We Keep Coding

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.

Java program not saving object to HashMap

Either my save_product function in my Repository.java class doesn't save correctly into the map product_repository or, maybe it does save, but I'm not outputting it correctly in my find_product function in my Repository.java class. I think I'm using the correct function to search for the value in the map, .get
I experimented with product_repository.keySet().iterator().forEachRemaining(System.out::println); but that's the first time I ever used that... also please forgive how I insert the keyinto the map product_repository in the create_new_product function in the Controller.java class. I'm new to java ...
Main.java
package com.company;
public class Main {
public static void main(String[] args) {
// write your code here
Controller controller = new Controller();
controller.create_new_product();
controller.search_product();
}
}
Product.java
package com.company;
public class Product {
private String product_name;
private String product_brand;
private int product_cost;
private int product_count;
private boolean product_availability;
public Product() {
}
public Product(String product_name, String product_brand,
int product_cost, int product_count, boolean product_availability) {
this.product_name = product_name;
this.product_brand = product_brand;
this.product_cost = product_cost;
this.product_count = product_count;
this.product_availability = product_availability;
}
public String getProduct_name() {
return product_name;
}
public void setProduct_name(String product_name) {
this.product_name = product_name;
}
public String getProduct_brand() {
return product_brand;
}
public void setProduct_brand(String product_brand) {
this.product_brand = product_brand;
}
public int getProduct_cost() {
return product_cost;
}
public void setProduct_cost(int product_cost) {
this.product_cost = product_cost;
}
public int getProduct_count() {
return product_count;
}
public void setProduct_count(int product_count) {
this.product_count = product_count;
}
public boolean isProduct_availability() {
return product_availability;
}
public void setProduct_availability(boolean product_availability) {
this.product_availability = product_availability;
}
}
Controller.java
package com.company;
import java.util.Scanner;
public class Controller {
private static Long key;
public static void create_new_product(){
Repository repository = new Repository();
//Supplier supplier = new Supplier();
Product product = new Product();
Scanner scanner = new Scanner(System.in);
key = 0L;
System.out.println("*****************************************************************");
System.out.println("********************NEW PRODUCT CREATION PAGE********************");
System.out.println("*****************************************************************");
System.out.println("Enter product name: ");
String name = scanner.nextLine();
product.setProduct_name(name);
System.out.println("Enter product brand: ");
String brand = scanner.nextLine();
product.setProduct_brand(brand);
System.out.println("Enter product cost: ");
int cost = scanner.nextInt();
product.setProduct_cost(cost);
System.out.println("Enter amount of products in stock: ");
int amount = scanner.nextInt();
product.setProduct_count(amount);
key++;
repository.save_product(key, product);
}
public void search_product(){
Repository repository = new Repository();
Product product = new Product();
Scanner scanner = new Scanner(System.in);
System.out.println("*****************************************************************");
System.out.println("*************************FIND PRODUCT PAGE***********************");
System.out.println("*****************************************************************");
// TO DO: Choices or if/else blocks not executing properly
System.out.println("\nSearch by ID or name?\nPress '1' for ID. Press '2' for name: ");
String choice = scanner.next();
if (choice.equals("1")) {
System.out.println("Enter product id: ");
Long id = scanner.nextLong();
repository.find_product(id);
try{
if (product.getProduct_count() > 0){
System.out.println(product.getProduct_name() + " are in stock!");
}
} catch (Exception e) {
System.out.println(product.getProduct_name() + " are out of stock.");
}
}
else if (choice.equals("2")) {
System.out.println("Enter product name: ");
String name = scanner.next();
repository.find_product(name);
try{
if (product.getProduct_count() > 0){
System.out.println(product.getProduct_name() + " are in stock!");
}
} catch (Exception e) {
System.out.println(product.getProduct_name() + " are out of stock.");
}
}
else {
System.out.println("Error. We apologize for the inconvenience.");
}
}
}
Repository.java
package com.company;
import java.util.HashMap;
import java.util.Map;
public class Repository {
private Map<Long, Product> product_repository = new HashMap<Long, Product>();
// TO DO: Implement while loops so program doesn't exit at the first error
public void save_product(Long key, Product newProductMap){
try{
if (product_repository.containsValue(newProductMap)) {
System.out.println("This product is already in the system." +
"\nFor safety reasons, we cannot add the same product twice.");
}
else {
product_repository.put(key, newProductMap);
}
} catch (Exception e) {
System.out.println("System error. Consult the database administrator.");
}
}
public void find_product(Long key){
try {
if (product_repository.containsKey(key)) {
System.out.println(product_repository.get(key));
}
else {
System.out.println("No matches were found for product id: " + key);
}
} catch (Exception e) {
System.out.println("System error. Consult the database administrator.");
}
}
// Overload
public void find_product(String name) {
try {
if (product_repository.containsValue(name)) {
System.out.println(product_repository.get(name));
product_repository.keySet().iterator().forEachRemaining(System.out::println);
}
else {
System.out.println("No matches were found for product name: " + name);
}
} catch (Exception e) {
System.out.println("System error. Consult the database administrator.");
}
}
}

