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ArrayList Collections error: which part of my code is wrong?

I would be required to write an array list of Mobile, do some operations such as add, remove, update and display. However, when it comes to sorting objects in arraylist, I am a little bit confused.
I am talking and referring to https://beginnersbook.com/2017/08/comparator-interface-in-java/
In drive class
//Create an arraylist of Mobile
ArrayList<Mobile> themobile = new ArrayList<>();
Scanner input = new Scanner(System.in);
System.out.println("Welcome to Mobile");
System.out.println("Please select a number in the following: ");
while (true) {
//A list of options
System.out.println("1. Diplay the next mobile.");
System.out.println("2. Display the previous mobile.");
System.out.println("3. Add a new mobile.");
System.out.println("4. Remove a new mobile");
System.out.println("5. Update a mobile.");
System.out.println("0. Exit");
//prompt user input
int choice = input.nextInt();
switch(choice) {
case 1:
//displayNext(themobile);
break;
case 2:
//displayPrevious(themobile);
break;
case 3:
addMobile(themobile);
break;
case 4:
removeMobile(themobile);
break;
case 5:
updateMobile(themobile);
break;
case 0:
System.out.println("Thank you for using a Mobile arraylist");
System.exit(0);
}
}
Collections.sort((themobile, new MobileByBrandName());
System.out.println("Sorted by brand name" + themobile);
Collections.sort(themobile, new MobileByMoNum());
System.out.println("Sorted by brand name" + themobile);
Collections.sort(themobile, new MobileByInS());
System.out.println("Sorted by brand name" + themobile);
}
In mobile class
public class Mobile implements Comparable<Mobile> {
private String brandName;
private int modelNumber;
private int internalMemoryS;
private int noOfAvailCameras;
public Mobile() {
}
public Mobile(String brandName, int modelNumber, int internalMemoryS, int noOfAvailCameras) {
this.brandName = brandName;
this.modelNumber = modelNumber;
this.internalMemoryS = internalMemoryS;
this.noOfAvailCameras = noOfAvailCameras;
}
public String getBrandName() {
return this.brandName;
}
public void setBrandName(String brandName) {
this.brandName = brandName;
}
public int getModelNumber() {
return this.modelNumber;
}
public void setModelNumber(int modelNumber) {
this.modelNumber = modelNumber;
}
public int getInternalMemoryS() {
return internalMemoryS;
}
public void setInternalMemoryS(int internalMemoryS) {
this.internalMemoryS = internalMemoryS;
}
public int getNoOfAvailCameras() {
return noOfAvailCameras;
}
public void setNoOfAvailCameras(int noOfAvailCameras) {
this.noOfAvailCameras = noOfAvailCameras;
}
public int compareTo(Mobile m) {
return this.brandName.compareTo(m.getBrandName());
}
public String toString() {
return "Brand name: " + brandName + "Model number: " + modelNumber + "Internal memory space: " + internalMemoryS + "No of available cameras: " + noOfAvailCameras;
}
}
Each method has its own class & import java.util.*;
public class MobileByMoNum implements Comparator<Mobile> {
public int compare(Mobile m1, Mobile m2) {
return m1.getModelNumber() - m2.getModelNumber();
}
}
public class MobileByBrandName implements Comparator<Mobile> {
public int compare(Mobile m1, Mobile m2) {
return m1.getBrandName().compareTo(m2.getBrandName());
}
}
public class MobileByInS implements Comparator<Mobile> {
public int compare(Mobile m1, Mobile m2) {
return m1.getInternalMemoryS() - m2.getInternalMemoryS();
}
}
Outcome:
TestMobile.java:48: error: unreachable statement
Collections.sort(themobile, new MobileByBrandName());
^
1 error
Any help and clarification is much appreciated. Thank you

As this code
while (true) {
never exits, the code below this loop is unreachable
Maybe System.exit(0); should maybe only be breaking the while loop.
Note break in a switch will not break the while loop

The code after while loop is never reached. You need to write some logic to break out of the while loop. One easy way to fix this is:
int choice = -1;
while (choice != 0) {
choice = input.nextInt();
switch (choice) {
//...other cases
case 0:
System.out.println("Thank you for using a Mobile arraylist");
}
}
Collections.sort(...);
System.out.println(...);

