Develop Reference

JAVA Store Program isn't outputting the correct numbers

I was creating a Java program for my OOP class. The program is supposed to be the start of a store interface and we are going to build off it during the rest of the semester. Whenever I was to add a new product and try to access how much of it is in stock my program says the "Id DNE -1" which is only supposed to print when an id is called and it doesn't exist. I'm not too sure why it's not recognizing the product I just put in. Below are all my classes that are used. I think the error has to be somewhere in my inventory class but I'm not too sure. Any tips or tricks for OOP would greatly be appreciated as well. Cheers
public class main
{
public static void main(String[] args)
{
StoreManager r3 = new StoreManager();
Inventory r4 = new Inventory();
r4.addNewProduct(1,"apple",1.50,50);
System.out.println(r3.qCheck(1));
}
}
public class StoreManager
{
private Inventory store1 = new Inventory();
private Product store2 = new Product();
static Inventory r4 = new Inventory();
public StoreManager(){}
public int qCheck(int id)
{
if (store1.getStock(id) < 0)
{
System.out.println("Id DNE");
return -1;
} else
{
return store1.getStock(id);
}
}
public double dqcheck(int id, int desiredQuantity) {
if (store1.getStock(id) >= desiredQuantity) {
store1.removeStock(id, desiredQuantity);
double cost = store2.getPrice() * desiredQuantity;
return cost;
}
else {
System.out.println("id DNE");
}
return -1;
}
}
import java.util.HashMap;
import java.util.Iterator;
import java.util.Map;
import java.util.Set;
public class Inventory
{
//Var Declarations
private int quantity;
// FIXME: 2021-02-07 idk if im usin type right
private Product type;
//Hashmap for the data structure in this class using the Product is gonna be a key
// the value is the Integer for the quantity
private Map<Product,Integer> invt = new HashMap<>();
//blank constructor
public Inventory()
{
}
// FIXME: 2021-02-05 Getter and setter methods not really in use
public int getQuantity(){return quantity;}
public Product getType(){return type;}
/*
Used to initialize a new product and its stock into our Hashmap
the Quantity is the Value of our hashmap while we are using the
Product as a whole to be the key
no return type
*/
public void addNewProduct(int id,String name, double price, int quantity)
{
Product product = new Product(name, id, price);
invt.put(product,quantity);
}
/*
Used to get the get for a given id
compares the Id to one of the ids in the Key values to find the product
returns an int for the amount in stock or a -1 as an error if the id doesn't exist
*/
public int getStock(int id)
{
Set<Product> set = invt.keySet(); // Conversion of keys into sets
Iterator<Product> it = set.iterator(); // the only way i could get the code to interate throughout the keys
while (it.hasNext())//Only way i could go through the code
{
type = it.next();// FIXME: 2021-02-07 Idk if type is being used right here but i needed a buffer variable for it to work
Product a = it.next();
if (a.getId() == id)
{
return invt.get(type);//type is an object of Product here so we can use it as a key
}
}
return -1;//representation of error ID Dne
}
/*
Used to add a given Stock for a given Id
void doesnt return anything
assuming inpputed id exists if Dne doesnt do anythin or return an error
*/
public void addStock(int id, int amountToAdd)
{
//Possibly make this hashmap id check into another private method and call
Set<Product> set = invt.keySet();
Iterator<Product> it = set.iterator();
while (it.hasNext())
{
type = it.next();
if (type.getId() == id)
{
invt.put(type, invt.get(type)+amountToAdd);
return;//exit the function after the addtion is done
}
}
}
/*
Used to remove a given amount of product from stock in reference to a given Id
void doesnt return anythin
assuming id exits otherwise it does nothin
*/
public void removeStock(int id, int amountToRemove)
{
Set<Product> set = invt.keySet();
Iterator<Product> it = set.iterator();
while (it.hasNext())
{
type = it.next();
if (type.getId() == id && invt.get(type) - amountToRemove >= 0)//checks if the id exits and if there whould be enough stock to remove
{
invt.put(type, invt.get(type)-amountToRemove);
return;
}
}
}
/*
Prints all product information in reference to the id
*/
public void getInfo(int id)
{
Set<Product> set = invt.keySet();
Iterator<Product> it = set.iterator();
while (it.hasNext())
{
type = it.next();
if (type.getId() == id)
{
System.out.println("Name: "+type.getName());
System.out.println("Id: "+type.getId());
System.out.println("Price: "+type.getPrice());
System.out.println("Quantity: "+ invt.get(type)); // FIXME: 2021-02-07 Idk if Quanitity and Id are needed here
}
}
}
}
public class Product
{
private String name;
private int Id;
private double price;
public Product(String Name, int Id,double Price)
{
this.name = Name;
this.Id = Id;
this.price = Price;
}
public Product()
{
}
//Getter Methods
public String getName() {return name;}
public int getId() {return Id;}
public double getPrice() {return price;}
}

