设计模式之访问者模式

public interface Visitor {
    public void visitElementA(ConcreteElementA concreteElementA);

    public void visitElementB(ConcreteElementB concreteElementB);
}

public class ConcreteVisitorOne implements Visitor {
    @Override
    public void visitElementA(ConcreteElementA concreteElementA) {
        System.out.println(this.getClass().getSimpleName() + "访问" + concreteElementA.getClass().getSimpleName());
    }

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

public class ConcreteVisitorTwo implements Visitor {
    @Override
    public void visitElementA(ConcreteElementA concreteElementA) {
        System.out.println(this.getClass().getSimpleName() + "访问" + concreteElementA.getClass().getSimpleName());
    }

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

public interface Element{
    public void accept(Visitor visitor);
}

public class ConcreteElementA implements Element{
    @Override
    public void accept(Visitor visitor) {
        visitor.visitElementA(this);
    }
}

public class ConcreteElementB implements Element{
    @Override
    public void accept(Visitor visitor) {
        visitor.visitElementB(this);
    }
}

public class Component {
    private List<Element> list = new ArrayList<>();

    public void add(Element element) {
        list.add(element);
    }

    public void delete(Element element) {
        list.remove(element);
    }

    public void accept(Visitor visitor) {
        for (Element element : list) {
            element.accept(visitor);
        }
    }
}

public class VisitorDemo{
    public static void main(String[] args) {
        Component component = new Component();
        component.add(new ConcreteElementA());
        component.add(new ConcreteElementB());

        ConcreteVisitorOne visitorOne = new ConcreteVisitorOne();
        ConcreteVisitorTwo visitorTwo = new ConcreteVisitorTwo();

        component.accept(visitorOne);
        component.accept(visitorTwo);
    }
}