We Keep Coding

How to create an empty array in constructor java

I have a homework where I created 2 classes. TeamMember and ProjectTeam. However I have a problem with creating an empty array of type TeamMember.
class TeamMember {
protected String name;
protected ProjectTeam team;
TeamMember(String newName, ProjectTeam newTeam){
name = newName;
team = newTeam;
}
class ProjectTeam {
protected String name;
protected TeamMember[] members;
public ProjectTeam(String newName){
name = newName;
members = help here;
}
public class Main {
public static void main(String[] args) {
ProjectTeam team1 = new ProjectTeam("team1");
TeamMember peter = new TeamMember("Peter", team1);
System.out.println(peter.name);
System.out.println(team1.members);
}
}
What I am trying to do is to create a TeamMember and pass it to a ProjectTeam. However I cant seem to find a way how to pass an empty array of type Team Member in construcor of ProjectTeam. Any feedback would be appreciated.

As the comments say, maybe you should model this differently, especially if you need to add/remove elements, but here is how you create a zero-length array. Sometimes, rarely, you need that. It's the same as any other length:
String[] myArray = new String[0];
Alternatively:
String[] myArray = new String[]{}; // empty array initializer

try to used ArrayList to the connection between the TeamMember and ProjectTeam
class TeamMember {
protected String name;
protected ProjectTeam team;
TeamMember(String newName, ProjectTeam newTeam){
name = this.newName;
team = this.newTeam;
}
class ProjectTeam {
protected String name;
protected ArrayList <TeamMember> members;
public ProjectTeam(String newName,ArrayList<TeamMember>members){
name = this.newName;
members =this.members;
}
ProjectTeam team1 = new ProjectTeam("team1");
ArrayList<ProjectTeam> traems=new ArrayList<ProjectTeam>();
traems.add(team1)
check the code I don't know if it works fine or not

How to change array to an object class?

I have cut out the code to shorten the page but I'm asking how do I change personInterests into its own class. Apologies for the vague question but essentially I want to change personInterests in my Person class to a class where personInterests has multiple variables.
import java.util.ArrayList;
import java.util.*;
public class Person{
private String personName;
private String[] personInterests = new String[3];
public Person(String personName, String[] personInterests){
this.personName = personName;
this.personInterests = personInterests;
}
public void setInterests(String[] personInterests){
this.personInterests = personInterests;
}
public String[] getInterests(){
return personInterests;
}
public String getName(){
return personName;
}
public String toString(){
String result = getName() + " ";
for (String interests : personInterests) {
result += interests + " ";
}
return result;
}
}
This was my idea of how it would work just not sure how I would use this class and call it later on.
import java.util.ArrayList;
import java.util.*;
public class Interests {
private int interestDangerRating;
private String interestName;
private ArrayList<Interests> interestsList = new ArrayList<>();
public Interests (int interestDangerRating ,String interestName){
this.interestDangerRating = interestDangerRating;
this.interestName = interestName;
}
public void addInterests(Interests p){
interestsList.add(p);
}
Interests getInterests(int i){
return interestsList.get(i);
}
}
Any help is appreciated, as I said this code has mostly been taken out and this was an old project already completed just wanted to see if I could change some of the features.

