CSCI261E/F Lecture 19: Classes & Objects November 1, 2010 ? - - PowerPoint PPT Presentation

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*

• Ape
• Person
• Yuppie
• ColdHeartedExecutiveRobot
• Cyborg

* aka Object

What is a Thing?

Properties

• Height
• Width
• Depth
• Material Type
• Style
• Price
• Location

Table

• Height
• Width
• Depth
• Material Type
• Style
• Price
• Location

Chair

Behavior

• Support ____
• cup
• candle
• person
• etc

Table Chair

• Support ____
• person
• bag
• whoopee

cushion

• etc

Composition

• Consists of ____
• Table
• Chair
• Chair
• Chair

Dining Set “has a”

Inheritance

Piece Of Furniture

• Height
• Width
• Depth
• Material Type

Table Chair Bed Desk DiningTable NightStand “is a”

Program w/ a ‘Table’

int main() { int height = 3; int width = 6; int depth = 2; string material = “wood”; mytable = new Table(height, width, material); cout << table.width << endl; cout << table.height << endl; cout << table.material << endl; return 0; }

Instantiate a new Table object for me Call it mytable. A table object has properties. You access object properties with the ‘dot’ operator.

Dot-This, Dot-That

string name = clown.name; int age = clown.age; clown.name = “Homie”; clown.juggle(); clown.tell_joke(joke); access assignment functions

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

class Table { private: const int MAX_THINGS = 10; string on_the_table[MAX_THINGS] = {“”}; public: int height, width, length; double price; string material_name; bool support(string item_name); };

“Computer, a Table is a thing.” “It has a height, width and length.” “It has a price.” “It is made of some kind of material.” “It can support things (by name).”

Prototype or Interface in Table.h

Table Class

#include “Table.h” Table::support(string item_name) { for (int i = 0; i < MAX_THINGS; ++i) { if on_the_table[i] == “” {

• n_the_table[i] = item_name;

return true; } } return false; }

“Computer, a Table is a thing that is described in Table.h.” “I said it can support things, and here’s how.”

Implementation in Table.cpp

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); int depth(2); string material(“wood”); Table mytable(height, width, material); // ... return 0; }

Instantiate a new Table object for me and pass these values to the constructor function. Instantiate a new string object for me with the value “wood”

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