M206 - TMA02 Question 2
(i) Screen capture.
(ii) The methods which make use of the pseudo-variable self are:- down, height.", hover: by: , initialize, and up. The
pseudo-variable super is only used in the initialize method.
(iii) The protocol of the Frog class is to be extended by the addition of a moveRight:
- moveRight: aNumber
"Set the receiver to move right by a given number (aNumber) of positions. Answer the receiver."
- self position:self position + aNumber.
(iv)The protocol of the HoverFrog class is to be extended by the addition of a new message above: for which the method heading and initial comment are as follows.
- above: aHoverfrog
"Increment the height of the receiver by one or more than the height of HoverFrog (an instance of HoverFrog or its subclasses). Answer the receiver."
- self height: ((self height) + 1)
(v) What is the message answer obtained from evaluating each of the following expressions?
(a) 3 + (2 * 4) message answer is 11. Smalltalk evaluates the bracketed part of the expression first (brackets take precedence).
(b) 3+ 2 * 4 message answer is 20. Smalltalk in this instance works through the expression from left o right.
(c) 3 plus: 2 * 4 message answer is 20. Smalltalk evaluates the expression to the right of the keyword plus: first then actions the keyword. In effect it is just another way of writing 3 + (2 * 4) as in part (a).