访问者模式(Visitor)

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本文详细介绍了UML类图的概念及其在实际编程中的应用，并通过Python代码实例展示了如何实现类图中的组件与访问者模式。文章旨在帮助开发者理解和实践面向对象设计中的关键概念。

UML类图

代码实现

    public abstract class Visitor
    {
        public abstract void VisitComponentA(Component component);
        public abstract void VisitComponentB(Component component);
    }

    public abstract class Component
    {
        public abstract void Receive(Visitor visitor);
    }

    public class ComponentA : Component
    {
        public override void Receive(Visitor visitor)
        {
            visitor.VisitComponentA(this);
        }
    }

    public class ComponentB : Component
    {
        public override void Receive(Visitor visitor)
        {
            visitor.VisitComponentB(this);
        }
    }

    public class Manager
    {
        public List<Component> components = new List<Component>();

        public void Receive(Visitor visitor)
        {
            foreach (var component in components)
            {
                component.Receive(visitor);
            }
        }
    }

Python代码实现

class Visitor(object):
    def VisitA(self, component):
        raise NotImplementedError("abstract")
    def VisitB(self):
        raise NotImplementedError("abstract")

class Visitor1(Visitor):
    def VisitA(self, component):
        print "this is visitor1 which is visiting "+component.name+" now."
    def VisitB(self, component):
        print "this is visitor1 which is visiting "+component.name+" now."

class Visitor2(Visitor):
    def VisitA(self, component):
        print "this is visitor2 which is visiting "+component.name+" now."
    def VisitB(self, component):
        print "this is visitor2 which is visiting "+component.name+" now."

class Component(object):
    name=""
    def Receive(self, visitor):
        raise NotImplementedError("abstract")

class ComponentA(Component):
    def __init__(self):
        self.name="ComponentA"
    def Receive(self, visitor):
        visitor.VisitA(self)

class ComponentB(Component):
    def __init__(self):
        self.name="ComponentB"
    def Receive(self, visitor):
        visitor.VisitB(self)

class ComponentManager(object):
    components=[ComponentA(),ComponentB()]
    def Receive(self, visitor):
        for component in self.components:
            component.Receive(visitor)

if __name__ == "__main__":
    manager=ComponentManager()
    
    visitor1=Visitor1()
    visitor2=Visitor2()
    manager.Receive(visitor1)
    manager.Receive(visitor2)