public class main
{
public static void main(String[] args)
{
StoreManager r3 = new StoreManager();
r3.store1.addNewProduct(1,"apple",1.50,50);
System.out.println(r3.qCheck(1));
}
}
Use the Inventory object that belongs to StoreManager, that's the only one it can access.

How can i change a value in an generic arraylist?

It's a code about a 'shopping cart' that can hold items of a class called 'item'. I had to complete the class 'item' and write another class 'discount' that can reduces the price of an item.
import java.util.ArrayList;
public class Shoppingcart extends Item {
// all shopping carts:
private ArrayList<Shoppingcart> allshoppingcart = new ArrayList<Shoppingcart>();
//Items in the shopping cart:
private ArrayList<Item> content = new ArrayList<Item>();
// Counter for shopping carts
private static int number;
/**
* Constructor
*/
public Shoppingcart() {
allshoppingcart .add(this);
this.number = number ;
this.number++;
}
/**
* load something in Shoppingcart
*/
public void load(Item i) {
this.content.add(i);
}
/**
* Sum of all items loaded in the shoppingcart
*
* #return sum of the content in the shopping cart
*/
public double sumShoppingCart() {
double sum = 0.0;
for (Item i : content) {
sum = sum + item.getPrice();
}
return sum;
}
}
The class 'item' so I can store two different types in the arraylist.
public class Item {
// normal price of item
protected double price;
// Name of product
protected String name;
/**
* setter for price and name
*/
public void setPB(String name, double price) {
this.name = name;
this.price = price;
}
/**
* getter for price
*/
public double getPrice() {
return this.price;
}
/**
* getter for the name
*/
public String getName() {
return this.name;
}
}
The class 'discount' to reduce an item for an example like a sale (special-offer).
public class Discount extends Item
{
// instance variables - replace the example below with your own
public Discount()
{
// initialise instance variables
}
public void makeSale(int percent){
percent =(100-percent)/100;
price = w.getPrice()*percent;
}
}
A test class
import java.util.ArrayList;
public class Test {
public static void main(String[] args) {
ArrayList<Item> content = new ArrayList<>();
Item item = new Item();
Item item1 = new Item();
Item item2 = new Item();
item.setPB("Steak", 100.00);
item1.setPB("Water", 200.00);
item2.setPB("Groceries", 300.00);
content.add(item);
content.add(item1);
content.add(item2);
System.out.println("The item has the value : " + item.getPrice() + " and the name: " + item.getName());
System.out.println("There are : " + content.size() + " Item(s) in the shopping cart.");
}
}
How do I access an item and reduce it for a sale?
Thank you

