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The total sum of canceled transactions

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Let's say you are developing a banking system. There are two classes in this system:

  • Transaction with the fields uuid (String), the State enum (CANCELED, FINISHED, PROCESSING), sum (Long)
  • Account with the fields number (String), balance (Long), and transactions (List<Transaction>)

Both classes have getters for all fields with the corresponding names (getState(), getSum(), getTransactions() and so on).

Using Stream API, implement a method that calculates the total sum of canceled transactions for all non-empty accounts (balance > 0). Perhaps, flatMap method can help you to implement it.

Important. Use the given template for your method. Pay attention to the type of argument and the returned value. Please, use only the Stream API without loops.

Examples: there are 2 accounts (in JSON notation) below. The result is 10 000.

[
  {
    "number": "1001",
    "balance": 0,
    "transactions": [
      {
        "uuid": "774cedda-9cde-4f53-8bc2-5b4d4859772a",
        "state": "CANCELED",
        "sum": 1000,
      }
    ]
  },
  {
    "number": "1002",
    "balance": 8000,
    "transactions": [
      {
        "uuid": "337868a7-f469-43c0-9042-3422ce37ee26a",
        "state": "FINISHED",
        "sum": 8000,
      },
      {
        "uuid": "f8047f86-89e7-4226-8b75-74c55a4d7e31",
        "state": "CANCELED",
        "sum": 10000,
      }
    ]
  }
]
Write a program in Java 17
import java.util.*;

class TransactionExample {

/**
* Calculates the general sum of canceled transactions for all non empty accounts in the list
*/
public static long calcSumOfCanceledTransOnNonEmptyAccounts(List<Account> accounts) {
// write your code here
}

// Don't change the code below
public static void main(String[] args) {

Scanner scanner = new Scanner(System.in);

int numberOfAccounts = Integer.parseInt(scanner.nextLine());
List<Account> accounts = new ArrayList<>();

for (int i = 0; i < numberOfAccounts; i++) {
String[] accDesc = scanner.nextLine().split(" ");
String number = accDesc[0];
Long balance = Long.parseLong(accDesc[1]);

int numberOfTransByAccount = Integer.parseInt(scanner.nextLine());
List<Transaction> trans = new ArrayList<>();

for (int j = 0; j < numberOfTransByAccount; j++) {
String[] transDesc = scanner.nextLine().split(" ");
String uuid = transDesc[0];
State state = convertStringToState(transDesc[1]);
Long sum = Long.parseLong(transDesc[2]);
trans.add(new Transaction(uuid, state, sum));
}

accounts.add(new Account(number, balance, trans));
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