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Variable cannot be resolved error in Java

I know this is a very very common error but I am stuck on this one and I totally don't understand why is it happening.
Here is a part of my code
import java.util.ArrayList;
import java.util.Scanner;
public class Manager {
private static Scanner sc = new Scanner(System.in);
protected static ArrayList<String> identifications = new ArrayList<String>();
protected static String[] signIn() {
System.out.println("Hi !");
System.out.println("Welcome to School Management System");
System.out.print("Please enter your ID number : ");
boolean idValid = false;
String providedID = null;
int idListPosition = -1;
do {
try {
providedID = sc.nextLine();
} catch (Exception e) {
System.out.println("Sorry there was an error. Please try again");
System.out.print("Please enter your ID number : ");
}
} while (providedID == null);
while (idValid != true) {
for (String element : identifications) {
if (element.equals(providedID)) {
idValid = true;
idListPosition = identifications.indexOf(element);
break;
}
}
if (idValid && idListPosition != -1) {
System.out.println("Welcome !");
String[] returnValue = {"true", identifications.get(idListPosition), identifications.get(idListPosition + 1), identifications.get(idListPosition + 2)};
return (returnValue);
} else {
System.out.println("Error : the ID you entered does not exist. Please try again");
providedID = null;
do {
try {
providedID = sc.nextLine();
} catch (Exception e) {
System.out.println("Sorry there was an error. Please try again");
System.out.print("Please enter your ID number : ");
}
} while (providedID == null);
}
}
}
public static void main(String[] args) {
init();
String[] response = signIn();
if (response[2].equals("teacher")) {
Teacher user = new Teacher(response[1], response[2], response[3]);
}
if (response[2].equals("student")) {
Student user = new Student(response[1], response[2], response[3]);
}
System.out.println(user);
while(true) {
System.out.println("For help type in help");
System.out.print("Enter a command : ");
String commandWanted = sc.nextLine();
if (commandWanted.equals("info")) user.showInfos();
}
}
protected static void init() {
identifications.add("056789");
identifications.add("teacher");
identifications.add("Temperson");
}
}
The Teacher and Student classes are empty for now. I just made them use the super constructor of their parent class Person :
public class Person {
String type;
String name;
String idNumber;
public Person(String idnumber, String newType, String providedName) {
this.idNumber = idnumber;
this.type = newType;
this.name = providedName;
}
protected String[] showInfos() {
String[] returnValue = {this.type, this.name, this.idNumber};
return returnValue;
}
}
But I get user cannot be resolved to a variable and user cannot be resolved error.
Normally the code that needs user will never run unless sign in has completed. And since sign in never ends before a correct ID is entered, the user variable will always be assigned to a a value.
Thanks for helping !

The scope of the user object is limited to the if condition, hence you are getting this error.
If Teacher and Student extends Person then you can try this piece of code:
public static void main(String[] args) {
init();
String[] response = signIn();
Person user = null;
if (response[2].equals("teacher")) {
user = new Teacher(response[1], response[2], response[3]);
}
if (response[2].equals("student")) {
user = new Student(response[1], response[2], response[3]);
}
System.out.println(user);
while(true) {
System.out.println("For help type in help");
System.out.print("Enter a command : ");
String commandWanted = sc.nextLine();
if (commandWanted.equals("info")) user.showInfos();
}
}

You're having a Scope problem here:
if (response[2].equals("teacher")) {
Teacher user = new Teacher(response[1], response[2], response[3]);
}
if (response[2].equals("student")) {
Student user = new Student(response[1], response[2], response[3]);
}
System.out.println(user);
Variables declared in a if block are local to that if block. You can see this in it's simplest form with an example like this:
if(true) {
String value = "Out of Scope";
}
System.out.println(value); //value cannot be seen outside the if block
You will need to declare your Teacher and/or Student variable outside the if block if you wish to use them after the block (this is where using your inheritance class would come in handy). Using the previous example:
boolean someCondition = true;
String value;
if(someCondition) {
value = "In Scope - True";
} else {
value = "In Scope - False";
}
System.out.println(value); //value can now be seen

You have declared 2 different versions of user, so the print statement can't know which you mean. Or it couldn't if it could see either, but since each is declared inside of its own block, the print doesn't see either of them.