This is a typical OOP exercise. You want to access two different types in a single collection. To do so they both need to have the same interface or parent.
If you use an Abstract base class you can use the following example.
First lets make an abstract Item class:
abstract class Item {
protected double price;
protected String name;
public Item(double price, String name) {
this.price = price;
this.name = name;
}
public double getPrice() {
return this.price;
}
public void setName(String name) {
this.name = name;
}
public String getName() {
return this.name;
}
public void setPrice(double price) {
this.price = price;
}
abstract void discount(double amount);
}
and two classes that extend from this base class:
class Food extends Item {
public Food(double price, String name) {
super(price, name);
}
#Override
void discount(double amount) {
this.price -= amount;
}
}
class Bevarage extends Item {
public Bevarage(double price, String name) {
super(price, name);
}
#Override
void discount(double amount) {
this.price -= amount;
}
}
Now lets make a class discount that has a List items that can discount both items.
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
public class Discount {
public void printAllContent(List<Item> items) {
items.forEach(item -> System.out.printf("name = %s, price = %.00f \n", item.getName(), item.getPrice()));
}
public static void main(String[] args) {
Discount card = new Discount();
List<Item> items = Arrays.asList(
new Food(3.0, "burgers"), new Food(9.0, "tomato"), new Food(8.0, "fries"),
new Bevarage(9.0, "cola"), new Bevarage(12.0, "water"), new Food(2.0, "beer")
);
card.printAllContent(items);
for (Item item : items) {
item.discount(1.0);
}
card.printAllContent(items);
// if you want to do different discounts for different items
for(Item item: items) {
if (item instanceof Bevarage) {
item.discount(2.0);
} else {
item.discount(1.0);
}
}
card.printAllContent(items);
}
}

java.util.List has these functions get(index) and set(index, object), which you could use:
//1. get your item
int index = 0;
Item item=content.get(index);
//2. create your discount
Discount discount=new Discount();
// Fill/process your discount object with the appropriate data
//3. replace the item with the discount in the list
content.set(index,discount);

Adding to an object ArrayList from another Class

I have a Class named Item.
public class Item {
private int code;
private String name;
private double price;
private int quantity;
public Item(int code, String name, double price, int quantity) {
setCode(code);
setName(name);
setPrice(price);
setQuantity(quantity);
}
//Item getters and setters
And I have a Class named Stock that creates an ArrayList of Items.
public class Stock {
private ArrayList<Item> stock;
public Stock() {
stock = new ArrayList<Item>();
}
public ArrayList<Item> getStock() {
return stock;
}
I also have a Class named ItemRegister that adds an Item to the Stock.
public class ItemRegister extends Stock {
public void registerItem(String name, double price) {
getStock().add(new Item(setItemCode(), name, price, 0));
}
private int setItemCode() {
return getStock().size() + 1;
}
I'm using unit tests to see if I did add an Item to the Stock.
public class ItemRegisterTest {
#Test
public void testIfHasRegisteredItemInStock() {
Stock s = new Stock();
assertTrue(s.getStock().size() == 0);
ItemRegister i = new ItemRegister();
i.registerItem("Oleo", 20.0);
assertTrue(s.getStock().size() == 1);
}
}
When I run these tests it is returning an error.
On the second assertTrue, if I test with the object i it'll return true but what I want is to add to Stock and not ItemRegister because if later on I wanna consult Stock I'll call Stock and not ItemRegister.

From the comments, what you can do is maybe changing the parent-child relationship and having the ItemRegister holding an instance of a Stock object. So, you can modify the ItemRegister class like this:
public class ItemRegister {
Stock s;
public ItemRegister(Stock s) {
this.s = s;
}
public void registerItem(String name, double price) {
s.getStock().add(new Item(setItemCode(), name, price, 0));
}
private int setItemCode() {
return s.getStock().size() + 1;
}
}
Then, the test code you originally wrote will be true with a slight modification ItemRegister i = new ItemRegister(s);, and you can work on one instance of Stock object.

