Relações (composição e agregação)

Abstract classes and interfaces
Sérgio Souza Costa
Universidade Federaldo Maranhão
28 de junho de 2016
Sérgio Souza Costa (Universidade Federaldo Maranhão) Paradigmas de Programação 28 de junho de 2016 1 / 17

Based in Dan Pilone. “UML 2.0 in a Nutshell.”

Summary
Association
Aggregation
Composition
Assignment

Dependency
The weakest relationship between classes, means that one class uses, or has knowledge of,
another class. It is typically a transient relationship, meaning a dependent class brieﬂy
interacts with the target class but typically doesn’t retain a relationship with it for any real
length of time.
Are typically read as "...uses a...”.For example, if you have a class named Window that
sends out a class named WindowClosingEvent when it is about to be closed, you would say
"Window uses a WindowClosingEvent.”
You show a dependency between classes using a dashed line with an arrow pointing from
the dependent class to the class that is used.

Association
Associations are stronger than dependencies and typically indicate that one class retains a
relationship to another class over an extended period of time.
Are typically read as "...has a...". For example, if you have a class named Window that
has a reference to the current mouse cursor, you would say "Window has a Cursor". .
You show an association using a solid line between the classes participating in the
relationship.

Navigability
“Associations have explicit notation to express navigability. If you can navigate from one
class to another, you show an arrow in the direction of the class you can navigate to. ”
“Because you can’t navigate from an instance of Cursor to an instance of Window, we
explicitly show the navigability arrow and an X where appropriate.”

Multiplicity
You can express how many instances of a particular class are involved in a relationship. I
You don’t specify a value, a multiplicity of 1 is assumed. To show a diﬀerent value, simply
place the multiplicity speciﬁcation near the owned class.

Example

Example - Item
public class Item {
...
public Item(int c, int q, float v, Produto p){
codigo =c;
qde = q;
valor = v;
prod = p;
}
public cal_valor(){
valor = qde * prog.get_preco();
}
}

Example - Produto
public class Produto {
private int codigo;
private String nome;
private float preco;
public Produto(int c, String n, float p){
codigo=c;
nome=n;
preco=p;
}
public double get_preco(){
return preco;
}
}

Example 2

Example 2 - Cliente
import java.util.Vector;
public class Cliente{
private String nome;
private String endereco;
private Vector ped;
public Cliente(String n,String e){
nome=n;
endereco=e;
ped=newVector();
}
public int get_size(){
return ped.size();
}

Example 2 - Cliente
public void add_pedido(Pedido p){ ped.addElement(p); }
public Pedido get_pedido(int i){ return (Pedido)ped.elementAt(i); }
public void exc_pedido(int id){
Pedido aux;
int tam=ped.size();
for(inti=0;i<tam;i++){
aux=(Pedido)ped.elementAt(i);
if(aux.get_id()==id){
ped.removeElementAt(i);
}
}
}}

Agregation
Is a stronger version of association. Unlike association, aggregation typically implies
ownership and may imply a relationship between lifelines.
Aggregations are usually read as "...owns a...". For example, if you had a classed named
Window that stored its position and size in a Rectangle class, you would say the "Window
owns a Rectangle.”
In the association example, Window doesn’t own the Cursor; Cursor was shared between
all applications in the system.”

Composition
Composition represents a very strong relationship between classes, to the point of
containment.
Composition is used to capture a whole-part relationship.
The lifetime of instances involved in composition relationships is almost always linked; if
the larger, owning instance is destroyed, it almost always destroys the part piece.

Composition and the design patterns
The Gang of Four suggests a few strategies for creating good object- oriented designs. In
particular, they suggest the following:
Design to interfaces.
Favor composition over inheritance
Find what varies and encapsulate it.

Assignment
Implementem as classes e suas relações como no diagrama abaixo.

Relações (composição e agregação)

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