访问者设计模式

访问者设计模式：
##被访问者：
有一些稳定的结构对象，提供accept方法供访问者进行访问

##访问者：
一些访问者，有一个visitor方法实现对对象的访问，不同的对象会做出不同的反应！

##应用
公司年终奖考核：
被访问者有：程序员，产品经理（accept(Visitor)）
访问者：CEO，CTO(visit(…))
CEO可能只会关注KPI，CTO可能只会关注程序员的KPI+代码量，产品经理的KPI+产品数量
不同访问对象对被访问对象的访问可能产生不同的结果！

##实现

`
public interface Visitor {

void visit(Manager manager);
void visit(Engineer engineer);

}

public class CEOVisitor implements Visitor {
@Override
public void visit(Manager manager) {
System.out.println("manager kpi “+manager.getKpi()+” products "+manager.getProducts());
}

@Override
public void visit(Engineer engineer) {
    System.out.println("engineer kpi "+engineer.getKpi());
}

}

public class CTOVisitor implements Visitor {
@Override
public void visit(Manager manager) {
System.out.println("manager kpi “+manager.getKpi()+” products "+manager.getProducts());
}

@Override
public void visit(Engineer engineer) {
    System.out.println(" engineer kpi "+engineer.getKpi()+"  products "+engineer.getCodeLine());
}

}

public abstract class Staff {

private String kpi;

public String getKpi() {
    return kpi;
}

public void setKpi(String kpi) {
    this.kpi = kpi;
}

protected abstract void accept(Visitor visitor);

}

public class Engineer extends Staff {

public Engineer() {
    setKpi("1.0");
}



public int getCodeLine() {
    return new Random(100).nextInt();
}

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

}

public class Manager extends Staff {

public Manager() {
    setKpi("3.0");
}



public int getProducts() {
    return new Random(1000).nextInt();
}

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

}

public class BusinessReport {
private Visitor visitor;
private List staffList = new ArrayList<>();
public BusinessReport() {
staffList.add(new Engineer());
staffList.add(new Engineer());
staffList.add(new Manager());
staffList.add(new Manager());
}

public void showReport(Visitor visitor) {
    this.visitor = visitor;
    visitAll();
}
public void visitAll() {
    for (Staff staff:staffList) {
        staff.accept(visitor);
    }
}

public class Test {

public static void main(String[] args) {
    BusinessReport businessReport = new BusinessReport();
    System.out.println("CEO-------------------");
    CEOVisitor ceoVisitor = new CEOVisitor();
    businessReport.showReport(ceoVisitor);
    System.out.println("CEO-------------------");

    System.out.println("CTO-------------------");
    CTOVisitor ctoVisitor = new CTOVisitor();
    businessReport.showReport(ctoVisitor);
    System.out.println("CTO-------------------");
}

}

`

##类结构图