Description
Question 1:
Java (as well as C and C++) allows comments delimited by “/*” and “*/”. This kind of comment can be defined
in English as follows:
A comment consists of three parts:
1. a slash followed by a star, followed by
2. the body of the comment, followed by
3. a star followed by a slash.
The body of the comment can be empty, or can contain any characters except the two-character sequence “*/”.
Note that the body of a comment can include stars and slashes, just not “*/”.
Assume that the following JLex macros have been defined:
SLASH = [/]
STAR = [*]
Label each of the following JLex patterns as being correct/incorrect for the type of the comment described
above.
1. {SLASH}{STAR}[^(*/)]*{STAR}{SLASH}
2. {SLASH}{STAR}(.)*{STAR}{SLASH}
3. {SLASH}{STAR}([^*]*{STAR}+[^*/])*{STAR}+{SLASH}
4. {SLASH}{STAR}([^*]|[^/])+{STAR}{SLASH}
5. {SLASH}{STAR}[^*]*{STAR}+{SLASH}+
6. {SLASH}{STAR}([^*]|({STAR}+[^*/]))*{STAR}+{SLASH}
For each incorrect pattern, explain what is wrong. For example, you might say The pattern does not allow the
comment body to include stars, or The pattern does allow the comment body to include */.
If the pattern both disallows some “good” comments and allows some “bad” comments, give two explanations,
one for each problem with the pattern.
Then, for each problem with the pattern, give a string that illustrates the problem; i.e., give a string that is not
matched by the pattern but is a “good” comment and/or give a string that is matched by the pattern but is a “bad”
comment.
Be sure that it is clear whether your example strings are intended to be “good” or “bad” comments.
Question 2:
In class, we looked at JLex, a scanner generator that produces Java code given a specification. Here is a simple
application of JLex. Imagine that there is a time-intensive function myFunc that you are allowed to use only a
limited number of times, due to performance concerns. A scanner can count the number of calls to this function.
Your task is to write a JLex specification that would generate this scanner.
You should fill in this PDF appropriately and upload it for the solution.
Here are the specifications
The scanner should print the line number every time it encounters a call to myFunc .
The scanner should finally print the total number of calls to myFunc .
You can assume that the source file to be scanned is in Java. (This defines the format for function calls).
There may potentially be other variables named myFunc. There may also be other functions that contain
myFunc in their names.
However, you can assume that the declaration/definition of myFunc is not present in the source file to be
scanned – only calls to myFunc are present.
You do not know the return type of myFunc. So, it may appear anywhere in a statement. This might seem
odd since you usually know the return type if you know the name of the function. But by assuming that
any return type is possible, you generate a more generic scanner.