1. CMPE 135 Object-Oriented Analysis and Design March 7 Class Meeting
Department of Computer Engineering San Jose State University Spring 2019 Instructor: Ron Mak

2. Overloading vs. Overriding
Overloading is the ability to define multiple functions with the same name but with different formal parameters.
Parameters differ by number, datatype, or order.
Functions cannot differ only in return datatype.
Which function is called depends on the arguments.
Overriding is the ability of a member function of a subclass to redefine a member function in the superclass with the same signature (name, parameters, and return datatype).

3. Why Overload
Functions perform conceptually similar actions, differing only in their parameters.
Examples:
Functions perform the same action, only through different parameters.
Functions perform equivalent actions with different parameters.
void WriteInt(int value); // to standard out
void WriteInt(int value, File out);
void DrawDot(int x, int y);
void DrawDot(Point pt);
void WriteMessage(char *text);
void WriteMessage(string text);

4. Why Override
The subclass’s member function has the same signature as the superclass’s member function, but the subclass’s function must execute instead of the superclass’s function.

5. Why Override, cont’d Override.cpp class Employee { public:
    double pay() { return rate*hours; }
    
private:
    double rate;
    double hours; };
class Manager : public Employee
    double pay() {Employee::get_salary() + bonus; }
    double bonus;

6. Midterm Review
We looked at code that was functional but was inflexible and hard to maintain.
Code that was not able to handle change.
We incrementally improved the code.
Encapsulated what varied
Delegated tasks
Wrote code that could scale
In the process, we applied good object-oriented design principles.

7. Midterm Review, cont’d Understand what your customer wants.
Functional and nonfunctional requirements
UML diagrams: Use case, sequence, class
Functional Specification

8. Midterm Review, cont’d Analysis
Dealing with complexity.
Where do classes come from?
Textual analysis
CRC cards (Class Responsibility Collaboration)
Class relationships: dependency, inheritance, aggregation, composition
Design Specification
Design and implementation of the Day class

9. Midterm Review, cont’d Object-oriented design basics
Abstraction
Encapsulation
Inheritance
Polymorphism
Object-oriented design principles
Encapsulate what varies.
Favor composition over inheritance.
Code to interfaces, not implementations.

10. Midterm Review, cont’d Factory classes Accessors and mutators
Dangerous setters
Immutable classes
References to immutable objects

11. Midterm Review, cont’d Interfaces
Law of Demeter (“Principle of Least Knowledge”)
Liskov Substitution Principle
Cohesion
Completeness
Convenience
Clarity
Consistency

12. Midterm Review, cont’d Programming by contract
Precondition
Postcondition
Invariant
Favor composition over inheritance
Delegation
“Has a” vs. “is a”
SimUDuck example

13. Midterm Review, cont’d Polymorphism Rock-Paper-Scissors game
Abstract classes
Pure virtual member functions
Virtual destructors
Rock-Paper-Scissors game
Random choice
Simple machine learning

14. Midterm Format Canvas and the lockdown browser.
Multiple choice and short answer.
Write C++ code snippets.

15. Video
A typical requirements gathering meeting with customers.