java设计模式之访问者（二）内嵌式访问者

内嵌式访问者模式

就是一棵树上的所有节点都有一个visit方法，每个父节点定义子节点的访问顺序。

因为访问逻辑都在节点内部，得名内嵌式访问者

下面展示一个demo，家谱是典型的树状结构，爷爷下面又爸爸和叔叔，爸爸下面又我和兄弟，依次访问。

public abstract class Node {
   abstract void visit();
}


@Data
@NoArgsConstructor
public class GrandFather {
    
    private Father father;
    private Uncle uncle;

    public GrandFather(Father father, Uncle uncle) {
        this.father = father;
        this.uncle = uncle;
    }
    
    public void visit() {
        System.out.println("I am GrandFather!");
        father.visit();
        uncle.visit();
    }
}

@Data
@NoArgsConstructor
public class Father extends Node {
    private Me me;
    private Brother brother;

    public Father(Me me, Brother brother) {
        this.me = me;
        this.brother = brother;
    }

    @Override
    void visit() {
        System.out.println("I am Father!");
        me.visit();;
        brother.visit();
    }
}


@AllArgsConstructor
@Data
public class Uncle extends Node {
    @Override
    void visit() {
        System.out.println("I am uncle!");
    }
}

@AllArgsConstructor
@Data
public class Me extends Node {
    @Override
    void visit() {
        System.out.println("I am me!");

    }
}

@Data
public class Brother extends Node {
    @Override
    void visit() {
        System.out.println("I am brother!");
    }
}

执行访问

public class App {
    public static void main(String[] args) {
        GrandFather grandFather = new GrandFather();
        Father father = new Father();
        Uncle uncle = new Uncle();
        Me me = new Me();
        Brother brother = new Brother();
        grandFather.setFather(father);
        grandFather.setUncle(uncle);
        father.setBrother(brother);
        father.setMe(me);
        grandFather.visit();

    }
}

展示结果

I am GrandFather!
I am Father!
I am me!
I am brother!
I am uncle!

这种内嵌式访问者模式业务逻辑和控制逻辑耦合在一起，在节点很多的时候修改维护都很困难，下面将介绍另外一种访问者模式