行为型模式 --- 访问者模式

package study.org;

public class Demo {
    public static void main(String[] args) {
        Visitor visitor = new MyVisitor();  
        Subject sub = new MySubject();  
        sub.accept(visitor);
    }
}

interface Visitor {
    public void visit(Subject sub);
}

interface Subject {
    public void accept(Visitor visitor);

    public String getProperty();
}

class MyVisitor implements Visitor {
    @Override
    public void visit(Subject sub) {
        System.out.println(sub.getProperty());
    }
}

class MySubject implements Subject {
    @Override
    public void accept(Visitor visitor) {
        visitor.visit(this);
    }
    
    @Override
    public String getProperty() {
        return "property value";
    }
}