Aula 06 - Composição e Herança

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Projeto de Software / P3 
Composição e Herança 
Márcio Ribeiro 
marcio@ic.ufal.br 
twitter.com/marciomribeiro 
Composi'on	
  
3 
ShoppingCart…	
  
§  …	
  has	
  a	
  list	
  of	
  products	
  
ShoppingCart!
- customerID : int"
- productList : ArrayList"
+ addProduct() : void"
+ removeProduct() : void"
+ getContents() : String"
+ getCustomerID() : int"
+ getItemCount() : int"
+ getTotalPrice() : double"
Product!
- name : String"
- price : double"
+ getName() : String"
+ getPrice() : double"
n 
4 
Composi'on	
  
§  “has-­‐a”	
  rela'onship	
  
§  Code	
  reuse	
  
§  Example:	
  
§  ArrayList	
  
§  List	
  of	
  our	
  shopping	
  cart	
  products	
  
Now,	
  let’s	
  improve	
  our	
  
E-­‐commerce	
  applica'on!	
  
6 
E-­‐commerce	
  products	
  
7 
TV	
  
§  Implement	
  the	
  following	
  TV	
  class	
  
TV!
- brand : String"
- price : double"
- inches : int"
+ getBrand() : String"
+ getPrice() : double"
+ getInches(): int"
8 
Refrigerator	
  
§  Now,	
  implement	
  this	
  one:	
  
Refrigerator!
- brand : String"
- price : double"
- size : int"
+ getBrand() : String"
+ getPrice() : double"
+ getSize(): int"
9 
Stove	
  
§  Finally,	
  this	
  one:	
  
Stove!
- brand : String"
- price : double"
- burners : int"
+ getBrand() : String"
+ getPrice() : double"
+ getBurners(): int"
10 
Keep	
  in	
  mind	
  that…	
  
§  SoLware	
  changes	
  all	
  the	
  'me!	
  
§  “80%	
   of	
   the	
   life'me	
   cost	
   of	
   a	
   piece	
   of	
   soLware	
   goes	
   to	
  
maintenance”	
  
§  Change	
  requests!	
  
§  You	
  need	
  to	
  be	
  prepared	
  
§  Avoid	
  error-­‐prone	
  tasks	
  
§  Improve	
  produc'vity	
  
§  Improve	
  'me-­‐to-­‐market	
  	
  
From	
  http://www.oracle.com/technetwork/java/codeconv-­‐138413.html	
  
11 
Change	
  request	
  
§  CR:	
  we	
  need	
  to	
  debit	
  the	
  IPI	
  tax	
  for	
  all	
  products	
  
12 
Change	
  request	
  scaUered	
  throughout	
  the	
  classes…	
  
TV!
- brand : String"
- price : double"
- inches : int"
+ getBrand() : String"
+ getPrice() : double"
+ getInches(): int"
Refrigerator!
- brand : String"
- price : double"
- size : int"
+ getBrand() : String"
+ getPrice() : double"
+ getSize(): int"
Stove!
- brand : String"
- price : double"
- burners : int"
+ getBrand() : String"
+ getPrice() : double"
+ getBurners(): int"
What	
  is	
  going	
  on?	
  
Error-prone 
Low productivity 
Time consuming 
14 
What	
  are	
  the	
  commonali'es?!	
  
TV!
- brand : String"
- price : double"
- inches : int"
+ getBrand() : String"
+ getPrice() : double"
+ getInches(): int"
Refrigerator!
- brand : String"
- price : double"
- size : int"
+ getBrand() : String"
+ getPrice() : double"
+ getSize(): int"
Stove!
- brand : String"
- price : double"
- burners : int"
+ getBrand() : String"
+ getPrice() : double"
+ getBurners(): int"
What	
  is	
  going	
  on?	
  
Cloned code: no reuse 
16 
In	
  our	
  e-­‐commerce	
  applica'on…	
  
§  What	
  are	
  TV,	
  Refrigerator,	
  and	
  Stove?!	
  
PRODUCTS!	
  
No'ce	
  that	
  this	
  is	
  common	
  
in	
  real	
  life!	
  
18 
Generaliza'on	
  versus	
  Specializa'on	
  
Sp
ec
ia
liz
at
io
n 
G
eneralization 
Vehicle Car Race car 
Ophthalmologist Person Doctor 
19 
Commonali'es	
  
§  They	
  all	
  have:	
  
§  Brand	
  
§  Price	
  
This	
  is	
  general	
  for	
  
all	
  products	
  
Move	
  the	
  common…	
  
Product!
- brand : String"
- price : double"
+ getBrand() : String"
+ getPrice() : double"
So, move the common attributes and methods 
to the Product class… 
Common	
  aUributes	
  in	
  the	
  Product	
  class…	
  
Product!
- brand : String"
- price : double"
+ getBrand() : String"
+ getPrice() : double"
TV!
- inches : int"
+ getInches(): int"
Refrigerator!
- size : int"
+ getSize(): int"
Stove!
- burners : int"
+ getBurners(): int"
… and keep the variabilities in each specialized class 
Inheritance	
  
23 
Inheritance	
  
§  Mechanism	
  to	
  
§  Organize	
  informa'on	
  
§  Achieve	
  categoriza'on	
  
§  Group	
  and	
  modeling	
  similari'es	
  among	
  classes	
  
§  Create	
  a	
  taxonomy	
  of	
  objects	
  
§  Hierarchy	
  tree	
  
§  “is-­‐a”	
  rela'onship	
  
§  TV	
  is	
  a	
  product	
  
§  Refrigerator	
  is	
  a	
  product	
  
§  Stove	
  is	
  a	
  product	
  
24 
Superclass	
  
package br.ufal.ic.ecommerce.product;	
	
public class Product {	
	
 private String brand; 		
 private double price;	
	
 public Product(String brand, double price) {	
 this.brand = brand;	
 this.price = price;	
 }	
 	
 public String getBrand() {	
 return brand;	
 }	
 	
 public double getPrice() {	
 return price;	
 }	
}	
25 
Subclass	
  
package br.ufal.ic.ecommerce.product;	
	
public class TV extends Product {	
	
 private int inches;	
	
 public TV(String brand, double price, int inches) {	
 super(brand, price);	
 this.inches = inches;	
 }	
	
 public int getInches() {	
 return inches;	
 }	
		
}	
26 
Back	
  to	
  the	
  change	
  request	
  
§  CR:	
  we	
  need	
  to	
  debit	
  the	
  IPI	
  tax	
  for	
  all	
  products	
  
Common	
  aUributes	
  in	
  the	
  Product	
  class…	
  
Product!
- brand : String"
- price : double"
+ getBrand() : String"
+ getPrice() : double"
TV!
- inches : int"
+ getInches(): int"
Refrigerator!
- size : int"
+ getSize(): int"
Stove!
- burners : int"
+ getBurners(): int"
Now, only one class needs changing! 
28 
Reasons	
  to	
  use	
  inheritance	
  
§  BeUer	
  modularity	
  
	
  
§  Separa'on	
  of	
  concerns	
  
§  Categoriza'on	
  
§  Clear	
  representa'on	
  of	
  concepts