Issues Serializing an ArrayList object containing other ArrayList objects

So I'm Serializing an ArrayList of ArrayLists essentially but I'm running into an issue. To be honest I'm still pretty new to Java, I've tried so many different methods to fix this as well as searched relentlessly on this site and have not been successful. I know that the way I word things may be hard to follow along or is confusing so I'll post my code here to see. Sorry in advance for all the code. SuperUsers has an arraylist of LoginInfo, PasswordKeeper has an Arraylist of SuperUsers, and the SuperUser arraylist gets serialized in PasswordKeeper. but any changes made to the LoginInfo arraylist do not save and i cannot figure out why. If anyone can help I would really Appreciate it. Thanks
public class PasswordKeeper{
private ArrayList<SuperUser> users;
private static Scanner keyboard = new Scanner(System.in);
public PasswordKeeper() {
users = new ArrayList();
}
public void login() {
try {
// reads in SuperUser arraylist
get();
} catch (EOFException a) {
System.out.println("You are the First User!");
} catch (IOException b) {
System.out.println(b);
} catch (ClassNotFoundException c) {
System.out.println(c);
}
boolean loopDisplay = true;
while (loopDisplay) {
existingUser = keyboard.next();
existingPass = keyboard.next();
SuperUser temp = new SuperUser(existingUser, existingPass);
System.out.println();
if (users.contains(temp)) {
// viewing superUser method
temp.display();
//saves after method call is over
try {
System.out.println("Saving.");
save(users);
} catch (IOException e) {
System.out.println(e);
}
}
}
//This happens if there is a new user
if(answer == 2){
SuperUser tempNew = null;
boolean cont = true;
String newUser;
String pass;
while(cont){
newUser = keyboard.nextLine();
System.out.println();
//System.out.println(users.size());
tempNew = new SuperUser(newUser, pass);
if(passValid(pass) == true){
if(makeSure(tempNew) == true){
System.out.println("Login Created!");
tempNew = new SuperUser(newUser, pass);
//actually being added to the arraylist
users.add(tempNew);
cont = false;
}
}
}
//SuperUser.display method
tempNew.display();
try{
System.out.println("Saving.");
save(users);
}catch(IOException e){
System.out.println(e);
}
}
}
}
//makeSure and passValid methods
public boolean makeSure(SuperUser user){
if(users.contains(user)){
return false;
}
return true;
}
public boolean passValid(String pass){
boolean passes = false;
String upper = "(.*[A-Z].*)";
String lower = "(.*[a-z].*)";
String numbers = "(.*[0-9].*)";
String special = "(.*[,~,!,#,#,$,%,^,&,*,(,),-,_,=,+,[,{,],},|,;,:,<,>,/,?].*$)";
if((pass.length()>15) || (pass.length() < 8)){
System.out.println("Entry must contain over 8 characters\n" +
"and less than 15.");
passes = false;
}if(!pass.matches(upper) || !pass.matches(lower)){
System.out.println("Entry must contain at least one uppercase and lowercase");
passes = false;
}if(!pass.matches(numbers)){
System.out.println("Password should contain atleast one number.");
passes = false;
}if(!pass.matches(special)){
System.out.println("Password should contain atleast one special character");
passes = false;
}else{
passes = true;
}
return passes;
//serializable methods
public void save(ArrayList<SuperUser> obj) throws IOException {
File file = new File("userInformation.dat");
FileOutputStream fileOut = new FileOutputStream(file, false);
BufferedOutputStream buffedOutput = new BufferedOutputStream(fileOut);
ObjectOutputStream out = new ObjectOutputStream(buffedOutput);
out.writeObject(obj);
out.close();
fileOut.close();
}
public ArrayList<SuperUser> get() throws IOException, ClassNotFoundException {
FileInputStream fileIn = new FileInputStream("userInformation.dat");
BufferedInputStream buffedInput = new BufferedInputStream(fileIn);
ObjectInputStream in = new ObjectInputStream(buffedInput);
users = (ArrayList<SuperUser>) in.readObject();
in.close();
fileIn.close();
return users;
}
public class SuperUser implements Serializable {
private String userName;
private String password;
private static Scanner keyboard = new Scanner(System.in);
private ArrayList<LoginInfo> info = new ArrayList();
public SuperUser(String name, String pass) {
userName = name;
password = pass;
}
public String getUser() {
return userName;
}
public void display() {
String next = keyboard.next();
//want to add data to LoginInfo arraylist
if (next.equalsIgnoreCase("add")) {
add();
} else if (next.equalsIgnoreCase("delete")) {
delete();
} else if (numberCheck(next)) {
int choice = (int) Integer.parseInt(next) - 1;
edit(choice);
//!!!! this: after doing this i lose whatever data i added
//to the LoginInfo arraylist, right after this the
//SuperUser arraylist gets saved. but the added data to
//loginInfo does not
} else if (next.equalsIgnoreCase("logout")) {
System.out.println(info.size());
}
}
public boolean numberCheck(String in) {
try {
Integer.parseInt(in);
} catch (NumberFormatException e) {
return false;
}
return true;
}
//method to add to the Arraylist
public void add() {
System.out.println("What is the website name?:");
String trash = keyboard.nextLine();
String webName = keyboard.nextLine();
System.out.println("The Username?:");
String webUsername = keyboard.nextLine();
System.out.println("The Password?:");
String webPass = keyboard.nextLine();
info.add(new LoginInfo(webUsername, webPass, webName));
System.out.println(info.size());
//method goes back to display
display();
}
}
}

