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How can we create an instance for a nested class in array of objects in java?

import java.util.Arrays;
import java.util.Scanner;
public class employee{
public String name;
public class employee_address{
String street_name;
String city;
String zipcode;
String state;
String country;
}
public static void main(String []args){
Scanner user_input = new Scanner(System.in);
int no_of_employees = user_input.nextInt();
employee[] employees_list = new employee[no_of_employees];
for(int i = 0;i < no_of_employees;i++){
employees_list[i].name = user_input.nextLine();
employees_list[I].employee_address = // this is it ?
}
}
}
In the code above I do understand that the employee_address is a class and can't be accessed
directly without an instance being created like in the code, that makes no sense. but how can I create an instance of the employee_address class that is associate with each employee.
like in the code above 'employee_address' is associated with every employee but how can the class 'employee_address' be initialised and how can I set the street_name, city and the rest of the members in the address class. any ideas would be appreciated.

You can't directly create an instance of inner class, the reason because since it is the property of another instance we always need to use it though the instance of parent variable.
Let's say you have a class, which have two propeties:
public class Employee {
public String name;
public EmployeeAddress emAddress;
}
to access emAddress you need to use through the instance of Employee class, for example -
Employee object = new Employee();
EmployeeAddress empAdd = object.new EmployeeAddress();
Full code:
public class Employee {
public String name;
public EmployeeAddress emAddress;
public class EmployeeAddress {
String street_name;
String city;
String zipcode;
String state;
String country;
public String getStreet_name() {
return street_name;
}
public void setStreet_name(String street_name) {
this.street_name = street_name;
}
public String getCity() {
return city;
}
public void setCity(String city) {
this.city = city;
}
public String getZipcode() {
return zipcode;
}
public void setZipcode(String zipcode) {
this.zipcode = zipcode;
}
public String getState() {
return state;
}
public void setState(String state) {
this.state = state;
}
public String getCountry() {
return country;
}
public void setCountry(String country) {
this.country = country;
}
#Override
public String toString() {
return "EmployeeAddress [street_name=" + street_name + ", city=" + city + ", zipcode=" + zipcode
+ ", state=" + state + ", country=" + country + "]";
}
}
public static void main(String[] args) {
Scanner user_input = new Scanner(System.in);
int no_of_employees = user_input.nextInt(); // let's say no_of_employees = 1
Employee[] employees = new Employee[no_of_employees];
for (int i = 0; i < no_of_employees; i++) {
Employee object = new Employee();
object.setName("Virat Kohli");
EmployeeAddress empAdd = object.new EmployeeAddress();
empAdd.setCity("New Delhi");
empAdd.setCountry("India");
empAdd.setState("Delhi");
empAdd.setStreet_name("Chandni Chalk");
empAdd.setZipcode("741124");
object.setEmAddress(emAddress);
employees[i] = object;
}
System.out.println(employees[0]);
user_input.close();
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public EmployeeAddress getEmAddress() {
return emAddress;
}
#Override
public String toString() {
return "Employee [name=" + name + ", emAddress=" + emAddress + "]";
}
public void setEmAddress(EmployeeAddress emAddress) {
this.emAddress = emAddress;
}
}
I have modified your code to sonar standard.

Below code uses Java naming conventions (which your code does not).
Notes after the code.
import java.util.Scanner;
public class Employee {
private String name;
private EmployeeAddress address;
public class EmployeeAddress {
String streetName;
String city;
String zipcode;
String state;
String country;
}
public static void main(String[] args) {
Scanner userInput = new Scanner(System.in);
int noOfEmployees = userInput.nextInt();
Employee[] employeesList = new Employee[noOfEmployees];
for (int i = 0; i < noOfEmployees; i++) {
employeesList[i] = new Employee();
employeesList[i].name = userInput.nextLine();
EmployeeAddress employeeAddress = employeesList[i].new EmployeeAddress();
employeesList[i].address = employeeAddress;
employeesList[i].address.streetName = userInput.nextLine();
}
}
}
An inner class is a normal class. It is not a member of its enclosing class. If you want class Employee to have an [employee] address, as well as a [employee] name, you need to add another member variable to class Employee whose type is EmployeeAdress.
Employee[] employeesList = new Employee[noOfEmployees];
The above line creates an array but every element in the array is null. Hence you need to first create a Employee object and assign it to an element of the array. Hence the following line in my code, above:
employeesList[i] = new Employee();
Since EmployeeAddress is not a static class, in order to create a new instance, you first need an instance of the enclosing class, i.e. Employee. Hence the following line in the above code.
EmployeeAddress employeeAddress = employeesList[i].new EmployeeAddress();
Since all your code is in class Employee, in method main you can directly access the members of both class Employee and EmployeeAddress. Nonetheless you need to be aware of the different access modifiers in java.

