Solving a Parallel Streams Puzzler

ParallelStreamsPuzzler.java

import java.util.List;
import java.util.stream.LongStream;

import static java.util.stream.Collectors.toList;

public class ParallelStreamsPuzzler {

    public static void main(String[] args) {
        List<Transaction> transactions
                = LongStream.rangeClosed(0, 1_000)
                            .mapToObj(Transaction::new)
                            .collect(toList());

        Account myAccount = new Account();
        // bug
        transactions.parallelStream()
                    .forEach(myAccount::process);

        System.out.println("The total balance is " + myAccount.getAvailableAmount());
    }


    static class Account {
        private long total = 0;
        public void process(Transaction transaction) {
            add(transaction.getValue());
        }
        public void add(long amount) {
            total += amount;
        }

        public long getAvailableAmount(){
            return total;
        }
    }

    static class Transaction {
        private final long value;
        public Transaction(long value) {
            this.value = value;
        }
        public long getValue() {
            return value;
        }
    }
}