Long arrays calculation java

Question

I am a novice programmer and having issues understanding arrays. I have two String arrays:

String[] itemList = {"item1", "item2", "item3",....."item10"}

String[] country = {"US", "UK", "France",....."Germany"}

As you probably understood, the idea is, I should be able to choose an item from itemList, select a countryand the program should show me how much that specific item costs in that country. Now, I can use if statementand say something:

ìf(itemList[i] == "item1" && country[i] == "US"){ //check the price for item1 in the US...}.

This works alright if we have smaller amount of items, but what if the array of items is too big, like hundreds of thousands? The code will be extremely huge if I go with if statement for every item. Can you guys suggest a better solution? Thank you in advance!

Answer 1

Make an Item object (In a separate class... Item.class)

import java.util.Map;
import java.util.HashMap;

public class Item {
    private final String name;
    // <CountryName, Price>
    private Map<String, Double> countryPrices;

    public Item(String name) {
        this.name = name;
        this.countryPrices = new HashMap<>();
    }

    public String getName() {
        return this.name;
    }
    public void setPrice(String countryName, double price) {
        this.countryPrices.put(countryName, price);
    }
    public double getPrice(String countryName) {
        return this.countryPrices.get(countryName);
    }
}

If this were a serious application, use BigDecimal for more precise prices.

Also, you may want to create a Country enum so you don't have to always make sure you spell them correctly and use correct upper-case / lower-case letters.

To use this, create a list of items:

List<Item> items = new ArrayList<>();

Then to add a new item:

Item someItem = new Item();
someItem.setPrice("USA", 2.99);

Then, to get an item's price depending on a given country name:

// get from user input
String countryName =...
String itemName =...

// loop  through the items list we created
for (Item item : items) {
    if (item.getName().equalsIgnoreCase(itemName)) {
        // we found the item we are looking for! get the price
        double price = item.getPrice(countryName);
        // do what you want with this...
        System.out.println(itemName + "'s price in " + countryName + " is " + price + ".");
        // We are done looking - we found the item and got it's price. End the loop
        break;
    }
}

Sidenote: As @JacobG. said, don't compare strings with ==

Answer 2

I got your problem here.

A few things I would like to mention is

1. String comparisons doesn’t work with ==, double check how and why.
2. Also you need to work on your logic, if else won’t help if combinations goes beyond something that you can handle. So, I am assuming based on Country and Currency you need to show price of a particular item. I’ll highlight some points for you to think over: Countries are finite while number of Items can change. Also you have to maintain something for Price conversion from Base currency to Countries Currency. Think along those lines and you will be fine.
   3. As you are a newbie to programming, I will suggest not to worry about Length for now. For most cases Arrays would be just fine, and for complex purposes of large lists we use various approaches to handle this, Pagination being most common.

Happy coding!

Answer 3

Assuming, the problem is properly stated:

As you probably understood, the idea is, I should be able to choose an item from itemList, select a country and the program should show me how much that specific item costs in that country. Now, I can use if statementand say something:

If you choose an item from an itemlist, you should already have it's index (let's call it item) in that list.

The same should apply for country (but call the index country).

Now you might have a maybe sparse 2-dim array of prices (called prices), then you could say:

/* datatype of price is left out as a different discussion, might be long
 for penny or cent or float for learning purpose or BigDecimal for bigger prieces. 
*/
price = prices[country][item];

If the prices are stored in a Map, maybe you can query it the same way, maybe by country name, item name. As long as we don't know, we can only guess.

price= prices.get ("US" + ":" + "Java-Compiler"); 

Maybe the prices are in a database, so you would need to query that.