CSCI261E/F Lecture 19: Classes & Objects November 1, 2010
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Programs & Things • Variables (ints, doubles, chars, etc) • Data Structures (arrays) • Things (strings, ...what else?)
Any Thing* * aka Object • Ape • Person • Yuppie • ColdHeartedExecutiveRobot • Cyborg
What is a Thing?
Properties Chair Table • Height • Height • Width • Width • Depth • Depth • Material Type • Material Type • Style • Style • Price • Price • Location • Location
Behavior Chair Table • Support ____ • Support ____ • cup • person • candle • bag • person • whoopee cushion • etc • etc
Composition “has a” Dining Set • Consists of ____ • Table • Chair • Chair • Chair
Inheritance “is a” Desk Table Piece Of Furniture • Height DiningTable Chair • Width NightStand Bed • Depth • Material Type
Program w/ a ‘Table’ int main() { int height = 3; int width = 6; int depth = 2; string material = “wood”; Instantiate a new Table object for me mytable = new Table(height, width, material); Call it mytable . cout << table.width << endl; cout << table.height << endl; A table object has properties. cout << table.material << endl; You access object properties with the ‘dot’ operator. return 0; }
Dot-This, Dot-That string name = clown.name; access int age = clown.age; assignment clown.name = “Homie”; clown.juggle(); functions clown.tell_joke(joke);
string Object string word = “revolution”; word.length(); Instantiate a string whose content is “revolution.” Call the string’s member function length() . (A function that belongs to an object.) (aka method)
So You Want a Table How can I create a table in my program? (instantiation) What does the table look like? (properties) How do I put stuff on the table? (behavior) Most importantly: How can I teach the computer what a table is? (?)
Declare a Table Class • A general description of what a table is • “furniture that can support things” • “has a width, height, depth” • “has some material type, like wood” • “costs money and has a price”
Table Class Prototype or Interface in Table.h class Table { “Computer, a Table is a thing.” private: const int MAX_THINGS = 10; string on_the_table[MAX_THINGS] = {“”}; public: “It has a height, width and length.” int height, width, length; “It has a price.” double price; string material_name; “It is made of some kind of material.” bool support(string item_name); “It can support things (by name).” };
Table Class Implementation in Table.cpp “Computer, a Table is a thing that is #include “Table.h” described in Table.h.” Table::support(string item_name) { for (int i = 0; i < MAX_THINGS; ++i) { “I said it can support things, and if on_the_table[i] == “” { here’s how.” on_the_table[i] = item_name; return true; } } return false; }
So You Want a Table How can I create a table in my program? (instantiation) What does the table look like? (properties) How do I put stuff on the table? (behavior) Most importantly: How can I teach the computer what a table is? (?)
Constructors • A special function • Named after the class name • Called automatically upon initialization
Using Constructors int main() { int height(3); int width(6); Instantiate a new string object for me with int depth(2); string material(“wood”); the value “wood” Instantiate a new Table object for me and pass Table mytable(height, width, material); these values to the constructor function. // ... return 0; }
Declaring Constructors • Declared in implementation file, with other functions • Must be named after the class • So the machine knows it’s a constructor
Example SolidBeginningsClass
Homework • Read 8.1 - 8.2, 8.4, 8.7 • Skip p361 “Initialization Lists” • Complete assignment SolidBeginningsClass
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