A few hints:
stick to naming conventions: class names in Java start with capital letters
use (class) definitions before using them (collect them at the top if not inconventient)
if you are sure you want to use inner classes, set them static, unless you want them to be entangled in generics.
Usually normal classes in each their own file are a lot more flexible and far easier to use
if you use objects that only carry public data, try to use final keyword and initialize them ASAP
use proper objects first, and after finishing them assign them to arrays. avan better would be the use of ArrayList and the like
if Employee contains EmployeeAddress, it should initialize it if conventient. so an object is always responsible for its own stuff
Use try/resrouce/catch
scanner.nextInt() can be problematic with newline/line breaks. For user input better readLine() and parse input
Code:
import java.io.PrintStream;
import java.util.ArrayList;
import java.util.Scanner;
public class Employee {
static public class EmployeeAddress {
public final String street_name;
public final String city;
public final String zipcode;
public final String state;
public final String country;
public EmployeeAddress(final Scanner pScanner, final PrintStream pOutPS) {
street_name = readLine(pScanner, pOutPS, "Please enter Street Name:");
city = readLine(pScanner, pOutPS, "Please enter City Name:");
zipcode = readLine(pScanner, pOutPS, "Please enter Zip Code:");
state = readLine(pScanner, pOutPS, "Please enter State:");
country = readLine(pScanner, pOutPS, "Please enter Country:");
}
}
static public String readLine(final Scanner pScanner, final PrintStream pOutPS, final String pPrompt) {
pOutPS.print(pPrompt);
final String value = pScanner.nextLine();
pOutPS.println();
return value;
}
static public int readInt(final Scanner pScanner, final PrintStream pOutPS, final String pPrompt) {
return Integer.parseInt(readLine(pScanner, pOutPS, pPrompt));
}
public final String name;
public final EmployeeAddress address;
public Employee(final Scanner pScanner, final PrintStream pOutPS) {
name = readLine(pScanner, pOutPS, "Please enter Employee Name: ");
System.out.println("Name: " + name);
address = new EmployeeAddress(pScanner, pOutPS);
}
public static void main(final String[] args) {
try (final Scanner user_input = new Scanner(System.in);
final PrintStream output = System.out;) {
final int no_of_employees = readInt(user_input, output, "Please enter number of users: ");
final Employee[] employees_list = new Employee[no_of_employees]; // either this line
final ArrayList<Employee> employees = new ArrayList<>(); // or this line
for (int i = 0; i < no_of_employees; i++) {
output.println("Creating user #" + (i + 1) + "...");
final Employee newEmployeeWithAddress = new Employee(user_input, output);
employees_list[i] = newEmployeeWithAddress; // either this line
employees.add(newEmployeeWithAddress); // or this line
}
}
}
}

