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CSE 2221 Exam Study Guide | Study Questions with 100% Correct Verified Answers
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CSE 2221 Exam Study Guide | Study Questions with 100% Correct Verified Answers
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CSE 2221 Exam Study Guide | StudyQuestions with 100% Correct Verified
Answers
Parameter Modes - ANSWER There are 4 parameter modes, each of which indicates a
possible way that a method might change the value of the corresponding argument.
Parameter modes help in 3 ways:
1) concisely summarize which arguments might have their values modified by a call
2) make requirements/ensures clauses shorter
3) alllow us to perform sanity checks of contracts against simple errors
Repeated Arguments - ANSWER The reciever is an argument: the reference value of the
reciever of a call (to an instance method) is copied to the formal parameter of this. Hence,
there is a repeated argument if the reciever is also passed as another argument to such a call.
Never pass any variable of a mutable reference type as an argument twice or more to a
single method call.
Clears Mode - ANSWER Upon return from a method call, a clear-mode parameter has an initial
value for its type, i.e., a value that an assignment of the no-argument constructor could give it.
This is equivalent to adding "and = [an initial value for its type] to the ensures clause]. A
clears-mode parameter should not appear in the ensures clause except as #x
, Restores Mode - ANSWER Upon return from a method call, a restores-mode parameter once
again has its incoming value. Equivalent to adding, e.g., ...and x = #x to the ensures clauss. An
old restores-mode parameter, e.g. #x should not appear in the ensures clause. This is the
default parameter mode, so if a parameter is not listed with some other mode then its mode
is restores.
Parameter Passing: References vs Parameters - ANSWER Just as the assignment operator copies
reference values, parameter passing to method calls copies reference values. The reference
values of the arguments are copied into the formal parameters to initialize them at the time of
the call. Upon return, nothing is copied back except the returned value of the method (if any),
and here too the reference value is coped back.
Equality Checking: References vs Parameters - ANSWER Just as the assignment operator =
copies reference values, and parameter passing to method calls copies reference values, the
equality operator == compares reference values. Since comparing object values is often what
you want instead, the equals method compares object values.
Aliasing - ANSWER When 2 reference variables contain the same reference value i.e.
two triangles pointing to the same oval, or one object with 2 references to it
Distinguished Formal Parameter - ANSWER Instance methods are called as follows:
n.methodName(arguments)
n is reciever; for all instance methods, the corresponding distinguished formal
parameter implicitly has the name this
Reciever - ANSWER Instance methods are called as follows: n.methodName(arguments).
Where n is called the reciever
Object value - ANSWER The object value is the mathematical model value of the object
the reference points to
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