如何在arrayList中搜索然后更改？

Question

So i'm making a supermarket program that allows to add products and sell them, so far i have this:

class Product
{
    String name;
    double price;
    int day;
    int month;
    int year;
    int stock;
    public Product(String name,double price,int day,int month,int year,int stock)
    {
        this.name=name;
        this.price=price;
        this.day=day;
        this.month=month;
        this.year=year;
        this.stock=stock;
    }
}

class SuperMarket{
    protected String name;
    protected int numMax;
    private List<Product> pr;
    
    public SuperMarket(String name,int numMax)
    {
        this.name=name;
        this.numMax=numMax;
        this.pr = new ArrayList<Product>();
        
    }
    public void addProduct() {
       //deleted to post here
    }
    
    public void sellProduct()//its here i need help
    {
        Scanner sc=new Scanner(System.in);
        System.out.println("What product do you want to sell?");
        String name=sc.nextLine();
                
    }
    
}

I´d like to know how to search in Product list by name and then change the stock(subtract-n) to sell n of that product.

Answer 1

You can use Stream API to find out the product by name. Filter the list by checking the name of product and get first match.

Optional<Product> product = productList.stream()
                                       .filter(e -> e.name.equals(inputedName))
                                       .findFirst();

Then can check is product found then update the stock

if(product.isPresent()){
   Product p = product.get();
   p.stock = p.stock - numberOfSoldProduct;
}

Suggestion to use getter/setter for fields.

Answer 2

In case if you are looking to get search using O(1), you can use map. however i don't see necessary of list though.

public SuperMarket(String storeName,int storeId){
    this.storeName = storeName;
    this.storeId = storeId;
    this.products = new ArrayList<Product>();
    this.productByName = new HashMap<String, Product>();
}

public void addProduct(Product product) {
    String productName = product.name;
    if(productByName.containsKey(productName)){
        Product existingProduct = productByName.get(productName);
        existingProduct.stock += product.stock;
        existingProduct.price = product.price;
    }else{
        productByName.put(productName, product);
        products.add(product);
    }
}

public void sellProduct(String productName, int count){
    if(!productByName.containsKey(productName)){
        System.out.println(productName + " is unavailable !!!");
        return;
    }
    Product existingProduct = productByName.get(productName);
    existingProduct.stock -= count;
    if(existingProduct.stock <= 0){
        productByName.remove(productName);
        products.remove(existingProduct);
    }
}

}