Calling methods from different classes | Java

I'm writing code for an application that keeps track of a student’s food purchases at a campus cafeteria. There's two classes - Student, which holds overloaded constructors & appropriate getter & setter methods; and MealCard, which holds a class variable to track the number of meal cards issued, appropriate getter & setter methods, a purchaseItem() method, a purchasePoints() method & an overriddden toString() method. There's a Tester class also.
In my MealCard class, the methods are written but in the Tester when I call them, they don't work correctly. I want to get the itemValue from the user but how do I do this in the MealCard class?
Same goes for the purchasePoints method, how do I get the topUpValue from user in MealCard class?
Code so far is:
public class Student {
// Instance Variables
private String name;
private int age;
private String address;
// Default Constructor
public Student() {
this("Not Given", 0, "Not Given");
}
// Parameterized constructor that takes in values
public Student(String name, int age, String address) {
this.name = name;
this.age = age;
this.address = address;
}
// Getters and Setters
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public int getAge() {
return age;
}
public void setAge(int age) {
this.age = age;
}
public String getAddress(){
return address;
}
public void setAddress(String address) {
this.address = address;
}
// toString() to be overriden
#Override
public String toString() {
return "Name: " + this.name + "\n" + "Age: " + this.age + "\n" + "Address: " + this.address;
}
}
`
public class MealCard extends Student {
static int numberOfMealCards;
private final static int DEFAULT_BALANCE = 1000;
private int itemValue;
private int topUpValue;
public int newBalance;
// Getters and Setters
public int getItemValue() {
return itemValue;
}
public void setItemValue(int itemValue) {
this.itemValue = itemValue;
}
public int getTopUpValue() {
return topUpValue;
}
public void setTopUpValue(int topUpValue) {
this.topUpValue = topUpValue;
}
// purchaseItem method for when students buy food
public int purchaseItem() {
newBalance = DEFAULT_BALANCE - itemValue;
return newBalance;
}
// purchasePoints method for students topping up their meal card balance
public int purchasePoints() {
newBalance = DEFAULT_BALANCE + topUpValue;
return newBalance;
}
// Overriden toString method
#Override
public String toString() {
return super.toString() + "Meal Card Balance: " + this.newBalance + "\n" + "Number of Meal Cards: " + numberOfMealCards;
}
}
`
import java.util.Scanner;
public class TestMealCard {
public static void main(String[] args) {
// Create instances of MealCard class
MealCard student1 = new MealCard();
MealCard student2 = new MealCard();
Scanner keyboard = new Scanner(System.in);
System.out.println("Name: ");
student1.setName(keyboard.nextLine());
System.out.println("Age: ");
student1.setAge(keyboard.nextInt());
System.out.println("Address: ");
student1.setAddress(keyboard.nextLine());
System.out.println("Meal Card Balace: ");
student1.newBalance = keyboard.nextInt();
System.out.println("Number of Meal Cards Issued: ");
student1.numberOfMealCards = keyboard.nextInt();
System.out.println("Name: ");
student2.setName(keyboard.nextLine());
System.out.println("Age: ");
student2.setAge(keyboard.nextInt());
System.out.println("Address: ");
student2.setAddress(keyboard.nextLine());
System.out.println("Meal Card Balace: ");
student2.newBalance = keyboard.nextInt();
System.out.println("Number of Meal Cards Issued: ");
student2.numberOfMealCards = keyboard.nextInt();
// Call purchaseItem
student1.purchaseItem();
// Call purchasePoints
student2.purchasePoints();
// Call tString to output information to user
}
}

In order to set the itemValue from the user you need to get get that input from the user using this setItemValue() method.
Ex.
System.out.print("Please enter the item value: ");
student1.setItemValue(keyboard.nextInt());
or
int itemVal = 0;
System.out.print("Please enter the item value: ");
itemVal = keyboard.nextInt();
student1.setItemValue(itemVal);
as for the other method call just call the setter for toUpValue.
Ex.
System.out.print("Please enter the item value: ");
student1.setTopUpValue(keyboard.nextInt());
or
int toUpVal = 0;
System.out.print("Please enter the item value: ");
itemVal = keyboard.nextInt();
student1.setTopUpValue(topUpVal);
Hope that helps =).

How to test default constructor in a different class in Java

How do you test a default constructor in one class and then test it in a different class?
This is the code for the Person class which has the default constructor.
I'm not sure in the PersonTester class how to access this default constructor and how to test it - what I have so far for the second class is also below.
Any help will be muchly appreciated, thanks :)
class Person {
// Data Members
private String name; // The name of this person
private int age; // The age of this person
private char gender; // The gender of this person
// Default constructor
public Person() {
name = "Not Given";
age = 0;
gender = 'U';
}
// Constructs a new Person with passed name, age, and gender parameters.
public Person(String personName, int personAge, char personGender) {
name = personName;
age = personAge;
gender = personGender;
}
// Returns the age of this person.
public int getAge( ) {
return age;
}
// Returns the gender of this person.
public char getGender( ) {
return gender;
}
// Returns the name of this person.
public String getName( ) {
return name;
}
// Sets the age of this person.
public void setAge( int personAge ) {
age = personAge;
}
// Sets the gender of this person.
public void setGender( char personGender ) {
gender = personGender;
}
// Sets the name of this person.
public void setName( String personName ) {
name = personName;
}
} // end class
import java.util.Scanner;
public class PersonTester {
// Main method
public static void main(String[] args){
// TEST THE DEFAULT CONSTRUCTOR FIRSTLY.
// Create an instance of the Person class.
Person person1 = new Person();
Scanner input = new Scanner(System.in);
// Get the values from user for first instance of Person class.
System.out.println("Person 1 Name: ");
person1.setName(input.nextLine());
System.out.println("Person 1 Age: ");
person1.setAge(input.nextInt());
System.out.println("Person 1 Gender: ");
person1.setGender(input.next().charAt(0););
// Alternatively assign values to the Person class.
// person1.setName("Not Given");
// person1.setAge(0);
// person1.setGender("U");
}
}

