M206 - TMA02 Question 1
- (i) An example of a keyword message selector from the protocol of numbers is plus: and one example of a binary message selector is +.
- (ii) A message that could be used to check if a string is a palindrome is: aString reverse
- (iii)
- (a) Order of evaluation a, b, c then d.
- (b) aNumber references the number object 3 after the evaluation of the expression series.
- (iv)
- (a) The purpose of the textual representation of a message answer is to communicate information about the message answer object to the user. The exact textual representation depends on what the programmer has designed into the object in question.
- (b)
|
message expression |
class of answer |
textual representation of answer |
|
myAccount holder |
ByteString |
'John Smith' |
|
myAccount balance |
SmallInteger |
100 |
(c) Write down an expression which when evaluated will produce a single line of text in the Display pane showing both the holder and the balance of the account referenced by myAccount;
(myAccount holder concatenate:(myAccount balance printString))
step |
receiver |
message |
message answer |
|
1 |
hisAccount |
balance: 100 |
an Account |
|
2 |
hisAccount |
credit: 20 |
an Account |
|
3 |
hisAccount |
balance |
120 |
|
4 |
herAccount |
balance: 120 |
an Account |
|
5 |
herAccount |
holder: 'Josephine Bloggs' |
an Account |
- vi) What are the final states of the objects referenced by slimey, croaker and hopper?
- This was diagram and has not been included - didn't scan well -sorry.
- The final states are..
|
Object |
colour |
position |
|
slimey |
Green |
5 |
|
croaker |
Brown |
5 |
|
hopper |
Green |
5 |