kahoot-challenge-2025/src/Main.java

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

public class Main {
	public static void main(String[] args) {
		// Get the data from the file
		List<String> data = ReadFile.open("test.txt");
		
		// Gets a map with the total occurrences for each domain
		Map<String, Integer> domains = getDomainTotal(data);
		
		System.out.println(domains);
	}

	/**
	 * Totals up the amount of times an email domain occured in the list. 
	 * @param emails A list of emails
	 * @return A map of email domains and the total amount of times they occured in the <code>emails</code> parameter
	 */
	private static Map<String, Integer> getDomainTotal(List<String> emails) {
		// Create a map of all email address domains and counting them
		Map<String, Integer> domains = new HashMap<>();
		for (String email : emails) {
			if (!EMail.validate(email)) {
				throw new IllegalArgumentException("There was an invalid email in the file!");
			}

			String domain = EMail.getDomain(email);

			// Add email domain to the list
			if (!domains.containsKey(domain)) {
				// Creates new entry in the map if the domain didn't exist before
				domains.put(domain, 1);
			} else {
				// Updates the map with the new total for the domain
				// Gets the old total and adds 1
				Integer newTotal = domains.get(domain) + 1;

				// Update domain value with new total
				domains.replace(domain, newTotal);
			}
		}
		
		return domains;
	}
}