Your problem is here
SuperUser temp = new SuperUser(existingUser, existingPass);
System.out.println();
if (users.contains(temp)) {
// viewing superUser method
temp.display();
You create a temporary object which with the username and password.
Your 'users.contains()' method returns true because '.equals()' is based on the username, however the 'temp' object is a different instance to that in the list.
So when you call 'temp.display()' it is not calling on an object in the list, so no data changes will save.
You need to find the existing object from the list for that user. I would suggest that you swap your list for a map keyed on username.

You have a list named users. Once you created new SuperUser instance (temp), you are checking that it belongs to this list (users.contains(temp), which is false of course - from where it will occur there?). If it have belonged, the method display would be called, which in turn would add LoginInfo to that SuperUser (add() call), but I bet in reality it doesn't happened.
Also, I see where you read from users (check whether new SuperUser instances belong there), I see where you overwrite it (during desealization) but I don't see adding any instance to there, which makes me think that it is always empty.
Are you sure that SuperUser contains any LoginInfo in its array list?

ArrayList and BufferedReader Note Taking Program

I have created a simple program that takes a title and a note which you enter then you have a choice to export the notes to txt file using BufferedWriter however because each note is a object which is stored in a ArrayList when storing them I iterate through a for enhanced loop it keeps duplicating each note as I iterate through all the object.
Note Class
import java.util.*;
public class Notes
{
private String notes;
private String titleOfNotes;
Scanner input = new Scanner(System.in);
public Notes()
{
titleOfNote(input);
takeNotes(input);
}
public void takeNotes(Scanner x)
{
System.out.println("Please Enter Your Note");
notes = x.nextLine();
}
public void titleOfNote(Scanner y)
{
System.out.println("Please Enter Title");
titleOfNotes = y.nextLine();
}
public String toString()
{
return "Title: " + titleOfNotes + "\t" + notes;
}
}
App Class //Does mostof the Work
import java.util.*;
import java.io.*;
public class App
{
private int exit = 0;
private int createANote;
private int displayTheNotes;
private int inputFromUser;
public boolean haveFileBeenWritten = true;
File file = new File("Notes.txt");
Scanner input = new Scanner(System.in);
ArrayList<Notes> arrayOfNotes = new ArrayList<Notes>();
public void makeNoteObject()
{
arrayOfNotes.add(new Notes());
}
public void displayAllTheNote(ArrayList<Notes> n)
{
for(Notes singleObjectOfNote : n)
{
System.out.println(singleObjectOfNote);
}
}
public void programUI(){
while(exit != 1)
{
System.out.println("1. Create A Note");
System.out.println("2. Display The Notes");
System.out.println("3. Exit");
System.out.println("4. Export to text file");
System.out.println("Enter Your Operation");
inputFromUser = input.nextInt();
if(inputFromUser == 1)
{
makeNoteObject();
}
else if(inputFromUser == 2)
{
displayAllTheNote(arrayOfNotes);
}
else if(inputFromUser == 3)
{
System.out.println("Exited");
exit = 1;
}
else if(inputFromUser == 4)
{
makeATxtFileFromNotes(arrayOfNotes);
System.out.println("Textfile created filename: " + file.toString());
}
else
{
System.out.println("You Select A Invalid Command");
}
}
}
public void makeATxtFileFromNotes(ArrayList<Notes> x)
{
try (BufferedWriter bw = new BufferedWriter(new FileWriter(file,haveFileBeenWritten)))
{
//Problem here!
for(Notes singleObjectOfNotes : x)
{
bw.write(singleObjectOfNotes.toString());
bw.newLine();
}
}catch(IOException e)
{
System.out.println("Cant Write File: " + file.toString());
haveFileBeenWritten = false;
}
}
public App()
{
programUI();
}
public static void main(String[]args)
{
App objectOfApp = new App();
}
}
I am new to Java so my code my not be the best!