Put these lines inside while loop
Collections.sort((themobile, new MobileByBrandName());
System.out.println("Sorted by brand name" + themobile);
Collections.sort(themobile, new MobileByMoNum());
System.out.println("Sorted by brand name" + themobile);
Collections.sort(themobile, new MobileByInS());
System.out.println("Sorted by brand name" + themobile);
Also you can simplify the operation of comparison by using Comparator.comparing available from java 8 onwards. Like:
Comparator<Mobile> comparator = Comparator.comparing(new Function<Mobile,
#Override
public String apply(Mobile t) {
return t.getBrandName();
}
}).thenComparingInt(new ToIntFunction<Mobile>() {
#Override
public int applyAsInt(Mobile t) {
return t.getModelNumber();
}
}).thenComparingInt(new ToIntFunction<Mobile>() {
#Override
public int applyAsInt(Mobile t) {
return t.getInternalMemoryS();
}
});
Collections.sort(themobile, comparator);

How to add user input into an array

This is the parent class
public class Holding {
private String holdingId, title;
private int defaultLoanFee, maxLoanPeriod, calculateLateFee;
public Holding(String holdingId, String title){
this.holdingId = holdingId;
this.title = title;
}
public String getId(){
return this.holdingId;
}
public String getTitle(){
return this.title;
}
public int getDefaultLoanFee(){
return this.defaultLoanFee;
}
public int getMaxLoanPeriod(){
return this.maxLoanPeriod;
}
public void print(){
System.out.println("Title: " + getTitle());
System.out.println("ID: " + getId());
System.out.println("Loan Fee: " + getDefaultLoanFee());
System.out.println("Max Loan Period: " + getMaxLoanPeriod());
}
}
This is the child class:
public class Book extends Holding{
private String holdingId, title;
private final int defaultLoanFee = 10;
private final int maxLoanPeriod = 28;
public Book(String holdingId, String title){
super(holdingId, title);
}
public String getHoldingId() {
return holdingId;
}
public String getTitle(){
return title;
}
public int getDefautLoanFee(){
return defaultLoanFee;
}
public int getMaxLoanPeriod(){
return maxLoanPeriod;
}
public void print(){
System.out.println("Title: " + getTitle());
System.out.println("ID: " + getHoldingId());
System.out.println("Loan Fee: " + getDefaultLoanFee());
System.out.println("Max Loan Period: " + getMaxLoanPeriod());
}
}
This is the menu:
public class LibraryMenu {
static Holding[]holding = new Holding[15];
static int hold = 0;
static Scanner input = new Scanner(System.in);
public static void main(String[] args) {
Scanner keyboard = new Scanner(System.in);
int options = keyboard.nextInt();
do{
}
System.out.println();
System.out.println("Library Management System");
System.out.println("1. Add Holding");
System.out.println("2. Remove Holding");
switch(options){
case 1:
addHolding();
break;
default:
System.out.println("Please enter the following options");
}
}while(options == 13);
System.out.println("Thank you");
}
public static void addHolding(){
System.out.println("1. Book");
System.out.println("2. Video");
int input1 = input.nextInt();
switch(input1){
case 1:
addBook();
break;
case 2:
addVideo();
break;
default:
System.out.println("Please select the following options");
break;
}
}
public static void addBook(){
}
}
All i want is when a user wants to add a book, the user will type in the title and id for it and it will save into the array, and when it is done, it will go back to the menu. I cant seem to do it with my knowledge at the moment.
i tried to do this in the addBook() method
holding[hold] = new Book();
holding[hold].setBook();
the setBook method would be in the Book class, to complete the setBook, i have to make set methods for all the get method. But when i do this, the constructor is undefined.
public void setBook(){
System.out.println("Title: " + setTitle());
System.out.println("ID: " + setHoldingId());
System.out.println("Loan fee: " + setDefaultLoanFee());
System.out.println("Max Loan Period: " + setMaxLoanPeriod());
}
If there is anything wrong with my code, please feel free to say it to me :D
Thanks.
edit: After the user adds a book or video, when the user wants to print all the holdings, it will show the title, id, loan fee and max loan period. How do i do that?
edit2: Clean up a few parts that wasn't necessary with my question