OK so here's what I would do to clean this up for you and make it work. Firstly, think about what you are trying to do. You want to create a Person who has multiple Interests, right? So the Interest class, going by your above example, can be changed to be a typical Java object class as follows:
public class Interest {
private int dangerRating;
private String name;
public Interest (int dangerRating, String name) {
this.dangerRating = dangerRating;
this.name = name;
}
public int getDangerRating() {
return dangerRating;
}
public String getName() {
return name;
}
}
So now we've an Interest class set up where you can set a name for your interest and a danger rating. What we need to do, now, is edit your Person class so as you can store a list of interests for each Person you create.
import java.util.ArrayList;
public class Person{
private String name;
private ArrayList<Interest> interests = new ArrayList<Interest>();
public Person(String name, ArrayList<Interest> interests) {
this.name = name;
this.interests = interests;
}
public void addInterest(Interest newInterest) {
interests.add(newInterest);
}
public Interest getInterest(int indexOfInterest) {
return interests.get(indexOfInterest);
}
public ArrayList<Interest> getInterests() {
return interests;
}
public String getName() {
return name;
}
public String toString() {
String result = getName() + " ";
for(Interest interest : interests) {
result += interest.getName() + "(" + interest.getDangerRating() + ")" + " ";
}
return result.trim();
}
}
This allows you to set an initial list of all interests for your new Person and, from there, you can add new interests, get all interests or get any individual interest.
Hope this helps to clarify for you how this should all fit together!
So now it's time to instantiate everything. Lets create some Interestobjects which we will use:
Interest golf = new Interest(1, "golf");
Interest swimming = new Interest(3, "swimming");
Now lets assume we want two people called John and Mary. John likes golf and swimming while Mary only likes swimming. We'd then create their list of Interest as follows:
ArrayList<Interest> johnsInterests = new ArrayList<Interest>();
johnsInterests.add(golf);
johnsInterests.add(swimming);
ArrayList<Interest> marysInterests = new ArrayList<Interest>();
marysInterests.add(swimming);
And finally, we'd then create our two Person objects which will include the persons name and interests list.
Person john = new Person("John", johnsInterests);
Person mary = new Person("Mary", marysInterests);
And voila!

First, make an Interestclass:
public class Interest {
private int interestDangerRating;
private String interestName;
// .. getters and setters
}
then in the Personclass get rid of private String[] personInterests = new String[3];
and replace it by:
private ArrayList<Interest> interestsList = new ArrayList<>();

You're getting there with the logic of your Interests class, but it needs a few changes
import java.util.ArrayList;
import java.util.*;
public class Interests {
private int interestDangerRating;
// Is this a unique name for the entire class? If yes then no worries, but if not
// then its not needed, you've already got a list of interest names below
private String interestName;
// Change the array list to hold Strings, it's a list of words
private ArrayList<String> interestsList = new ArrayList<>();
public Interests (int interestDangerRating ,String interestName){
this.interestDangerRating = interestDangerRating;
this.interestName = interestName;
}
public void addInterest(String p){ // Again, change this to String
interestsList.add(p);
}
String getInterest(int i){ // Change this to return a String, since we changed the ArrayList above
return interestsList.get(i);
}
}
There's alot more you need to think about with this class too. How do you know how many interests are in the list, should there be a length variable? Or what about a method that returns the entire list of interests rather than just 1?
Also, there's only one interestDangerRating being set in this class; if each interest has a different danger rating, should't you be adding a danger rating for every interest?
In terms of accessing your new class, you'll need to create a class in your code by:
Interests variableName = new Interests(1, "football");
I have randomly chosen '1' and 'football' above, since they are in your Interest class' constructor. The way your class is built, you cannot use it without providing an int and a String when the object is made
Finally, to call methods on your class, you use the variable created above to call its methods:
variableName.addInterest("basketball");
String interest = variableName.getInterest(1);
If you're struggling, I recommend looking at a simple java tutorial online. instatiating java classes and calling their methods like this are fundamental concepts in Java :)

How can I pull variables from one java file to another?

I'm at very early stages of learning java.
I currently have one file which has 900 lines of code, which is not good.
I would like to separate my Java file into separate java files which I could "link"
together in some way.
I used to work a lot with CSS, and there it was insanely easy to pull some stylesheets in with the #import.
Would there be a way to "copy" all variables from a file to a different one, the #import way? If I had my array "p" defined in the separate file, could I just #import this file into my main file in a way where I could just try to print p and it would do it?
Thanks a lot in advance!

