TransactionProcessor.java

public Transaction createTransaction(Sale sale, Customer customer) {
    Transaction transaction = new Transaction();
    populatePaymentDetails(transaction, sale, customer);
    populateCustomerDetails(transaction, customer);
    sale.setProcessed(true);
    return transaction;
}

private void populatePaymentDetails(Transaction transaction, Sale sale, Customer customer) {
    transaction.setPayerId(customer.getId());
    transaction.setCurrency(sale.getCurrency());
    transaction.setAmount(sale.getAmount());
}

private void populateCustomerDetails(Transaction transaction, Customer customer) {
    /** ... */
}