Download C++ Class Review: Procedural & Data Abstraction with Product and Time Classes and more Study notes Humanities in PDF only on Docsity! Class review [Bono] 1 Review of classes • Review of procedural abstraction • Discovering classes • Example class definition • Information hiding (encapsulation) • Member function definitions * Product and Time examples and code are from Big C++, by Cay Horsmann and Timothy Budd; Wiley 2005 Class review [Bono] 2 Procedural abstraction • An example of a procedural abstraction: – interface: // reverseString: s’ has the same characters as // s, but with its characters in reverse order. void reverseString(string &s); – Possible implementations? Class review [Bono] 5 Data abstraction • Just like we can add operations with procedures, we can add user-defined data types, called abstract data types (or ADTs) • An ADT defines a set of possible values + a set of valid operations on the type. • Example: string – values are sequences of characters – operations are size, <, ==, =, +=, etc. • The language mechanism for ADTs in C++ is class – Function abstracts an action (operation) – Class abstracts a thing (object) Class review [Bono] 6 Discovering Classes • If program has a bunch of related variables that all refer to the same concept, think about the concept as a whole • Example from Big C++ – Computer has name, price, and score – Need to find model (out of a bunch of models) with highest score / price ratio (best value) – Code to do this with various data values: Requires 6 variables. (see bestval.cpp) – Better to abstract the concept: Product – Using Product class simplifies the program (see product1.cpp) Class review [Bono] 7 Discovering classes (cont.) • Now, suppose you need to sort all the computer data by value (i.e., score / price). • In old representation, instead of triplets of values now we would need three different vectors of values, and have to associate ones with same index: – E.g. name[i], score[i], price[i] • More natural to define one vector of Products. All the data about one product is in one element of the vector (i.e., one object). Class review [Bono] 10 Encapsulation • Information hiding – implementations of member functions not part of interface – also, data members are not part of interface. • Always put data in private section. • What is rationale? • Discuss with respect to an example class… Class review [Bono] 11 Time Class A class for representing a time of day (between 00:00:00 and 23:59:59). Code from Big C++ • Time t; Constructs time object "t" with the current time. • Time(hours, minutes, seconds) Constructs the time with hours, minutes, and secs. • t.get_seconds() Returns the seconds value of t. • t.get_minutes() Returns the minutes value of t. • t.get_hours() Returns the hours value of t. • t.add_seconds(n) Changes t to move by n seconds. n may be negative • t.seconds_from(t2) Computes the number of seconds between t and t2. Class review [Bono] 12 Why encapsulation? • Can guarantee that the object data cannot be put into an incorrect state. – E.g. can’t make a time with 25 hours in it by mistake: Time liftoff(19, 30, 0); . . . liftoff.hours = liftoff.hours + 6; // oops, not a legal time – In contrast: liftoff.add_seconds( 6*MIN_PER_HOUR*SEC_PER_MIN);