If your problem is that you only need to see current list's Notes excluding the previous', it's because of this line:
try (BufferedWriter bw = new BufferedWriter(new FileWriter(file,haveFileBeenWritten)))
By default, haveFileBeenWritten is true so based on the FileWriter API it will APPEND on the existing file Notes.txt so if you don't want that, change it to false.
Parameters:
file - a File object to write to
append - if true, then bytes will be
written to the end of the file rather than the beginning
EDIT: To access List<> elements, use get().
Example:
int size = myList.size();
for (int i = 0 ; i < size ; i++) {
//...
Notes note = myList.get(i);
//...
}

Struggling with objects, program does not work as expected(java)

So I have this cyclingmanager game, and I want to show a list of riders by names, and then I want to show their abilities when the user picks a rider. The program compiles and runs nicely, the problem is in my riders() method.It just does not print out c1, my first rider. Thanks in advance.
import java.util.ArrayList;
import java.util.List;
import java.util.Scanner;
public class CyclingManager2 {
public static void main(String[] args) {
//menyvalgene
Menu m = new Menu();
m.choice();
}
}
class Menu {
Scanner in = new Scanner(System.in);
Cyclist cy = new Cyclist();
//choices
public void choice() {
int choice = -1;
while (choice != 0) {
System.out.println("Choose something: ");
System.out.println("-0 will exit the program" + "\n-Pressing 1 will open the database menu");
choice = in.nextInt();
switch(choice) {
case 0: choice = 0; break;
case 1: database(); break;
default: System.out.println("You have to choose either 0 or 1"); break;
}
}
}
public void database() {
System.out.println("Welcome to the database \nThese are the options:\n0 = Back to menu\n1: Riders");
int dbChoice = -1;
while (dbChoice != 0) {
System.out.println();
dbChoice = in.nextInt();
switch(dbChoice) {
case 0: dbChoice = 0; break;
case 1: cy.riders(); System.out.println("Press 0 for going back to the menu\nPress 1 for showing the riders");break;
default: System.out.println("Choose either 0 or 1"); break;
}
}
}
}
class Cyclist {
List<Cyclist> cyclists = new ArrayList<>();
private String name;
private int mountain;
private int timeTrial;
private int sprint;
private int age;
Cyclist c1 = null;
public void setName(String name) {
this.name = name;
}
public String getName() {
return name;
}
public void setMountain(int mountain) {
this.mountain = mountain;
}
public int getMountain() {
return mountain;
}
public void setTimeTrial(int timeTrial) {
this.timeTrial = timeTrial;
}
public int getTimeTrial() {
return timeTrial;
}
public void setSprint(int sprint) {
this.sprint = sprint;
}
public int getSprint() {
return sprint;
}
public void setAge(int age) {
this.age = age;
}
public int getAge() {
return age;
}
public void riders() {
abilities();
for (int i = 0; i < cyclists.size(); i++){
System.out.print(((Cyclist) cyclists).getName());
}
}
public void abilities() {
//Pardilla is created
c1 = new Cyclist();
c1.setName("Sergio Pardilla");
c1.setMountain(75);
c1.setTimeTrial(60);
c1.setSprint(60);
c1.setAge(30);
/*System.out.println(c1.getName() + "'s abilities:");
System.out.println("Mountain - " + c1.getMountain());
System.out.println("TimeTrial - " + c1.getTimeTrial());
System.out.println("Sprint - " + c1.getSprint());
System.out.println("Age - " +c1.getAge());
cyclists.add(c1); //adds Pardilla to cyclists arraylist*/
}
}

You have this for-loop:
for (int i = 0; i < cyclists.size(); i++) {
System.out.print(((Cyclist) cyclists).getName());
}
It is not going to work. You are casting the entire cyclists (an ArrayList) to one cyclist instance. You probably want to iterate over the contents of the ArrayList and get each Cyclist-object in the cyclists array. Try a foreach-loop:
for (Cyclist cyclist : cyclists) {
System.out.print(cyclist.getName());
}
or use a for loop with index based retrieval:
for (int i = 0; i < cyclists.size(); i++) {
cyclists.get(i).getName());
}

I think you want more something like:
public void riders() {
abilities();
for (int i = 0; i < cyclists.size(); i++){
System.out.print(cyclists.get(i).getName());
}
}
Another thing, is that I'm not sure you want List<Cyclist> cyclists = new ArrayList<>(); to be part of Cyclist class.

