create a Student instance to add a student.
I went ahead and coded the addStudent method. I'm leaving the rest of the code for you to finish.
You'll have to go over your class notes to verify, but this is how I would start coding the StudentCollection class. There are no static fields or methods, other than the main method.
public class StudentCollection {
public static void main(String[] args) {
StudentCollection sc = new StudentCollection();
sc.addStudent(sc.new Student("10001", "George", 9.0));
}
private int studentLength;
private Student[] students;
public StudentCollection() {
this.studentLength = 0;
this.students = new Student[100];
}
public void addStudent(Student student) {
for (int index = 0; index < studentLength; index++) {
if (student.getSID().equals(students[index].getSID())) {
return;
}
}
students[studentLength++] = student;
}
public Student searchByName(String name) {
}
public int rankStudent(String sID) {
}
public class Student {
private final double gpa;
private final String sID, name;
public Student(String sID, String name, double gpa) {
this.sID = sID;
this.name = name;
this.gpa = gpa;
}
public double getGpa() {
return gpa;
}
public String getSID() {
return sID;
}
public String getName() {
return name;
}
}
}

How to create user defined immutable class in Java which is having user defined class object as a class member?

I want to make my immutable class EmployeeDetails which has Employee object in it. I have followed conditions to make class immutable:
1. class is final
2. class members are final
3. no setters
If EmployeeDetails is immutable, I should not be able to change content in it. Still, I can change employee name or id.
What I am missing here?
public class TestImmutable{
public static void main(String args[]){
EmployeeDetails empd1 = new EmployeeDetails("ABC", new Employee(1, "n1"));
System.out.println("Id : " + empd1.getEmployee().getId());
System.out.println("Name : " + empd1.getEmployee().getName());
System.out.println("Empr : " + empd1.getEmployer());
empd1.getEmployee().setId(2);
empd1.getEmployee().setName("n2");
System.out.println("\nId : " + empd1.getEmployee().getId());
System.out.println("Name : " + empd1.getEmployee().getName());
System.out.println("Empr : " + empd1.getEmployer());
}
}
final class EmployeeDetails{
private final String employer;
private final Employee emp1;
public EmployeeDetails(String employer, Employee emp1){
this.employer = employer;
this.emp1 = emp1;
}
public String getEmployer(){
return this.employer;
}
public Employee getEmployee(){
return this.emp1;
}
}
class Employee{
public int id;
public String name;
public Employee(int id, String name){
this.id = id;
this.name = name;
}
public int getId(){
return this.id;
}
public String getName(){
return this.name;
}
public void setId(int id){
this.id = id;
}
public void setName(String name){
this.name = name;
}
}

Get rid of getEmployee(). You shouldn't be able to reach Employee emp1 outside EmployeeDetails. If you need access to the fields in Employee emp1, then provide public methods that return them.
For example:
final class EmployeeDetails{
private final String employer;
private final Employee emp1;
public EmployeeDetails(String employer, Employee emp1){
this.employer = employer;
this.emp1 = emp1;
}
public String getEmployer(){
return this.employer;
}
public String getEmployeeName() {
return this.emp1.getName();
}
...
}

I have followed conditions to make class immutable: 1. class is final
2. class members are final 3. no setters
The conditions you have laid out are necessary but not sufficient to make a class immutable. Confused?
Immutability is about preserving the state of class instances for all time. Once an instance of a class is created, then all the attributes that comprise the state of that instance must remain forever unchanged.
What happens if 1 through 3 above are satisfied, but one of your instance fields is a mutable class? In this case, returning the reference to that instance field to a client makes it possible for the client to mutate the state of your supposedly immutable class.
One solution is to perform defensive copying upon all instance fields of the immutable class that are, themselves, mutable. Instead of...
public Employee getEmployee(){
return this.emp1;
}
change this code so that a new copy of the Employee object is returned to the client. This assures that clients can not get a reference to the internal state of the instances of your immutable class:
public Employee getEmployee(){
return this.emp1.clone(); // this solution assumes that Employee
// is safely cloneable, which requires some
// care on your part. An alternative is
// to define a copy constructor in the
// Employee class and: return new Employee(emp1);
}
Defensive copying is necessary for all mutable components of an immutable class, and this rule must be applied during both construction and field access. Otherwise, you make it possible for client code to retain a reference to the mutable internal state of your class.

Making a variable final means that you cannot assign it again to some other object. You can still modify the state of the object whose reference it holds.
In this case :
final class EmployeeDetails{
private final String employer;
**private final Employee emp1;**
}
You cannot assign emp1 to a new object but you can still change the state of the employee object as it is not immutable. You can make Employee objects immutable by removing all the setters.