I want is to add to Stock and not ItemRegister because if later on I wanna consult Stock I'll call Stock and not ItemRegister.
Then you need to wrap Stock into ItemRegister.
public class ItemRegister {
Stock stock;
public ItemRegister(Stock stock) {
this.stock = stock;
}
public void registerItem(String name, double price) {
stock.getStock().add(new Item(setItemCode(), name, price, 0));
}
private int setItemCode() {
return stock.getStock().size() + 1;
}
}
Use it in your unit tests like this:
public class ItemRegisterTest {
#Test
public void testIfHasRegisteredItemInStock() {
Stock s = new Stock();
assertTrue(s.getStock().size() == 0);
ItemRegister i = new ItemRegister(s);
i.registerItem("Oleo", 20.0);
assertTrue(s.getStock().size() == 1);
}
}

How to create a better object

Related to my previous thread, i want to print an output like this:
bookId = "1234" (String)
bookName = "Machine Learning" (String)
price = $20 (int)
ratings = (array of object)
rater = a, score = 5
rater = b, score = 3
But this time, i tried to use an OOP manner.
So first, i made a POJO class called ProductView, the class will be look like this:
public class ProductView {
// field
private String bookId;
private String bookName;
private int price;
private List<Ratings> ratings;
// a constructor i tried to make
public ProductView(String bookId, String bookName, int price, List<Ratings> ratings) {
this.bookId = bookId;
this.bookName = bookName;
this.price = price;
this.ratings = ratings;
}
public String getBookId() {
return bookId;
}
public void setBookId(String bookId) {
this.itemId = itemId;
}
public String getBookName() {
return bookName;
}
public void setBookName(String bookName) {
this.bookName = bookName;
}
public int getPrice() {
return price;
}
public void setPrice(int price) {
this.price = price;
}
public Ratings getRatings() {
return ratings;
}
public void setRatings(Ratings ratings) {
this.ratings = ratings;
}
}
After that, i made a class called Ratings with the following field:
public class Ratings {
private String rater;
private int score;
public Ratings(String rater, int score) {
this.rater = rater;
this.score = score;
}
}
And finally, i made a Main Class called Main:
public class Main {
public static void main(String[] args) {
}
}
In the Main Class, i want to create an instance of the ProductView class and give it some value.
But i don't know how to do it with a list object param in my constructor.
Anyone can give me some insight?

first:
List is an interface, you should pass an implementation of list such as ArrayList or similar
second:
you have a compilation error in ProductView -> SetBookId, in this.itemId you don't have itemId as member or constructor parameter
furthermore, in get/set rating you need to pass and return list of Ratings.
nameing:
Ratings is actually just a Rating, you can make a new class of List or just use the Rating as is but change the name
now for your Question:
you can initialize first the list with objects and then send it to the constructor
such as:
List<Ratings> ratings = new ArrayList<>();
ratings.add(new Ratings("rater",5));
ratings.add(new Ratings("rater2",6));
ProductView productView = new ProductView("bookId","bookName",1,ratings);
Or, just initialize the ArrayList in the Constructor, the first way is preferable:
ProductView productView1 = new ProductView("bookId","bookName",1,
new ArrayList<Ratings>(Arrays.asList(new Ratings("rater",5), new Ratings("rater2",6))
));
hopefully, this answers your question
same as DodgyCodeException mentioned in the comments.

How to get product details based on product category, in java HashMap?

