设计模式之访问者模式——初学

package com.zcr.vistor;

public abstract class Element
{
    public abstract void Accept(Vistor vistor);
}

package com.zcr.vistor;

public class ConcreteElementA extends Element
{
    
    //充分利用双分派技术，实现处理与数据结构的分离
    @Override
    public void Accept(Vistor vistor)
    {
        vistor.VistConcreteElementA(this);

    }
    
    public void OperationA()
    {
        
    }

}

package com.zcr.vistor;

public class ConcreteElementB extends Element
{

    @Override
    public void Accept(Vistor vistor)
    {
        vistor.VistConcreteElementB(this);
        
    }
    
    public void OperationB()
    {
        
    }
    

}

package com.zcr.vistor;

public abstract class Vistor
{
    public abstract void VistConcreteElementA(ConcreteElementA concreteElementA);
    public abstract void VistConcreteElementB(ConcreteElementB concreteElementB);
}

package com.zcr.vistor;

public class ConcreteVistor1 extends Vistor
{

    @Override
    public void VistConcreteElementA(ConcreteElementA concreteElementA)
    {
        System.out.println(concreteElementA.getClass().getName()+"被"+this.getClass().getName()+"访问");
        
    }

    @Override
    public void VistConcreteElementB(ConcreteElementB concreteElementB)
    {
        System.out.println(concreteElementB.getClass().getName()+"被"+this.getClass().getName()+"访问");
        
    }
    
}

package com.zcr.vistor;

public class ConcreteVistor2 extends Vistor
{
    @Override
    public void VistConcreteElementA(ConcreteElementA concreteElementA)
    {
        System.out.println(concreteElementA.getClass().getName()+"被"+this.getClass().getName()+"访问");
        
    }

    @Override
    public void VistConcreteElementB(ConcreteElementB concreteElementB)
    {
        System.out.println(concreteElementB.getClass().getName()+"被"+this.getClass().getName()+"访问");
        
    }
}

package com.zcr.vistor;

import java.util.ArrayList;
import java.util.List;

public class ObjectStructure
{
    private List<Element> elements = new ArrayList<Element>();
    
    public void Attach(Element element)
    {
        elements.add(element);
    }
    
    public void Detach(Element element)
    {
        elements.remove(element);
    }
    
    public void Accept(Vistor vistor)
    {
        for(Element e : elements)
        {
            e.Accept(vistor);
        }
    }
    
}

package com.zcr.vistor;

public class VistorTest
{
    public static void main(String[] args)
    {
        ObjectStructure o = new ObjectStructure();
        o.Attach(new ConcreteElementA());
        o.Attach(new ConcreteElementB());
        
        ConcreteVistor1 v1= new ConcreteVistor1();
        ConcreteVistor2 v2= new ConcreteVistor2();
        
        o.Accept(v1);
        o.Accept(v2);
    }
}