访问者模式(图)

访问者模式总结图如下(可点击放大)：

结构图：

 

示例：

public class VisitorTest {
    public static void main(String[] args) {
        ObjectStructure os = new ObjectStructure();
        os.add(new ConcreteElementA());
        os.add(new ConcreteElementB());
        Visitor visitor1 = new ConcreteVisitorA();
        os.accept(visitor1);
        System.out.println("------------------------");
        Visitor visitor2 = new ConcreteVisitorB();
        os.accept(visitor2);

    }
}

//抽象访问者
interface Visitor {
    void visit(ConcreteElementA element);
    void visit(ConcreteElementB element);
}

//具体访问A类
class ConcreteVisitorA implements Visitor {

    @Override
    public void visit(ConcreteElementA element) {
        System.out.println("具体访问者A访问 —>" + element.operationA());
    }

    @Override
    public void visit(ConcreteElementB element) {
        System.out.println("具体访问者A访问 —>" + element.operationB());
    }
}

//具体访问B类
class ConcreteVisitorB implements Visitor {

    @Override
    public void visit(ConcreteElementA element) {
        System.out.println("具体访问者B访问—>" + element.operationA());
    }

    @Override
    public void visit(ConcreteElementB element) {
        System.out.println("具体访问者B访问—>" + element.operationB());
    }
}


//抽象元素
interface Element {
    void accept(Visitor visitor);
}

//具体元素A类
class ConcreteElementA implements Element {

    @Override
    public void accept(Visitor visitor) {
        visitor.visit(this);
    }

    public String operationA() {
        return "具体元素A操作";
    }
}

//具体元素B类
class ConcreteElementB implements Element {

    @Override
    public void accept(Visitor visitor) {
        visitor.visit(this);
    }

    public String operationB() {
        return "具体元素B操作";
    }
}

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

    public void accept(Visitor visitor) {
        Iterator<Element> i = list.iterator();
        while (i.hasNext()) {
            i.next().accept(visitor);
        }
    }

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

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