There is HashMap. I added all the product details in hashmap. I want to display the product details based on category. It means all same category products should be display. I am trying to create method for that. The method name is
public List<Product> getProductsBasedOnCategory(String category)
{
}
Please find below code.
Product.java
public class Product {
private long pid;
private String pname;
private String category;
private float price;
private long stock;
private String remarks;
public Product()
{
}
public Product(long pid,String pname,String category,float price,long stock,String remarks){
this.pid=pid;
this.pname=pname;
this.category=category;
this.price=price;
this.stock=stock;
this.remarks=remarks;
}
public long getPid() {
return pid;
}
public void setPid(long pid) {
this.pid = pid;
}
public String getPname() {
return pname;
}
public void setPname(String pname) {
this.pname = pname;
}
public String getCategory() {
return category;
}
public void setCategory(String category) {
this.category = category;
}
public float getPrice() {
return price;
}
public void setPrice(float price) {
this.price = price;
}
public long getStock() {
return stock;
}
public void setStock(long stock) {
this.stock = stock;
}
public String getRemarks() {
return remarks;
}
public void setRemarks(String remarks) {
this.remarks = remarks;
}
}
DatabaseClass.java
public class DatabaseClass {
private static Map<Long, Product> products=new HashMap<>();
public static Map<Long, Product> getProduct()
{
return products;
}
}
ProductDao.java
private Map<Long, Product> products=DatabaseClass.getProduct();
public ProductDaoImpl()
{
products.put(1L, new Product(1L,"TV","Entertinement",10000F,250L,"This is best TV!"));
products.put(2L, new Product(2L,"Computer","Technology",20000F,350L,"My Computer name Hp and SONY ViVo!"));
products.put(3L, new Product(3L,"DeskTopComputer","Technology",15000F,150L,"My Desktop Computer name Accer and SONY ViVo!"));
}
//Get All products
public List<Product> getAllProducts() {
return new ArrayList<Product>(products.values());
}
//Get product by product id
public Product getProduct(long pid) {
return products.get(pid);
}
//To Add the products
public Product addProduct(Product product) {
product.setPid(products.size()+1);
products.put(product.getPid(), product);
return product;
}
//Update the product
public Product updateProduct(Product product) {
if(product.getPid()<=0)
{
return null;
}
products.put(product.getPid(), product);
return product;
}
// Delete the product
public Product deleteProduct(long pid) {
return products.remove(pid);
}
//Get the product by category
public List<Product> getProductByCategory(String category) {
if(products.size()<=0)
{
return null;
}
else if(category.equals(products.get(Product))
{
}
I am trying a lot how to write code to get the value of model class in HashMap.
And how to write code for above getProductByCategory(String category).

You can iterate over the set of values in the map, and filter to return the list of matching products:
public List<Product> getProductByCategory(String category) {
if(products.size() == 0){
return new ArrayList<>();
}
return this.products.values().stream()
.filter(product -> product.getCategory().equals(category))
.collect(Collectors.toList());
}
You can also use a for-loop for that:
public List<Product> getProductByCategory(String category) {
List<Product> ret = new ArrayList<>();
if(products.size() == 0){
return ret;
}
for(Product p: this.products.values()) {
if(p.getCategory().equals(category))
ret.add(p);
}
return ret;
}
Please note that I return an empty ArrayList if the product map is empty. This is better practice for collection return types (instead of returning null)

One way is to iterate over the Hashmap as follows :
public List<Product> getProductsBasedOnCategory(String category)
{
List<Product> list = new ArrayList<Product>();
if (products.size()<=0) {
return list;
}
products.entrySet().stream().forEach((entry) -> {
if (((Product) entry.getValue()).getCategory().equals(category)) {
list.add(entry.getValue())
}
});
return list;
}

You have at least 2 options such as.
Have a specific map for each field you want to search by. This is
going to be faster if you have a lot of objects since searching in a
map takes O(1) while iterating through the entire collection takes
O(N). Big O Cheat Sheet
Declare the maps
private Map<Long, Product> productsByID = new HashMap();
private Map<String, Product> productsByCategory = new HashMap();
Initialize the maps
public ProductDaoImpl()
{
// Create the objects
Product p1 = new Product(1L,"TV","Entertinement",10000F,250L,"This is best TV!");
Product p2 = new Product(2L,"Computer","Technology",20000F,350L,"My Computer name Hp and SONY ViVo!");
Product p3 = new Product(3L,"DeskTopComputer","Technology",15000F,150L,"My Desktop Computer name Accer and SONY ViVo!");
//Assign the objects into the map by ids
productsByID.put(1L, p1);
productsByID.put(2L, p2);
productsByID.put(3L, p3);
//Assign the objects into the map by category
productsByCategory.put(p1.getCategory(), p1);
productsByCategory.put(p2.getCategory(), p2);
productsByCategory.put(p3.getCategory(), p3);
}
Use the same map you have and pretty
much iterate through all the values as the other answers explained.
Last,I don't know if this is just a exercise code and you have few values in which case the performance it doesn't matter that much or this is the beginning of your production code in which case you want to expect a lot of values.
If the latest is true, probably you want to model this into a DB (sql or not sql) and query by the specific field you want/need.