Visitor Pattern - Customers Report - Java Sourcecode
Java Source Code Example for the Visitor Design Pattern - implementation version without reflection
Main.java - The Main class is the client object. It has a reference tot the Object structure. In our case the objects Structure is the Customers objects
package com.oodesign.designpatterns.behavioral.visitor.impl;
package com.oodesign.designpatterns.behavioral.visitor.customers;
public class Main {
/**
* @param args
*/
public static void main(String[] args) {
// TODO Auto-generated method stub
Customer c = new Customer("customer1");
c.addOrder(new Order(".order1", "..item1"));
c.addOrder(new Order(".order2", "..item1"));
c.addOrder(new Order(".order3", "..item1"));
Customer c2 = new Customer("customer2");
Order o = new Order(".order_a");
o.addItem(new Item("..item_a1"));
o.addItem(new Item("..item_a2"));
o.addItem(new Item("..item_a3"));
c2.addOrder(o);
c2.addOrder(new Order(".order_b", "..item_b1"));
CustomerGroup customers = new CustomerGroup();
customers.addCustomer(c);
customers.addCustomer(c2);
GeneralReport visitor = new GeneralReport();
customers.accept(visitor);
visitor.displayResults();
}
} |
IVisitor and IVisitable interfaces
package com.oodesign.designpatterns.behavioral.visitor.customers;
public interface IVisitable {
public void accept(IVisitor visitor);
}
|
package com.oodesign.designpatterns.behavioral.visitor.customers;
public interface IVisitor {
public void visit(Customer customer);
public void visit(Order order);
public void visit(Item item);
} |
GeneralReport is a visitor class and implements the IVisitor interface. Other Visitors (other reports or other types of visitors) can be added by implementing the IVisitor interface
package com.oodesign.designpatterns.behavioral.visitor.customers;
public class GeneralReport implements IVisitor{
private int customersNo;
private int ordersNo;
private int itemsNo;
public void visit(Customer customer)
{
System.out.println(customer.getName());
customersNo ++;
}
public void visit(Order order)
{
System.out.println(order.getName());
ordersNo++;
}
public void visit(Item item)
{
System.out.println(item.getName());
itemsNo++;
}
public void displayResults()
{
System.out.println("Nr of customers:" + customersNo);
System.out.println("Nr of orders: " + ordersNo);
System.out.println("Nr of itemss: " + itemsNo);
}
}
|
CustomerGroup, Customer, Order and Item are all visitable classes. A CustomerGroup represents a group of customers, each Customer can have one or more orders and each order can have one ore more Items.
package com.oodesign.designpatterns.behavioral.visitor.customers;
import java.util.ArrayList;
import java.util.Iterator;
public class CustomerGroup {
private ArrayList customers = new ArrayList();
public void accept(IVisitor visitor)
{
for (Iterator it=customers.iterator(); it.hasNext();)
{
((Customer)it.next()).accept(visitor);
}
}
public void addCustomer(Customer customer)
{
customers.add(customer);
}
} |
package com.oodesign.designpatterns.behavioral.visitor.customers;
import java.util.ArrayList;
import java.util.Iterator;
public class Customer implements IVisitable{
private String name;
private ArrayList orders = new ArrayList();
public void accept(IVisitor visitor)
{
visitor.visit(this);
for (Iterator it=orders.iterator(); it.hasNext();)
{
((IVisitable)it.next()).accept(visitor);
}
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public void addOrder(Order order)
{
orders.add(order);
}
public Customer(String name)
{
this.name = name;
}
} |
package com.oodesign.designpatterns.behavioral.visitor.customers;
import java.util.ArrayList;
import java.util.Iterator;
public class Order implements IVisitable {
private String name;
private ArrayList items = new ArrayList();
public Order(String name)
{
this.name = name;
}
public Order(String name, String itemName)
{
this.name = name;
this.addItem(new Item(itemName));
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public void accept(IVisitor visitor)
{
visitor.visit(this);
for (Iterator it=items.iterator(); it.hasNext();)
{
((Item)it.next()).accept(visitor);
}
}
public void addItem(Item item)
{
items.add(item);
}
} |
package com.oodesign.designpatterns.behavioral.visitor.customers;
public class Item implements IVisitable{
private String name;
public void accept(IVisitor visitor)
{
visitor.visit(this);
}
public Item(String name)
{
this.name = name;
}
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
} |
Behavioral Patterns 