You have to make Repository repository a field of your Controller class. You are currently throwing the repositories away after your methods create_new_product and search_product have executed. Therefore you need to remove the first line of each of these methods.
Another problem is inside your find_product(String name) method where your call product_repository.get(name) but name is a String and the get method expects an ID, i.e. a Long so this call will always return null.

As it was pointed out before the repository has to be made global. However, the entire code is a bit messy. You are searching for a product id but the id is not shown to you. It is like searching for database records but the ids are autogenerated. Good luck with that. So I would suggest to allow this program to enter the id as well. It makes much more sense if you want to search for the id.
Otherwise, if you are interested in only the value, id can be taken out.
Below you can find the modified code that works for all the methods.
//main stays the same
public class Main {
public static void main(String[] args) {
// write your code here
Controller controller = new Controller();
controller.create_new_product();
controller.search_product();
}
}
//controller is a bit changed. Added global repository and improved the search.
import java.util.Collection;
import java.util.Scanner;
public class Controller {
private static Long key;
Repository repository = new Repository();
public void create_new_product() {
Product product = new Product();
Scanner scanner = new Scanner(System.in);
System.out.println("*****************************************************************");
System.out.println("********************NEW PRODUCT CREATION PAGE********************");
System.out.println("*****************************************************************");
System.out.println("Enter product id: ");
long id = Long.parseLong(scanner.nextLine());
product.setProductId(id);
System.out.println("Enter product name: ");
String name = scanner.nextLine();
product.setProduct_name(name);
System.out.println("Enter product brand: ");
String brand = scanner.nextLine();
product.setProduct_brand(brand);
System.out.println("Enter product cost: ");
int cost = scanner.nextInt();
product.setProduct_cost(cost);
System.out.println("Enter amount of products in stock: ");
int amount = scanner.nextInt();
product.setProduct_count(amount);
repository.save_product(id, product);
}
public void search_product() {
Scanner scanner = new Scanner(System.in);
System.out.println("*****************************************************************");
System.out.println("*************************FIND PRODUCT PAGE***********************");
System.out.println("*****************************************************************");
// TO DO: Choices or if/else blocks not executing properly
System.out.println("\nSearch by ID or name?\nPress '1' for ID. Press '2' for name: ");
String choice = scanner.next();
if (choice.equals("1")) {
System.out.println("Enter product id: ");
Long id = scanner.nextLong();
Product product = repository.find_product(id);
try {
if (product.getProduct_count() > 0) {
System.out.println(product.getProduct_name() + " are in stock!");
}
} catch (Exception e) {
System.out.println(product.getProduct_name() + " are out of stock.");
}
} else if (choice.equals("2")) {
System.out.println("Enter product name: ");
String name = scanner.next();
Collection<Product> products = repository.find_products(name);
if (products.size() > 0) {
for (Product product : products) {
System.out.println(product.getProduct_name() + " are in stock!");
}
} else {
System.out.println(" out of stock.");
}
} else {
System.out.println("Error. We apologize for the inconvenience.");
}
}
}
//Added a new field to the Repository so you can also search by key.
import java.util.*;
public class Repository {
private Map<Long, Product> product_repository = new HashMap<Long, Product>();
// TO DO: Implement while loops so program doesn't exit at the first error
public void save_product(Long key, Product newProductMap) {
try {
if (!product_repository.containsKey(key)) {
product_repository.put(key, newProductMap);
} else {
System.out.println("This product is already in the system." +
"\nFor safety reasons, we cannot add the same product twice.");
}
} catch (Exception e) {
System.out.println("System error. Consult the database administrator.");
}
}
public Product find_product(final Long key) {
try {
if (product_repository.containsKey(key)) {
System.out.println("Found product: " + product_repository.get(key).getProduct_name());
return product_repository.get(key);
} else {
System.out.println("No matches were found for product id: " + key);
}
} catch (Exception e) {
System.out.println("System error. Consult the database administrator.");
}
return null;
}
// Overload
public Collection<Product> find_products(final String name) {
Collection<Product> values = new ArrayList<>();
for (Map.Entry<Long, Product> productEntry : product_repository.entrySet()) {
if (productEntry.getValue().getProduct_name().equals(name)) {
System.out.println("matches were found for product name: " + name);
values.add(productEntry.getValue());
}
}
return values;
}
}

