设计模式之访问者模式

访问者模式

访问者模式UML.png

例子以公司招聘查看简历为背景

interface Visitor{
    void visitClerical(Clerical clerical);//查看文员简历
    void visitCoder(Coder coder);//查看程序员简历
}    

访问者接口，分别对ElementA与ElementB进行访问

class HRVisitor{
    public void visitClerical(Clerical clerical){
        //HR关注文员简历XXXXX
    }
    
    public void visitCoder(Coder coder){
        //HR看码农简历，看经验看学校
    }
}

HR访问者

class CTOVisitor{
    public void visitClerical(Clerical clerical){
        //CTO不关心文员简历，可是是空实现
    }
    
    public void visitCoder(Coder coder){
        //CTO看码农简历，看项目 看技能
    }
}

CTO访问者

abstract class JobSeeker{
    public String name;
    public String school;
    public String skill;
    
    public JobSeeker(String name ,String school ,String skill){
        this.name = name;
        this.school = school;
        this.skill = skill;
    }
    
    public abstract void accept(Visitor visitor);
}

抽象求职者类

class Clerical extends JobSeeker{
    public Clerical(String name ,String school ,String skill){
        super(name , school , skill);
    }
    public void accept(Visitor visitor){
        visitor.visitClerical(this);
    }
}

文员求职者

class Coder extends JobSeeker{
    public Coder(String name ,String school ,String skill){
        super(name , school , skill);
    }
    public void accept(Visitor visitor){
        visitor.visitCoder(this);
    }
}

码农求职者

public class JobStructure{
    List<JobSeeker> list = new ArrayList<>();
    
    public void seeResume(Visitor visitor){
        for(JobSeeker jobSeeker : list){
            jobSeeker.accept(visitor);
        }
    }
    
    public void addJobSeeker(JobSeeker jobSeeker){
        list.add(jobSeeker);
    }
}   

查阅简历类

class CLient{
    public static void main(String[] args){
        JobStructure jobStructure = new JobStructure();
        jobStructure.addJobSeeker(new Coder("小强","清华","Android"));
        jobStructure.addJobSeeker(new Coder("小民","北大","Word"));
        jobStructure.seeResume(new CTOVisitor());
        jobStructure.seeResume(new HRVisitor());
    }
}   

客户端类，收集简历，CTO查看简历，HR查看简历