Summing transaction amounts by currency

import java.util.List;
import java.util.Map;
import java.util.stream.Collectors;

class Main {
    public static void main(String[] args) {
        /**
         * Scenario: I have a list of Transaction objects (id, amount, currency). 
         * I want you to sum the total amount for a specific currency (e.g., "USD"), 
         * but only for transactions over $1000.
         */
         List<Transaction> transactions = List.of(new Transaction(1, 1000.0, "USD"),
                new Transaction(2, 1900.0, "USD"),
                new Transaction(3, 3000.0, "EUR"),
                new Transaction(4, 2000.0, "EUR"),
                new Transaction(5, 100.0, "USD"),
                new Transaction(6, 1100.0, "EUR"),
                new Transaction(7, 5000.0, "MXN"));
                
        // We have a list of transactions. We need to sum the anount of the transactions by currency
        // but only taking into account the ones greater to $1000
        
        // We can collect them and use the groupingBy collector. Then we can use 
        // the filtering collector to filter transactions and only include 
        // with amount greater than 1000
        // Funally, we can pass the summingDouble downstream collector to summarize the 
        // amounts
        Map<String, Double> transactionsByCurrency = transactions.stream()
                .collect(Collectors.groupingBy(t -> t.currency(), Collectors.filtering(t -> t.amount() > 1000.0, Collectors.summingDouble(t -> t.amount()))));
                
        System.out.println(transactionsByCurrency);
    }
}

record Transaction(int id, double amount, String currency) {}