The EmployeeDetails class is not immutable. You have followed the usual rules for immutability except one. In Joshua Bloch's Effective Java this rule is stated as follows:
Ensure exclusive access to any mutable componenent.
In your case, since the class Employee is mutable, you need to copy Employee instances in the getter and the constructor.
public Employee getEmployee() {
return new Employee(emp1.getId(), empl.getName()); // Copy
}
public EmployeeDetails(String employer, Employee emp1){
this.employer = employer;
this.emp1 = new Employee(emp1.getId(), empl.getName()); // Copy
}
Since this version uses copies, it is not possible to modify the internals of the EmployeeDetails class.
This solution is very common. For example, the String class is immutable. Both the constructor String(char[] value) and the method char[] toCharArray() make copies of the array. This is necessary because arrays are mutable.
Another solution, which may be more appropriate for your situation, is to make Employee immutable as well.
You could even get rid of the Employee class completely and just use two fields in the EmployeeDetails class.

Initialize each element of the array with Student objects

public class Student {
int marks;
String name;
char sex;
String email;
}
Student[] s = new Student[10];
public class StudentDemo {
Student s[] = new Student[10];// array Student//
Student s1 = new Student();// Student Object//
s1.setName("John"); //Eclipse says here there is a mistake an ask to delete John//
Student[0]=s1;
}
I have created a Student class with name and other attributes. But now I want to initialize each element of the array with Student objects. Is this code right? Eclipse throws a lot of red dots.
Help.

class Student {
int marks;
String name;
char sex;
String email;
public void setName(String string)
{
// TODO Auto-generated method stub
}
}
public class StudentDemo{
public static void main(String [] args)
{
Student s[] = new Student[10];// array Student//
Student s1 = new Student();// Student Object//
s1.setName("John"); //Eclipse says here there is a mistake an ask to delete John//
s[0]=s1;
}
}
Try this.
Problems in your code:
You wrote your function logic outside of function. Corrected in my
code using main method.
You can't have 2 public classes in a class file. So i made Student file as non-public.
You din't have setter for name property of Student.

Well you never defined a setName method so I am assuming thats why you got the compiler error. Something like this should work inside the Student class
public String setName(String name){
this.name = name;
}

use the reference of the array you created instead of the type of array
Thus, replace Student[0] with s[0]

A lot is wrong with your code.
It should be
Student[] s = new Student[10];
s[0] = new Student();
s[0].setName();
You need to also write your code inside a method. Like so:
public void doStuffHere()
{
// Code goes here.
}
Notice I use that fact that at position 0 there is a Student object and then I just set the name. There is no real reason to use s1.

A few things:
First of all, your first array should be written like this:
Student[] s = new Student[10];
Secondly, you never defined the method setName(String name) in your Student class. This would look something like this:
public void setName(String name)
{
this.name = name;
}
On top of that, you can't just call the method in the class, it needs to go inside a method, constructor, or initialisation block.
For example:
public class StudentDemo
{
Student[] studentArray = initStudentArray();
private Student[] initStudentArray()
{
Student[] ret = new Student[10];
Student s = new Student();
s.setName("John");
ret[0] = s;
...
return ret;
}
}

This can help you.
class Student {
int marks;
String name;
char sex;
String email;
void setName(String name){
this.name = name; //this.name represents the current instance non-static variable
}
public String toString(){ //Overridden Objectclass method for string representation of data
return " Student Name: "+name+
"\n Gender: "+sex+
"\n Email: "+email+
"\n Marks: "+marks;
}
}
public class StudentDemo {
public static void main(String[] args){
Student s[] = new Student[10];
s[0] = new Student();
s[0].setName("John"); //similarly u can set values to other attributes of this object
System.out.println(s[0]); // same as s[0].toString() its an implicit call
}
}

How do I use Java getters and setters with a collection of data without explicitly typing out the attributes for each item?

