lecture 37: proxy pattern

LECTURE 37:PROXY PATTERN

Computer Science 313 – Advanced Economic Topics

Is This a Check or Money?

Currency issued by Bank of the United States Once we figure that out: how much was

it worth?

Silver Standard Is Best

While now illegal, how much was this worth?

Silver Standard Is Best

While now illegal, how much was this worth? WHY?

Other Currency Standard

What was value of these denominations? Notes on gold standard used by banks in

late 30s

Other Currency Standard

What was value of these denominations? Federal reserve note from early 30s

How Much Is This Worth?

How Much Is This Worth?

When ordering online, pay $0.0259 per check Under $0.01 of pen ink used on the

check At cheapest, check worth little over 3.5

cents $0.15/check for really fancy ones I

found Would need to supply your name &

address Bank name & account number needed

for this too

Generous Offer

Following offer open to all students in class:

I will trade $0.16 for your next signed paycheck

My offer is VERY serious with contract ready Probably not high quality, expensive

type of check Without additional value, you will end up

richer

Why Not?

Why Not?

Patterns In Real-Life

Usually worth more than their components They are both implementations of proxy

pattern Checks are remote proxies, but in the

real-world See working of virtual proxy with old U.S.

currency Consider definition of the word

"Proxy"Ally or friend whom you give power

to work as if they were you;Agent;

Substitute

Remote Proxy in Action

Signed check is deposited into your account Client sees bank give them cash, but more

needed To get cash, bank must follow several

steps Image of useless paper made at local bank

branch Bank then has image sent to local

clearinghouse Request routed to source bank for approval Other bank has check amount deducted

from account Approval sent to clearinghouse as electronic

transfer Clearinghouse has result sent back to your

bank

Remote Proxy Example

YouYourBank

Clearing-house

OtherBank

Remote Proxy Example

YouYourBank

Clearing-house

OtherBank

Remote Proxy Picture

Virtual Proxy

Silver & gold standard currency virtual proxies Bills still (nearly) worthless paper & ink

creation Fed reserve banks kept vaults of gold and

silver Trade for bill for gold/silver at any of these

banks This is simpler proxy, no 3rd party needed!You Ban

kVault

For Next Class

Lab updated soon with Final info Will run office hours during time scheduled for

exam Last design pattern reading continues for

Monday