Your test would look like:
#Test
public void testDefaultConsturctor(){
Person person = new Person();
Assert.assertEquals(person.getName(),"Not Given");
Assert.assertEquals(person.getAge(),0);
Assert.assertEquals(person.getGender(),'U');
}

You can test default constructor in the second class without using asserts with this code
Person defaultPerson = new Person();
System.out.print("My default name is: " + defaultPerson.getName());
System.out.print("My default age is: " + defaultPerson.getAge());
System.out.print("My default gender is: " + defaultPerson.getGender());
By the way, I don´t know what´s the problem, because you are calling default constructor in your second class (PersonTester)

Java Inheritance of Classes

I am trying to figure out Inheritance and Arrays in Java and I am trying to get these classes to work together. I believe I have the Inheritance down, but I am still struggling with the array part.
There are three files: 1. Person.java -base class 2. Student.java -a derived class of Person.java 3. Family.java -not quite sure, I think it's its own base class
Person.java has two instance variables, String name and int age, and an assortment of constructors, toString, equals, and set/get methods
Student.java, again, a derived class of Person, by definition will have all the stuff contained within Person, as well as two more instance vars, String major, and double gpa. This class also have get/set methods for major and gpa, an equals method that compares one class student with another class student, and I believe it's called an overidden method of toString that returns name, age, major, and gpa all in one string.
Lastly, Family.java is where the main method resides. It creates an array of type Person, adds "Persons" to this array, then outputs them.
I am getting an error that says: "main" java.lang.ArrayIndexOutOfBoundsException: 8
I can not figure out why this program is not working properly and would appreciate any help to figure this out. Thank you.
Person.java Class
public class Person
{
private String name;
private int age;
public Person()
{
name = "John Smith";
age = 1;
}
public Person(String n, int a)
{
name = n;
age = a;
}
public String toString()
{
return ("Name: " + getName() + ", Age: " + age + " ");
}
public boolean equals(Person otherPerson)
{
return (getName().equals(otherPerson.getName()) && (age == otherPerson.age));
}
public String getName()
{
return name;
}
public void setName(String newName)
{
name = newName;
}
public int getAge()
{
return age;
}
public void setAge(int newAge)
{
age = newAge;
}
}
Student.java Class
public class Student extends Person
{
private String major;
private double gpa;
public Student()
{
super();
major = "Undecided";
gpa = 0.0;
}
public Student(String theName, int theAge, String theMajor, double theGpa)
{
super(theName, theAge);
setMajor(theMajor);
setGpa(theGpa);
}
public String toString()
{
return ("Name: " + getName() + ", Age: " + getAge() + ", Major: " + major + ", GPA: " + gpa);
}
public boolean equals(Student otherStudent)
{
return (major.equals(otherStudent.major) && (gpa == otherStudent.gpa));
}
public String getMajor()
{
return major;
}
public void setMajor(String newMajor)
{
major = newMajor;
}
public double getGpa()
{
return gpa;
}
public void setGpa(double newGpa)
{
gpa = newGpa;
}
}
Family.java Class
public class Family
{
private int famArray = 0;
private Person[] family;
public Family(int size_of_family)
{
famArray = size_of_family;
family = new Person[famArray];
}
public void addPerson(Person p)
{
boolean isPresent = false;
int i;
for(i = 0; i < family.length; i++)
{
if(family[i] != null && family[i].equals(p))
{
isPresent = true;
System.out.println(p.getName() +
" is already present in the family");
}
}
if(isPresent == false)
family[i] = p;
}
public void printOutFamily()
{
for(int i = 0; i < family.length; i++)
{
System.out.println(family[i].toString());
}
}
public static void main(String[] args)
{
Family f = new Family(8);
Person fred= new Person("Fred Flintstone", 50);
System.out.println("created " + fred);
f.addPerson(fred);
f.addPerson(fred);
Student fredStudent = new Student("Fred Flintstone", 50, "Math", 3.1);
System.out.println("created "+ fredStudent);
f.addPerson(fredStudent);
Person wilma = new Person("Wilma Flintstone", 48);
f.addPerson(wilma);
Student george= new Student("George", 21, "Politics", 3.1);
System.out.println("created " + george);
f.addPerson(george);
george.setName("Georgie");
f.addPerson(new Student("George", 21, "Politics", 3.1));
f.addPerson(new Student("John", 18, "Geology", 2.9));
f.addPerson(new Student("Jane", 21, "Music", 3.2));
f.addPerson(new Student("Tarzan", 22, "Gymnastics", 4.0));
f.addPerson(new Student("Jim", 21, "Physics", 2.5));
System.out.println("****** family listing: ");
f.printOutFamily();
}
}

