NullPointerException

[Jexly_]

package Interfaces.InternetShop;
 
import java.io.IOException;
import java.util.Objects;
import java.util.Scanner;
import java.util.concurrent.TimeUnit;
 
public class HelloKitty {
 
    public static class colors {
        public static final String reset = "\u001B[0m";
        public static final String black = "\u001B[30m";
        public static final String red = "\u001B[31m";
        public static final String green = "\u001B[32m";
        public static final String yellow = "\u001B[33m";
        public static final String blue = "\u001B[34m";
        public static final String purple = "\u001B[35m";
        public static final String cyan = "\u001B[36m";
        public static final String white = "\u001B[37m";
    }
 
    public static class User {
        private final String login;
        private final String password;
 
        private User(String user, String password) {
            this.login = user;
            this.password = password;
        }
 
        public Basket purchased;
 
        private String getLogin() {
            return login;
        }
 
        private String getPassword() {
            return password;
        }
    }
 
    public static class ProductHelloKitty {
        String modelName;
        double price;
 
        public ProductHelloKitty(String modelName, double price) {
            this.modelName = modelName;
            this.price = price;
        }
    }
 
    public static class CategoryHelloKitty {
        String nameCategory;
        ProductHelloKitty[] productHelloKitties;
 
        public CategoryHelloKitty(String nameCategory, ProductHelloKitty[] productHelloKitties) {
            this.nameCategory = nameCategory;
            this.productHelloKitties = productHelloKitties;
        }
    }
 
    public static class Basket {
        ProductHelloKitty[] purchased;
 
        public Basket(ProductHelloKitty[] purchased) {
            this.purchased = purchased;
        }
    }
 
    public static void Buy() {
        Basket cards = new Basket(card);
        client.purchased = cards;
        System.out.println("Товарный чек");
        for(int i = 0; i < client.purchased.purchased.length; ++i) {
            if(client.purchased.purchased[i] == null) break;
            System.out.println((i+1) + ". " + client.purchased.purchased[i].modelName + " ------- "
                    + client.purchased.purchased[i].price);
        }
        double gc = getCash(client.purchased.purchased);
        System.out.print("Общая сумма покупок составляет -------" + gc);
 
    }
 
    public static double getCash(ProductHelloKitty[] p) {
        double cash = 0.0;
        for(int i = 0; i < p.length; ++i) {
            if(p[i] == null) break;
            cash+=p[i].price;
        }
        return cash;
    }
 
    public static void getBasket(ProductHelloKitty[] product) throws InterruptedException {
        for (int i = 0; i < product.length; i++) {
            if (product[i] == null) break;
            System.out.println((i+1) + ". " + product[i].modelName + " " + product[i].price + "UAH");
        }
        System.out.println("0. Назад");
        Scanner scanner = new Scanner(System.in);
        System.out.println("");
        int number = scanner.nextInt();
        System.out.println("");
        if (number == 0) getMenu();
    }
 
    public static void seeProduct(CategoryHelloKitty hk) throws InterruptedException {
        for (int i = 0; i < hk.productHelloKitties.length; i++) {
            System.out.println((i+1) + ". " + hk.productHelloKitties[i].modelName + " " + hk.productHelloKitties[i].price + "UAH");
        }
        System.out.println("0. Назад");
        Scanner scanner = new Scanner(System.in);
        System.out.println("");
        int number = scanner.nextInt();
        System.out.println("");
        if (number == 0) getMenu();
        else buyProduct(hk.productHelloKitties[number -1]);
    }
 
    public static void buyProduct(ProductHelloKitty product) throws InterruptedException {
        System.out.println("");
        System.out.println(colors.red + "Продукт " + product.modelName + " " + product.price + "UAH был добавлен в корзину" + colors.reset);
        System.out.println("");
        for (int i = 0; i < card.length; i++) {
            if (card[i] == null) {
                card[i] = product;
                break;
            } else {
                if (i+1 == card.length && card[i] == null) {
                    System.out.println("Ваша корзина заполнена");
                    break;
                }
            }
        }
        getCategory(all);
    }
 
    public static void getCategory(CategoryHelloKitty[] categoryHelloKitties) throws InterruptedException {
        for (int i = 0; i < categoryHelloKitties.length; i++) {
            System.out.println("#" + (i+1) + " " + categoryHelloKitties[i].nameCategory);
        }
        System.out.println("0. Назад");
        Scanner scanner = new Scanner(System.in);
        System.out.println("");
        int number = scanner.nextInt();
        System.out.println("");
        if (number == 0) getMenu();
        else seeProduct(all[number - 1]);
    }
 
    public static void Sleep() throws InterruptedException {
        TimeUnit.SECONDS.sleep(2);
    }
 
    public static void Redirect() {
        for (int i = 0; i < 200; i++) {
            System.out.println();
        }
    }
 
    private static void isAuth() throws InterruptedException, IOException {
        User user = new User("1", "2");
        Scanner scanner = new Scanner(System.in);
        System.out.println("Введите логин и пароль.\n");
 
        String userLogin = user.getLogin();
        String userPassword = user.getPassword();
 