Reduce code duplication when reading different types of numbers from console

I have created three methods readLong, readInt and readDouble that basically does the same thing. Only difference is the method called by a scanner. How can I reduce duplicate code by turning them all to one method?
public long readLong(String description)
{
System.out.println(description);
long nrToReturn = 0;
boolean acceptedValue = false;
do {
System.out.println();
System.out.print("Choose one: ");
try
{
nrToReturn = consoleScanner.nextLong(); //Only line thats different except return value
acceptedValue = true;
}catch(Exception e)
{
acceptedValue = false;
consoleScanner.nextLine();
}
}while (!acceptedValue);
consoleScanner.nextLine();
return nrToReturn;
}

Here we go with one idea:
import java.util.Scanner;
public class ScannerTest {
private Scanner consoleScanner;
public ScannerTest() {
consoleScanner = new Scanner(System.in);
}
#SuppressWarnings("unchecked")
private <T extends Number> T readType(String description, Class<T> desiredType) {
System.out.println(description);
Number result = null;
while (result == null) {
System.out.println();
System.out.print("Choose one: ");
try {
if (Integer.class.equals(desiredType)) {
result = new Integer(consoleScanner.nextInt());
} else if (Long.class.equals(desiredType)) {
result = new Long(consoleScanner.nextLong());
}
} catch(Exception e) {
consoleScanner.nextLine();
}
}
consoleScanner.nextLine();
return (T) result;
}
public long readLong(String description) {
return this.readType(description, Long.class);
}
public int readInt(String description) {
return this.readType(description, Integer.class);
}
public static void main(String[] args) {
ScannerTest t = new ScannerTest();
t.readLong("Reading a long value...");
t.readInt("Reading an integer value...");
}
}
Update, following #Michu93 idea of a single transparent method:
import java.util.Scanner;
public class ScannerTest {
private Scanner consoleScanner;
public ScannerTest() {
consoleScanner = new Scanner(System.in);
}
#SuppressWarnings("unchecked")
public <T extends Number> T readNumber(String description) {
System.out.println(description);
Number result = null;
while (result == null) {
System.out.print("\nChoose one: ");
String textRead = consoleScanner.next();
try {
result = new Integer(textRead);
} catch(Exception e1) {
try {
result = new Long(textRead);
} catch (Exception e2) {
try {
result = new Double(textRead);
} catch (Exception e3) {
}
}
}
consoleScanner.nextLine();
}
return (T) result;
}
public static void main(String[] args) {
ScannerTest t = new ScannerTest();
for (int i = 0; i < 3; i++) {
Number input = t.readNumber(i + ": Reading int, long or double...");
System.out.println("Input class: " + input.getClass().getCanonicalName());
System.out.println("Input value: " + input);
}
}
}