Here's the problem, in Family#addPerson method:
if(isPresent == false)
family[i] = p;
You're adding the element in position i. If the element is not found, then i value will be family.length, thus giving you the exception.
Use int famArray field instead:
if(isPresent == false) {
family[famArray++] = p;
}
Or in an easier way for starters:
if(isPresent == false) {
family[famArray] = p;
famArray = famArray + 1;
}
As an addition to your current problem, you should first check if the famArray element is equals to family.length. If they're the same, then increase the array or do not allow more elements.
You state you have the same problem. This is because you're initializing famArray with the length of the array, noted in Family class constructor:
public Family(int size_of_family) {
famArray = size_of_family; //here
family = new Person[famArray];
}
Change the code to:
public Family(int size_of_family) {
famArray = 0;
family = new Person[size_of_family];
}
And you're done.

The problem is the line
family[i] = p;
This occurs after a for loop which increments i to be equal to the length of the array. I don't have any suggestions to fix it because I'm not sure what you are trying to do here.

Passing a comma delimited string into a class [closed]

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Here is what I have so far in my code
public class Person {
public Person()
{
String person = "";
int age = 0;
String city = "";
int sibCount = 0;
// make an instance field for name, city, age, and siblingCount
Person person = new Person();
Person age = new Person();
Person city = new Person();
Person sibCount = new Person();
}
// make a method called parseCommaDelim
public void parseCommaDelim(String[] args){
// return a Person instance UNSURE HERE
}
// make a toString method
public String toString()
{
String str = "person" + person + "age" + age + "city" + city;
return str;
}
}
}
I am trying return a person instance and I am not sure how to do it. I tried 'return Person;' and my code did not like it.
My toString method is not working either because it does not know what person, age, or city is, and I am not sure why.

What you want to achieve is probably something along the following lines:
public class Person {
// fields
private String person = "";
private int age = 0;
private String city = "";
private int sibCount = 0;
// constructor
public Person() {
}
// public access methods (getters)
public String getPerson() {
return this.person;
}
public int getAge() {
return this.age;
}
public String getCity() {
return this.city;
}
public int getSibCount() {
return this.sibCount;
}
// toString
public String toString() {
return "person: " + person + ", age: " + age + ", city: " + city;
// factory method
public static Person parseCommaDelim(String s) {
String[] tokens = s.split(",");
Person instance = new Person();
instance.person = tokens[0];
instance.age = Integer.parseInt(tokens[1];
instance.city = tokens[2];
// ...
return instance;
}
}
The field person should probably renamed to name. Depending wether you want to make your class immutable or not you may want to add either a constructor which takes all parameters as parameters:
public Person(String name, int age, String city, int sibCount) {
this.name = name;
this.age = age;
this.city = city;
this.sibCount = sibCount;
}
or add setters for the changable fields, for example:
public void setCity(String city) {
this.city = city;
}
btw. with above constructor you could modify the factory to the following slightly cleaner code:
public static Person parseCommaDelim(String s) {
String[] tokens = s.split(",");
String person = tokens[0];
int age = Integer.parseInt(tokens[1];
String city = tokens[2];
int sibCount = Integer.parseInt(tokens[3]);
return new Person(person, age, city, sibCount);
}

public class Person {
public String person;
public int age;
public String city;
public int sibCount;
public Person()
{
person = "";
age = 0;
city = "";
sibCount = 0;
}
// make a method called parseCommaDelim
public String parseCommaDelim(String[] args){
// return a Person instance UNSURE HERE
}
// make a toString method
public String toString()
{
String str = "person" + person + "age" + age + "city" + city;
return str;
}
}