I am very new to Java and to programming in general, and I have an assessment to complete where I load employees (with name, age, and department attributes; department can be only one of four enumerated values) into a program that will sort them by age and tell if the age is a prime number. The assignment requires Company, Department, and Employee classes. I am confident that I can figure out age/prime components — I know how to google for algorithms. What I am struggling with is putting all the discrete pieces into a cohesive whole.
Here is what I have so far. I've put in one employee, but the way I'm doing it seems completely inelegant and inefficient. I am sure there is a better way, but I've hit a mental block.
EDIT: as was pointed out below, I was unclear. What I am asking help with is populating the data structure.
Company class:
public class Company {
static Employee one = new Employee();
public static void main(String[] args) {
one.setName("Counting Guru");
one.setAge(55);
one.setDepartment(DepartmentList.ACCOUNTING);
}
}
DepartmentList class:
import java.util.EnumMap;
import java.util.Map;
import java.util.Set;
public enum DepartmentList {
ACCOUNTING, MARKETING, HUMANRESOURCES, INFORMATIONSYSTEMS;
public static void main(String[] args) {
Map<DepartmentList,String>
enumMap=new EnumMap<DepartmentList,String>(DepartmentList.class);
enumMap.put(DepartmentList.ACCOUNTING, "Accounting");
enumMap.put(DepartmentList.MARKETING, "Marketing");
enumMap.put(DepartmentList.HUMANRESOURCES, "Human Resources");
enumMap.put(DepartmentList.INFORMATIONSYSTEMS, "Information Systems");
Set<DepartmentList> keySet = enumMap.keySet();
for (DepartmentList department : keySet) {
String value = enumMap.get(department);
System.out.println("ENUMMAP VALUE:"+value);
}
}
}
Employee class:
public class Employee {
String empName;
int empAge;
DepartmentList empDept;
Employee() {
}
public String getName() {
return empName;
}
public void setName(String name) {
this.empName = name;
}
public int getAge() {
return empAge;
}
public void setAge(int age) {
this.empAge = age;
}
public DepartmentList getDepartment() {
return empDept;
}
public void setDepartment(DepartmentList department) {
this.empDept = department;
}
public Employee(String empName, int empAge, DepartmentList empDept){
}
}
I also have a Department class, but it's currently empty.
Am I on the right track? Can someone give me a nudge? Thank you!

Don't hard-code the data inside the Java program. Put the data in a file and write methods to load the data.
If you MUST hardcode the data in the program, use something like this sample:
public class Employee
{
String name;
int age;
public Employee(String name, int age)
{
this.name = name;
this.age = age;
}
// getters, setters, etc.
}
In the main program
private static Employee[] empData =
{
new Employee("John Smith", 50),
new Employee("Fred Jones", 25),
.
.
.
};
Now you have a static array of Employee objects that you can "load" into your data structure.

If you're asking if there is something like a property in Java, no, there isn't (at least not yet).
If you're asking how to populate your objects something like an IOC container, like Spring, would be a better choice.
Now as it comes to your code you have two main methods in two different classes. Only one will be called. If you want to create a static instance you will be better do
static Employee one = new Employee("Counting Guru", 55, DepartmentList.ACCOUNTING);
or
static Employee one = new Employee();
static {
one.setName("Counting Guru");
one.setAge(55);
one.setDepartment(DepartmentList.ACCOUNTING);
}
When it comes to the enum then you'll better define a constructor for it
public enum DepartmentList {
ACCOUNTING("Accounting"), MARKETING("Marketing");
private String displayName;
public DepartmentList(String displayName) {
this.displayName = displayName;
}
public String getDisplayName() {
return diplayName;
}
}
In the Employee constructor you need to assign the field values to the ones received as arguments.

String Array object in Java

I am trying to print the first element on the two arrays in my Athlete class, country and name. I also need to create a object that simulates three dive attemps an athlete had (that is initially set to zero). I am new to OOP and I dont know how to go abouts doing this in my main... as far as constructors go. This is what i have done so far...
this is the main:
import java.util.Random;
import java.util.List;
public class Assignment1 {
public static void main(String[] args) {
Athlete art = new Athlete(name[0], country[0], performance[0]);
}
}
I just really am not sure what to do...
And this is the class with the arrays.
import java.util.Random;
import java.util.List;
public class Athlete {
public String[] name = {"Art", "Dan", "Jen"};
public String[] country = {"Canada", "Germant", "USA"};
//Here i would like to create something that would be representing 3 dive attemps (that relate to dive and score. eventually.)
Athlete(String[] name, String[] country, Performance[] performance) {
this.name = name;
this.country=country;
this.performance=performance;
}
public Performance Perform(Dive dive){
dive.getDiveName();
return null;
}
public String[] getName() {
return name;
}
public void setName(String[] name) {
this.name = name;
}
public String[] getCountry() {
return country;
}
public void setCountry(String[] country) {
this.country = country;
}
}
thanks in advance for any help and input!
btw there is other classes too, just not relevant atm..