        System.out.print("Логин: ");
        String userInputLogin = scanner.nextLine();
        System.out.print("Пароль: ");
        String userInputPassword = scanner.nextLine();
 
        if (Objects.equals(userLogin, userInputLogin) && Objects.equals(userPassword, userInputPassword)) {
            System.out.println("\nУспешно!");
            Sleep();
            System.out.println("\nПеренаправляем на сайт...");
            Sleep();
            Redirect();
        } else {
            System.out.println("Логин или пароль введены не верно.");
            System.exit(0);
        }
    }
 
    public static void getMenu() throws InterruptedException {
        System.out.println("Добро пожаловать в Hello Kitty/Melody магазин!\n");
        System.out.println("1.Каталог");
        System.out.println("2.Корзина");
        System.out.println("3.Оплатить");
        System.out.println("0.Выйти");
        Scanner scanner = new Scanner(System.in);
        System.out.println("");
        int number = scanner.nextInt();
        System.out.println("");
        switch (number) {
            case 1:
                getCategory(all);
                break;
            case 2:
                getBasket(card);
                break;
            case 3: {
                Buy();
                break;
            }
            case 0:
                Redirect();
                System.out.println("Будем рады если Вы зайдете к нам позже! <3");
                Sleep();
                System.exit(number);
        }
    }
 
    static ProductHelloKitty helloKitty1 = new ProductHelloKitty("Hello Kitty повар", 100);
    static ProductHelloKitty helloKitty2 = new ProductHelloKitty("Hello Kitty уборощица", 200);
 
 
    static ProductHelloKitty helloKitty3 = new ProductHelloKitty("Мелоди1", 300);
    static ProductHelloKitty helloKitty4 = new ProductHelloKitty("Мелоди2", 400);
 
    static ProductHelloKitty[] Type1 = {helloKitty1, helloKitty2};
    static ProductHelloKitty[] Type2 = {helloKitty3, helloKitty4};
 
    static CategoryHelloKitty type1 = new CategoryHelloKitty("Hello Kitty ассортимент", Type1);
    static CategoryHelloKitty type2 = new CategoryHelloKitty("Melody ассортимент", Type2);
 
    static CategoryHelloKitty[] all = {type1, type2};
    static ProductHelloKitty[] card;
 
    static User client;
 
    public static void main(String[] args) throws InterruptedException, IOException {
        card = new ProductHelloKitty[20];
        isAuth();
        getMenu();
    }
}

Compile
write 1
then write 2
WAIT 4 SECONDS
then write 3

Why when I write 3, my code not working and show me error NullPointerException.

[Norm]

how me error NullPointerException.

What statement does that happen on? What variable has the null value? If you can not tell, Add a print statement just before the statement that has the NPE to print out the values of all the variables used in the statement that has the NPE.
Backtrack in the code to see Why that variable does not have a valid value?

[Jexly_]

Could you explain to me in more detail how I can fix the error? I do not understand

--- Update ---

I do

System.out.println(client.purchased);

And receive again error.

--- Update ---

So this variable is null, right? I need do client.purchased = 0; ?

[Norm]

What is the value in client when that statement is executed?
If it is null, backtrack in the code to see why client does not have a valid value.

[Jexly_]

But also I can't do this client.purchased = 0; So I don't know how to fix

--- Update ---

I already re-read the code, but I still can't figure out where my mistake is.

--- Update ---

public static void Buy() {
        Basket cards = new Basket(card);
        client.purchased = cards;
        System.out.println("Товарный чек");
        for(int i = 0; i < client.purchased.purchased.length; ++i) {
            if(client.purchased.purchased[i] == null) break;
            System.out.println((i+1) + ". " + client.purchased.purchased[i].modelName + " ------- "
                    + client.purchased.purchased[i].price);
        }
        double gc = getCash(client.purchased.purchased);
        System.out.print("Общая сумма покупок составляет -------" + gc);
 
    }

I think problem is here. client.purchased = cards;

[Norm]

Where is the variable client assigned a value?
client needs a valid value to keep from getting a NPE when it is used to reference an instance of a class.

[Jexly_]

Basket cards = new Basket(card);
client.purchased = cards;

I think here

--- Update ---

But I can't understand WHERE i need define

--- Update ---

I'm asked for help. Just tell me where I need fix. I'll understand later why I had to change the values there. Now we are playing with you the game "guess where it is wrong."

Can you help me?

[Norm]

What value needs to be in the client variable?
Where and when should that value be assigned to the client variable.

I do not know what the code is supposed to be doing. There are no comments in English describing the purpose of the program.
I can't suggest changes to the code without knowing what the code is supposed to do.

[patricajohnson51]

The `NullPointerException` you're encountering when you input '3' is likely due to the `client` object being null. In your code, `client` is declared but never initialized. Hence, when you call the `Buy()` method which references `client`, it throws a `NullPointerException`.

To fix this issue, you need to initialize the `client` object before calling `Buy()`. You can do this by instantiating a new `User` object and assigning it to `client` in your `isAuth()` method.

Here's how you can modify your `isAuth()` method to initialize the `client` object:

```java
private static void isAuth() throws InterruptedException, IOException {
User user = new User("1", "2");
Scanner scanner = new Scanner(System.in);
System.out.println("Введите логин и пароль.\n");

String userLogin = user.getLogin();
String userPassword = user.getPassword();

System.out.print("Логин: ");
String userInputLogin = scanner.nextLine();
System.out.print("Пароль: ");
String userInputPassword = scanner.nextLine();

if (Objects.equals(userLogin, userInputLogin) && Objects.equals(userPassword, userInputPassword)) {
System.out.println("\nУспешно!");
client = user; // Initialize the client object
Sleep();
System.out.println("\nПеренаправляем на сайт...");
Sleep();
Redirect();
} else {
System.out.println("Логин или пароль введены не верно.");
System.exit(0);
}
}
```

By initializing the client object in the isAuth() method, you ensure that it is not null when you call the Buy() method later in your code. This should resolve the NullPointerException issue. If you still encounter any challenges with your Java assignment, seeking assistance from resources like online assignment help platform like ProgrammingHomeworkHelp.com, online programming communities or educational platforms can provide valuable insights and support.