You cannot split a single class into several different source files. Each source file in Java corresponds to exactly one class. (A class can contain its own inner classes, but that's an unnecessary distraction at your stage!)
You can arrange things so that a member of one class is visible to members of other classes, by giving it the public or default access modifier.
See In Java, difference between default, public, protected, and private

You will probably want to read up about Object Oriented Programming. There are lots of tutorials on Oracle's website. http://docs.oracle.com/javase/tutorial/java/javaOO/index.html
In your case, you can split your classes up to store your array in one class and access it from another class. Something like this:
Here's the class that contains the array:
public class ClassA
{
public int [] arr = {1,2,3,4};
public int [] getArr()
{
return arr;
}
}
Here's the class that accesses the array:
public class ClassB
{
public void printArray(ClassA classB)
{
// access the array through a "getter" (recommended)
System.out.println(Arrays.toString(classB.getArr()));
// you can also access the array directly since it is a public variable
System.out.println(Arrays.toString(classB.arr));
}
public static void main(String [] args)
{
ClassB a = new ClassB();
ClassA b = new ClassA();
a.printArray(b);
}
}
If your classes are in different packages, you include an import statement at the top of the file like:
import packageName.ClassA;

You might want to consider splitting the class if you think it has low cohesion. Take a look at SOLID
Some of the principles listed here might help you break down the class in to smaller manageable highly cohesive units.

I imagine you have something like this currently where everything is in one big class:
public class Main1 {
private String street;
private String city;
public Main1(String street, String city) {
this.street = street;
this.city = city;
}
private void printAddress() {
System.out.println(street);
System.out.println(city);
}
public static void main(String[] args) {
Main1 ex = new Main1("1 Main street", "Springfield");
ex.printAddress();
}
}
As a first step I would move some of the data out of your class into another class, grouping like data together (in this case it's obviously an Address) and then reference that class in your original class, maybe:
class Address {
private String street;
private String city;
public Address(String street, String city) {
this.street = street;
this.city = city;
}
public String getCity() {
return city;
}
public String getStreet() {
return street;
}
}
public class Main {
private void printAddress(Address address) {
System.out.println(address.getStreet());
System.out.println(address.getCity());
}
public static void main(String[] args) {
Main ex = new Main();
Address address = new Address("1 Main street", "Springfield");
ex.printAddress(address);
}
}
After that you might notice that some of the functionality might also logically belong on the class you just pulled out and you can provide methods on the new class to provide that functionality:
class Address {
private String street;
private String city;
public Address(String street, String city) {
this.street = street;
this.city = city;
}
public String formattedAddress() {
return street + "\n" + city;
}
}
public class Main {
public static void main(String[] args) {
Main ex = new Main();
Address address = new Address("1 Main street", "Springfield");
System.out.println(address.formattedAddress());
//ex.printAddress(address);
}
}

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.

Calling a non-static method in a seperate class to a main program

I have a Java program where I have a main class and another class called Person (that makes a 'person' class) with 2 methods. The methods are non-static and are called getName and getAge that stores this info a person element of an ArrayList.
How do I call these in the main program? I know I have to declare an instance of the class but I'm still not sure how to actually do it.

Considering Person a Class with 2 methods:
public class Person{
private String mName;
private int mAge;
public Person(String name, String age){
this.mName = name;
this.mAge = age;
}
//If you want this class to be Immutable please remove the setter methods()//
public void setName(String name){
this.mName = name;
}
public void setAge(String age){
this.mAge = age;
}
public String getName(){
return this.mName ;
}
public String getAge(){
return this.mAge ;
}
}
The Class containing main() method:
public class TestMain{
public static ArrayList<Person> aList = new ArrayList<Person>();
public static void main(String[] args){
Person person1 = new Person("Vivek",26);
Person person2 = new Person("Vicky",27);
aList.add(person1);
aList.add(person2);
}
}

In your main code you can do something like:
Person p = new Person();
p.setName("Jericho Jones");
p.setAge(153);
Of course, it's impossible to tell exactly without seeing the Person class.

You need to instantiate an object for this class.
Person p = new Person();
p.getName()....