I would suggest you to use "List of Object" concept in handling it.
1) You can define a List of Book object for example.
List<Book> bookList = new ArrayList<Book>();
2) Everytime when you hit AddBook() function, you can then do something like this.
//Create a temporary object of Book to get the user input data.
Book tempBook = new Book(holdingIDParam, titleParam);
//Add them to the list
bookList.Add(tempBook);
3) You can then use that list to your likings, whether to store them into a .txt based database or to use them throughout the program. Usage example:
bookList.get(theDesiredIndex).getBook() ...
I am not entirely sure of what you want but after paying focus on your bold text,this is what I can understand for your case. Feel free to correct me on your requirements if it doesn't meet.
Hope it helps :)

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())

Sorting Doubles using Comparator Program

I have developed a program that creates an array of Book Objects and sorts them based on user input. The sorting options are author-title-pages-price, and all work but the price sort. Please help me find where my application hangs... (I click the sort by price button and nothing shows up...)
My SchoolTextBook Class:
import java.util.Comparator;
public class SchoolTextBook {
private String author;
private String title;
private int pageCount;
private String ISBN;
private double price;
public String getAuthor() {
return author;
}
public void setAuthor(String author) {
this.author = author;
}
public String getTitle() {
return title;
}
public void setTitle(String title) {
this.title = title;
}
public int getPageCount() {
return pageCount;
}
public void setPageCount(int pageCount) {
this.pageCount = pageCount;
}
public String getISBN() {
return ISBN;
}
public void setISBN(String iSBN) {
ISBN = iSBN;
}
public double getPrice() {
return price;
}
public void setPrice(double price) {
this.price = price;
}
public static Comparator<SchoolTextBook> BookPriceComparator
= new Comparator<SchoolTextBook>() {
public int compare(SchoolTextBook book1, SchoolTextBook book2) {
double price1 = book1.getPrice();
double price2 = book2.getPrice();
//ascending order
return Double.compare(price1, price2);
}
};
}
And my SchoolTextBookSort Class:
import java.util.Arrays;
import java.util.*;
import javax.swing.*;
public class SchoolTextBookSort {
public static void main(String[] args) {
// TODO Auto-generated method stub
String[] choices = {"Author", "Title", "Page Count", "Price"};
SchoolTextBook[] theBooks = new SchoolTextBook[5];
theBooks[0] = new SchoolTextBook();
theBooks[1] = new SchoolTextBook();
theBooks[2] = new SchoolTextBook();
theBooks[3] = new SchoolTextBook();
theBooks[4] = new SchoolTextBook();
theBooks[0].setAuthor("Ernest Hemingway");
theBooks[1].setAuthor("Mark Twain");
theBooks[2].setAuthor("William Shakespeare");
theBooks[3].setAuthor("Stephen King");
theBooks[4].setAuthor("William Faulkner");
theBooks[0].setTitle("A Farewell to Arms");
theBooks[1].setTitle("The Adventures of Huckleberry Finn");
theBooks[2].setTitle("Hamlet");
theBooks[3].setTitle("Salem's Lot");
theBooks[4].setTitle("The Sound and the Fury");
theBooks[0].setPageCount(332);
theBooks[1].setPageCount(320);
theBooks[2].setPageCount(196);
theBooks[3].setPageCount(439);
theBooks[4].setPageCount(326);
theBooks[0].setISBN("0099910101");
theBooks[1].setISBN("0142437174");
theBooks[2].setISBN("0521618746");
theBooks[3].setISBN("0450031063");
theBooks[4].setISBN("0679732241");
theBooks[0].setPrice(5.99);
theBooks[1].setPrice(7.60);
theBooks[2].setPrice(9.41);
theBooks[3].setPrice(16.56);
theBooks[4].setPrice(9.60);
int response = JOptionPane.showOptionDialog(
null // Center in window.
, "Please select a method to sort the books." // Message
, "Sort Text Books" // Title in titlebar
, JOptionPane.YES_NO_OPTION // Option type
, JOptionPane.PLAIN_MESSAGE // messageType
, null // Icon (none)
