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) {}