Modify class to write exceptions to text file

I really just need a point in the right direction for this code. I do not understand how to accomplish what it is asking.
Modify the ProductMainApp class so it responds appropriately if the addProduct and deleteProduct mwthod in the ProductTextFile class returns a flase value.
Modify the ProductTextFile class so it writes exceptions to a tex file names errorLog.txt instead of printing them to the console. To do that, add a method named printToLogFile that accepts an IOException as an argument. This method should append two records to the log file: one that indicates the date and time the exception occured and one that contains information about the exception.
Modify the getProducts and saveProducts methods so they call the printToLogFile method when an error occurs.
Here is the PrintTextFile:
import java.util.*;
import java.io.*;
import java.nio.file.*;
public final class ProductTextFile implements ProductDAO
{
private ArrayList<Product> products = null;
private Path productsPath = null;
private File productsFile = null;
private final String FIELD_SEP = "\t";
public ProductTextFile()
{
productsPath = Paths.get("products.txt");
productsFile = productsPath.toFile();
products = this.getProducts();
}
public ArrayList<Product> getProducts()
{
// if the products file has already been read, don't read it again
if (products != null)
return products;
products = new ArrayList<>();
if (Files.exists(productsPath)) // prevent the FileNotFoundException
{
try
{
if (true)
{
// throw new IOException();
}
// open the input stream
BufferedReader in =
new BufferedReader(
new FileReader(productsFile));
// read all products stored in the file
// into the array list
String line = in.readLine();
while(line != null)
{
String[] columns = line.split(FIELD_SEP);
String code = columns[0];
String description = columns[1];
String price = columns[2];
Product p = new Product(
code, description, Double.parseDouble(price));
products.add(p);
line = in.readLine();
}
// close the input stream
in.close();
}
catch(IOException e)
{
//System.out.println(e);
return null;
}
}
return products;
}
public Product getProduct(String code)
{
for (Product p : products)
{
if (p.getCode().equals(code))
return p;
}
return null;
}
public boolean addProduct(Product p)
{
products.add(p);
return this.saveProducts();
}
public boolean deleteProduct(Product p)
{
products.remove(p);
return this.saveProducts();
}
public boolean updateProduct(Product newProduct)
{
// get the old product and remove it
Product oldProduct = this.getProduct(newProduct.getCode());
int i = products.indexOf(oldProduct);
products.remove(i);
// add the updated product
products.add(i, newProduct);
return this.saveProducts();
}
private boolean saveProducts()
{
try
{
// open the output stream
PrintWriter out = new PrintWriter(
new BufferedWriter(
new FileWriter(productsFile)));
// write all products in the array list
// to the file
for (Product p : products)
{
out.print(p.getCode() + FIELD_SEP);
out.print(p.getDescription() + FIELD_SEP);
out.println(p.getPrice());
}
// close the output stream
out.close();
}
catch(IOException e)
{
System.out.println(e);
return false;
}
return true;
}
}
Here is the ProductMainApp:
import java.util.Scanner;
import java.util.ArrayList;
public class ProductMaintApp implements ProductConstants
{
// declare two class variables
private static ProductDAO productDAO = null;
private static Scanner sc = null;
public static void main(String args[])
{
// display a welcome message
System.out.println("Welcome to the Product Maintenance application\n");
// set the class variables
productDAO = DAOFactory.getProductDAO();
sc = new Scanner(System.in);
// display the command menu
displayMenu();
// perform 1 or more actions
String action = "";
while (!action.equalsIgnoreCase("exit"))
{
// get the input from the user
action = Validator.getString(sc,
"Enter a command: ");
System.out.println();
if (action.equalsIgnoreCase("list"))
displayAllProducts();
else if (action.equalsIgnoreCase("add"))
{
addProduct();
}
else if (action.equalsIgnoreCase("del") || action.equalsIgnoreCase("delete"))
deleteProduct();
else if (action.equalsIgnoreCase("help") || action.equalsIgnoreCase("menu"))
displayMenu();
else if (action.equalsIgnoreCase("exit") || action.equalsIgnoreCase("quit"))
System.out.println("Bye.\n");
else
System.out.println("Error! Not a valid command.\n");
}
}
public static void displayMenu()
{
System.out.println("COMMAND MENU");
System.out.println("list - List all products");
System.out.println("add - Add a product");
System.out.println("del - Delete a product");
System.out.println("help - Show this menu");
System.out.println("exit - Exit this application\n");
}
public static void displayAllProducts()
{
System.out.println("PRODUCT LIST");
ArrayList<Product> products = productDAO.getProducts();
Product p = null;
StringBuilder sb = new StringBuilder();
if (productDAO.getProducts().equals(null))
{
System.out.println("Value Null");
System.exit(0);
}
for (int i = 0; i < products.size(); i++)
{
p = products.get(i);
sb.append(StringUtils.padWithSpaces(
p.getCode(), CODE_SIZE + 4));
sb.append(StringUtils.padWithSpaces(
p.getDescription(), DESCRIPTION_SIZE + 4));
sb.append(
p.getFormattedPrice());
sb.append("\n");
}
System.out.println(sb.toString());
}
public static void addProduct()
{
String code = Validator.getString(
sc, "Enter product code: ");
String description = Validator.getLine(
sc, "Enter product description: ");
double price = Validator.getDouble(
sc, "Enter price: ");
Product product = new Product();
product.setCode(code);
product.setDescription(description);
product.setPrice(price);
productDAO.addProduct(product);
System.out.println();
System.out.println(description
+ " has been added.\n");
}
public static void deleteProduct()
{
String code = Validator.getString(sc,
"Enter product code to delete: ");
Product p = productDAO.getProduct(code);
System.out.println();
if (p != null)
{
productDAO.deleteProduct(p);
System.out.println(p.getDescription()
+ " has been deleted.\n");
}
else
{
System.out.println("No product matches that code.\n");
}
}
}

You can use Exception.printStackTrace (stream) where stream is a outputstream to a file.
http://docs.oracle.com/javase/7/docs/api/java/lang/Throwable.html#printStackTrace(java.io.PrintStream)

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())