, choices // Button text as above.
, null // Default button's label
);
//... Use a switch statement to check which button was clicked.
switch (response) {
case 0:
Arrays.sort(theBooks, SchoolTextBook.BookAuthorComparator);
break;
case 1:
Arrays.sort(theBooks, SchoolTextBook.BookTitleComparator);
break;
case 2:
Arrays.sort(theBooks, SchoolTextBook.BookPagesComparator);
break;
case 3:
Arrays.sort(theBooks, SchoolTextBook.BookPriceComparator);
case -1:
//... Both the quit button (3) and the close box(-1) handled here.
System.exit(0); // It would be better to exit loop, but...
default:
//... If we get here, something is wrong. Defensive programming.
JOptionPane.showMessageDialog(null, "Unexpected response " + response);
}
show(theBooks);
}
public static String show(SchoolTextBook[] theBooks) {
StringBuilder sb = new StringBuilder(64);
sb.append("<html><table><tr><td>Author</td><td>Title</td><td>ISBN</td><td>Pages</td><td>Price</td></tr>");
sb.append("<tr>");
sb.append("<td>").append(theBooks[0].getAuthor()).append("</td>");
sb.append("<td>").append(theBooks[0].getTitle()).append("</td>");
sb.append("<td>").append(theBooks[0].getISBN()).append("</td>");
sb.append("<td>").append(theBooks[0].getPageCount()).append("</td>");
sb.append("<td>").append("$" + theBooks[0].getPrice()).append("</td></tr>");
sb.append("<tr>");
sb.append("<td>").append(theBooks[1].getAuthor()).append("</td>");
sb.append("<td>").append(theBooks[1].getTitle()).append("</td>");
sb.append("<td>").append(theBooks[1].getISBN()).append("</td>");
sb.append("<td>").append(theBooks[1].getPageCount()).append("</td>");
sb.append("<td>").append("$" + theBooks[1].getPrice()).append("</td></tr>");
sb.append("<tr>");
sb.append("<td>").append(theBooks[2].getAuthor()).append("</td>");
sb.append("<td>").append(theBooks[2].getTitle()).append("</td>");
sb.append("<td>").append(theBooks[2].getISBN()).append("</td>");
sb.append("<td>").append(theBooks[2].getPageCount()).append("</td>");
sb.append("<td>").append("$" + theBooks[2].getPrice()).append("</td></tr>");
sb.append("<tr>");
sb.append("<td>").append(theBooks[3].getAuthor()).append("</td>");
sb.append("<td>").append(theBooks[3].getTitle()).append("</td>");
sb.append("<td>").append(theBooks[3].getISBN()).append("</td>");
sb.append("<td>").append(theBooks[3].getPageCount()).append("</td>");
sb.append("<td>").append("$" + theBooks[3].getPrice()).append("</td></tr>");
sb.append("<tr>");
sb.append("<td>").append(theBooks[4].getAuthor()).append("</td>");
sb.append("<td>").append(theBooks[4].getTitle()).append("</td>");
sb.append("<td>").append(theBooks[4].getISBN()).append("</td>");
sb.append("<td>").append(theBooks[4].getPageCount()).append("</td>");
sb.append("<td>").append("$" + theBooks[4].getPrice()).append("</td>");
sb.append("</tr></table></html>");
JOptionPane.showMessageDialog(null, sb);
return sb.toString();
}
}

You need to add break statements to some of your case conditions:
switch (response) {
case 0:
Arrays.sort(theBooks, SchoolTextBook.BookAuthorComparator);
break;
case 1:
Arrays.sort(theBooks, SchoolTextBook.BookTitleComparator);
break;
case 2:
Arrays.sort(theBooks, SchoolTextBook.BookPagesComparator);
break;
case 3:
Arrays.sort(theBooks, SchoolTextBook.BookPriceComparator);
break; // <---- Add this
case -1:
//... Both the quit button (3) and the close box(-1) handled here.
System.exit(0); // It would be better to exit loop, but...
break; // <---- Add this
default:
//... If we get here, something is wrong. Defensive programming.
JOptionPane.showMessageDialog(null, "Unexpected response " + response);
break; // <---- Add this
}
If you don't have break statements the program continues and evaluates all of the cases lower than it as if they were true. In other words, if case 3 was true it would do the sort, then it would move on to what happens in case -1 and act as if that was true, which causes the system to exit.

