As mentioned, the scenario for the Accounts being subject for observation, and for Customer and alarm to be observers is that the bank on regular basis go through all its account to find if there has been any issue with the transactions on accounts. This may be that the transactions form a suspicious pattern, e.g. because the account has been hacked.
As a simple example we consider the case of money mules. A money mule is someone who transfers (typically illegally acquired) money on behalf of someone else. Money mules can move money in various ways, including through bank accounts.
Some money mules know they are supporting criminal enterprises; others are unaware that they are helping criminals profit.
Money mules often receive a commission for their service, or they might provide assistance because they believe they have a trusting or romantic relationship with the individual who is asking for help.
Acting as a money mule is illegal, therefore the customer is also included as an observer.
For the purpose of simplicity we assume that money muling takes place in one day, i.e. there is a deposit of a certain amount and a withdraw of the same amount on the same day. This activity may not be money muling, but it is still worth being reported as an issue. In real life banking there has to be a pattern of this pair of deposit/withdraw.
Account will for this purpose have the method checkTransactions that goes through all transactions on a given day and execute asSubject.notifyObservers for each occurrence of a deposit and withdraw of the same amount:
class Account(owner: ref Customer):
-"-
checkTransactions:
transactionsOfToday.scan
if (current.what = "deposit") :then
amount: var Real
amount := current.whichAmount
scanTail
if (current.what = "withdraw") :then
if (current.whichAmount = amount) :then
asSubject.notifyObserversThe method scanTail is defined in scan and iterates over the rest of the elements in the Set.
The Bank object (or some object within the Bank) calls this method every day for each Account object in the list of accounts:
...
theAccountsFile: obj OrderedList(#Account)
...
theAccountsFile.scan
current.checkTransactions The following Sequence Diagram shows the sequence of method calls for a partial run.