First, as for your Athlete class, you can remove your Getter and Setter methods since you have declared your instance variables with an access modifier of public. You can access the variables via <ClassName>.<variableName>.
However, if you really want to use that Getter and Setter, change the public modifier to private instead.
Second, for the constructor, you're trying to do a simple technique called shadowing. Shadowing is when you have a method having a parameter with the same name as the declared variable. This is an example of shadowing:
----------Shadowing sample----------
You have the following class:
public String name;
public Person(String name){
this.name = name; // This is Shadowing
}
In your main method for example, you instantiate the Person class as follow:
Person person = new Person("theolc");
Variable name will be equal to "theolc".
----------End of shadowing----------
Let's go back to your question, if you just want to print the first element with your current code, you may remove the Getter and Setter. Remove your parameters on your constructor.
public class Athlete {
public String[] name = {"Art", "Dan", "Jen"};
public String[] country = {"Canada", "Germany", "USA"};
public Athlete() {
}
In your main method, you could do this.
public static void main(String[] args) {
Athlete art = new Athlete();
System.out.println(art.name[0]);
System.out.println(art.country[0]);
}
}

Currently you can't access the arrays named name and country, because they are member variables of your Athelete class.
Based on what it looks like you're trying to do, this will not work.
These arrays belong in your main class.

Your attempt at an athlete class seems to be dealing with a group of athletes, which is a design fault.
Define a class to represent a single athlete, with fields that represent the athlete's attributes:
public class Athlete {
private final String name;
private final String country;
private List<Performance> performances = new ArrayList<Performance>();
// other fields as required
public Athlete (String name, String country) {
this.name = name;
this.country = country;
}
// getters omitted
public List<Performance> getPerformances() {
return performances;
}
public Performance perform(Dive dive) {
// not sure what your intention is here, but something like this:
Performance p = new Performance(dive, this);
// add new performance to list
performances.add(p);
return p;
}
}
Then your main method would use ti like this:
public class Assignment1 {
public static void main(String[] args) {
String[] name = {"Art", "Dan", "Jen"};
String[] country = {"Canada", "Germant", "USA"};
Dive[] dive = new Dive[]{new Dive("somersault"), new Dive("foo"), new Dive("bar")};
for (int i = 0; i < name.length; i++) {
Athlete athlete = new Athlete(name[i], country[i]);
Performance performance = athlete.perform(dive[i]);
// do something with athlete and/or performance
}
}
}

I think you are a little messed up with what you doing.
Athlete is an object, athlete has a name, i has a city where he lives.
Athlete can dive.
public class Athlete {
private String name;
private String city;
public Athlete (String name, String city){
this.name = name;
this.city = city;
}
--create method dive, (i am not sure what exactly i has to do)
public void dive (){}
}
public class Main{
public static void main (String [] args){
String name = in.next(); //enter name from keyboad
String city = in.next(); //enter city form keybord
--create a new object athlete and pass paramenters name and city into the object
Athlete a = new Athlete (name, city);
}
}

public static void main(String[] args) {
public String[] name = {"Art", "Dan", "Jen"};
public String[] country = {"Canada", "Germant", "USA"};
// initialize your performance array here too.
//Your constructor takes arrays as an argument so you need to be sure to pass in the arrays and not just objects.
Athlete art = new Athlete(name, country, performance);
}

First off, the arrays are pointless, let's get rid of them: all they are doing is providing values for mock data. How you construct mock objects has been debated ad nauseum, but clearly, the code to create the fake Athletes should be inside of a unit test. I would use Joshua Bloch's static builder for the Athlete class, but you only have two attributes right now, so just pass those in a Constructor. Would look like this:
class Athlete {
private String name;
private String country;
private List<Dive> dives;
public Athlete(String name, String country){
this.name = name;
this.country = country;
}
public String getName(){
return this.name;
}
public String getCountry(){
return this.country;
}
public String getDives(){
return this.dives;
}
public void addDive(Dive dive){
this.dives.add(dive);
}
}
Then for the Dive class:
class Dive {
private Athlete athlete;
private Date date;
private double score;
public Dive(Athlete athlete, double score){
this.athlete = athlete;
this.score = score;
this.date = new Date();
}
public Athlete getAthlete(){
return this.athlete;
}
public Athlete getAthlete(){
return this.athlete;
}
public Athlete getAthlete(){
return this.athlete;
}
}
Then make a unit test and just construct the classes, and manipulate them, make sure that they are working. Right now they don't do anything so all you could do is assert that they are retaining the Dives that you are putting in them. Example:
#Test
public void testThatDivesRetainInformation(){
Athlete art = new Athlete("Art", "Canada");
Dive art1 = new Dive(art, 8.5);
Dive art2 = new Dive(art, 8.0);
Dive art3 = new Dive(art, 8.8);
Dive art4 = new Dive(art, 9.2);
assertThat(art.getDives().size(), is(5));
}
Then you could go through and add tests for things like, making sure that you can't construct a dive without an athlete, etc.
You could move construction of the athletes into the setup method of the test so you could use it all over the place. Most IDEs have support for doing that with a refactoring.