I have found that the problem resides in this code here:
case -1:
//... Both the quit button (3) and the close box(-1) handled here.
System.exit(0); // It would be better to exit loop, but...
default:
//... If we get here, something is wrong. Defensive programming.
JOptionPane.showMessageDialog(null, "Unexpected response " + response);
}
Not sure exactly what it is but this is what was hanging the application.

Adding userInput to EmployeeStore

I made an EmployeeStore to obviously store employee details such as name,id and email. I set up a menu and now whenever the user wants to add an employee i get stuck on what to do.
Here is my code:
MenuMethods:
//Imports
import java.util.Scanner;
//********************************************************************
public class MenuMethods
{
private static Scanner keyboard = new Scanner(System.in);
//Methods for the Company Application menu.
//Method for validating the choice.
public static int getMenuChoice(String menuString, int limit, String prompt, String errorMessage)
{
System.out.println(menuString);
int choice = inputAndValidateInt(1, limit, prompt, errorMessage);
return choice;
}
//********************************************************************
//This method is used in the getMenuChoice method.
public static int inputAndValidateInt(int min, int max, String prompt, String errorMessage)
{
int number;
boolean valid;
do {
System.out.print(prompt);
number = keyboard.nextInt();
valid = number <= max && number >= min;
if (!valid) {
System.out.println(errorMessage);
}
} while (!valid);
return number;
}
//********************************************************************
public void userInput()
{
}
//********************************************************************
}
Add Method:
//Add to the Hashmap : Employee.
public void add(Employee employee)
{
map.put(employee.getEmployeeName(), employee);
}
//********************************************************************
MainApp:
//Imports.
import java.util.Scanner;
//********************************************************************
public class MainApp
{
//The Scanner is declared here for use throughout the whole MainApp.
private static Scanner keyboard = new Scanner(System.in);
public static void main(String[] args)
{
new MainApp().start();
}
public void start()
{
//Create a Store named Store and add Employee's to the Store.
EmployeeStore Store = new EmployeeStore();
Store.add(new Employee ("James O' Carroll", 18,"hotmail.com"));
Store.add(new Employee ("Andy Carroll", 1171,"yahoo.com"));
Store.add(new Employee ("Luis Suarez", 7,"gmail.com"));
//********************************************************************
/*Test Code.
Store.searchByName("James O' Carroll");
Store.print();
Store.searchByEmail("gmail.com");
Employee andy = Store.searchByEmail("hotmail.com");
System.out.println(andy);
Employee employee = Store.searchByName("James O' Carroll");
if (employee != null)
{
employee.setEmployeeName("Joe");
employee.setEmployeeId(1);
employee.setEmployeeEmail("webmail.com");
Store.edit(employee);
Store.print();
}*/
//********************************************************************
int choice ;
System.out.println("Welcome to the Company Database.");
do
{
choice = MenuMethods.getMenuChoice(
"1.\tView All" +
"\n2.\tAdd" +
"\n3.\tDelete" +
"\n4.\tDelete All " +
"\n5.\tEdit" +
"\n6.\tSearch" +
"\n7.\tPrint"+
"\n8.\tExit", 8, "Please enter your choice:", "Error [1,8] Only");
//String temp = keyboard.nextLine(); This prevented entering the choice.
switch (choice)
{
case 1:
System.out.println("View All");
Store.print();
break;
case 2:
System.out.println("Add");
//Store.add();
break;
case 3:
System.out.println("Delete");
//Store.delete();
break;
case 4:
System.out.println("Delete All");
Store.clear();
break;
case 5:
System.out.println("Edit");
break;
case 6:
System.out.println("Search");
Store.clear();
break;
case 7:
System.out.println("Print");
Store.print();
break;
case 8:
System.out.println("Exit");
break;
}
} while (choice != 8);
}
}

I think you're missing the next steps, before adding the employee. Ask to the user about the Employee name and email, and only after that, add it to your Store.