四、一個實際應用Visitor模式的例子
以下的例子演示了Employee對象集合允許被不同的Visitor（IncomeVisitor與VacationVisitor）訪問其中的內容。
// Visitor pattern -- Real World example
using System;
using System.Collections;
// "Visitor"
abstract class Visitor
{
// Methods
abstract public void Visit( Element element );
}
// "ConcreteVisitor1"
class IncomeVisitor : Visitor
{
// Methods
public override void Visit( Element element )
{
Employee employee = ((Employee)element);
// Provide 10% pay raise
employee.Income *= 1.10;
Console.WriteLine( "{0}'s new income: {1:C}",
employee.Name, employee.Income );
}
}
// "ConcreteVisitor2"
class VacationVisitor : Visitor
{
public override void Visit( Element element )
{
Employee employee = ((Employee)element);
// Provide 3 extra vacation days
employee.VacationDays += 3;
Console.WriteLine( "{0}'s new vacation days: {1}",
employee.Name, employee.VacationDays );
}
}
// "Element"
abstract class Element
{
// Methods
abstract public void Accept( Visitor visitor );
}
// "ConcreteElement"
class Employee : Element
{
// FIElds
string name;
double income;
int vacationDays;
// Constructors
public Employee( string name, double income,
int vacationDays )
{
this.name = name;
this.income = income;
this.vacationDays = vacationDays;
}
// PropertIEs
public string Name
{
get{ return name; }
set{ name = value; }
}
public double Income
{
get{ return income; }
set{ income = value; }
}
public int VacationDays
{
get{ return vacationDays; }
set{ vacationDays = value; }
}
// Methods
public override void Accept( Visitor visitor )
{
visitor.Visit( this );
}
}
// "ObjectStructure"
class Employees
{
// FIElds
private ArrayList employees = new ArrayList();
// Methods
public void Attach( Employee employee )
{
employees.Add( employee );
}
public void Detach( Employee employee )
{
employees.Remove( employee );
}
public void Accept( Visitor visitor )
{
foreach( Employee e in employees )
e.Accept( visitor );
}
}
/**//// <summary>
/// VisitorApp test
/// </summary>
public class VisitorApp
{
public static void Main( string[] args )
{
// Setup employee collection
Employees e = new Employees();
e.Attach( new Employee( "Hank", 25000.0, 14 ) );
e.Attach( new Employee( "Elly", 35000.0, 16 ) );
e.Attach( new Employee( "Dick", 45000.0, 21 ) );
// Create two visitors
IncomeVisitor v1 = new IncomeVisitor();
VacationVisitor v2 = new VacationVisitor();
// Employees are visited
e.Accept( v1 );
e.Accept( v2 );
}
}