Two issues:
The part where you add your rider to the ArrayList is commented out.
The way you loop over your ArrayList is by no means correct. Try like this:
for (Cyclist cyclist : cyclists) {
System.out.println(cyclist.getName());
}

You should get Objects from List by calling it number: cyclists.get(i).getName())

Text User Interface, cannot get a method to work

I have an assignment to carry out using BlueJ where I am given a class called HW4CustomerList and I must create a Text-Based UI for it. The class I have to create is called CustomerTUI and contains a method called addCustomer which adds a new Customer object of mine to an ArrayList. This method in particular is what I am stuck with. The class specification says that I cannot take any parameters (i.e. a no-args method). In previous work we have used the BlueJ 'method box' to interact with objects and add them to ArrayLists, however I do not know if this can be used in this particular instance. Please find below my code so far for CustomerTUI and the code for the Customer class and HW4CustomerList class. Many thanks in advance.
CustomerTUI class:
import java.util.Scanner;
public class CustomerTUI
{
private HW4CustomerList customerList;
private Scanner myScanner;
public CustomerTUI()
{
customerList = new HW4CustomerList();
myScanner = new Scanner(System.in);
}
public void menu()
{
int command;
boolean running = true;
while(running)
{
displayMenu();
command = getCommand();
execute(command);
}
}
private void addCustomer()
{
customerList.addCustomer();
}
private void displayMenu()
{
System.out.println(" CustomerList program ");
System.out.println("=========================================");
System.out.println("|Add a customer to the list..........[1]|");
System.out.println("|Get number of customers.............[2]|");
System.out.println("|Remove a customer from the list.....[3]|");
System.out.println("|Show all customer details...........[4]|");
System.out.println("|Show a specific customers details...[5]|");
System.out.println("|Quit................................[6]|");
System.out.println("=========================================");
}
private void execute(int command)
{
if(command == 1)
{
addCustomer();
}
else if(command == 2)
{
getNumberOfCustomers();
}
else if(command == 3)
{
removeCustomer();
}
else if(command == 4)
{
showAllCustomers();
}
else if(command == 5)
{
showCustomer();
}
else if(command == 6)
{
quitCommand();
}
else
{
unknownCommand(command);
}
}
private int getCommand()
{
System.out.println("Enter the command of the function you wish to use: ");
int command = myScanner.nextInt();
return command;
}
private void getNumberOfCustomers()
{
if(customerList.getNumberOfCustomers() == 1)
{
System.out.println("We have " + customerList.getNumberOfCustomers() + " customer.");
}
else
{
System.out.println("We have " + customerList.getNumberOfCustomers() + " customers.");
}
}
private void quitCommand()
{
System.out.println("The program is now closing down...");
System.exit(0);
}
private void removeCustomer()
{
String accNo;
System.out.println("Enter the account number of the customer you wish to remove: ");
accNo = myScanner.next();
if (customerList.removeCustomer(accNo) == true)
{
System.out.println("Customer with account number " + accNo + " was successfully removed.");
}
else
{
System.out.println("Customer with account number " + accNo + " was NOT successfully removed.");
System.out.println("Please try again.");
}
}
private void showAllCustomers()
{
customerList.getAllCustomers();
}
private void showCustomer()
{
String accNo;
System.out.println("Enter the account number of the customer you wish to view: ");
accNo = myScanner.next();
if(customerList.getCustomer(accNo) == false)
{
System.out.println("Could not find customer with account number " + accNo + ".");
}
else
{
return;
}
}
private void unknownCommand(int command)
{
System.out.println("Command number " + command + " is not valid. Please try again.");
}
}
HW4CustomerList class:
import java.util.*;
public class HW4CustomerList
{
private ArrayList<Customer> customers;
public HW4CustomerList()
{
customers = new ArrayList<Customer>();
}
public void addCustomer(Customer customer)
{
customers.add(customer);
}
public int getNumberOfCustomers()
{
return customers.size();
}
public boolean getCustomer(String accountNumber)
{
for(Customer customer : customers)
{
if(accountNumber.equals(customer.getAccountNumber()))
{
customer.printCustomerDetails();
return true;
}
}
return false;
}
public void getAllCustomers()
{
for(Customer customer : customers)
{
customer.printCustomerDetails();
System.out.println("\n");
}
}
public boolean removeCustomer(String accountNumber)
{
int index = 0;
for (Customer customer: customers)
{
if (accountNumber.equals(customer.getAccountNumber()))
{
customers.remove(index);
return true;
}
index++;
}
return false;
}
}

I think all you need to do is create a new Customer object in your addCustomer() method. This would probably require getting additional details:
public void addCustomer()
{
Scanner scanner = new Scanner(System.in);
System.out.println("Enter customer name: ");
String name = scanner.nextLine();
//any additional details
Customer customer = new Customer(name, otherParams);
customers.add(customer);
}
Hope that helps!