Visitor Pattern
Repressent an operation to be performed on the elements of an object structure.Visitor lets you define a new operation without changing the classees of the elements on which it operates.(封装一些作用于某种数据结构中的各种元素的操作，它能够在不改变数据结构的前提下定义作用于这些元素的新操作。)
直接上代码吧，心态不佳。
public abstract class Employee {
public final static int MALE=0;
public final static int FEMALE=1;
private String name;
private String salary;
private int sex;
public abstract void accept(IVisitor visitor); //allow a visitor
public String getName() {
return name;
}
public void setName(String name) {
this.name = name;
}
public String getSalary() {
return salary;
}
public void setSalary(String salary) {
this.salary = salary;
}
public int getSex() {
return sex;
}
public void setSex(int sex) {
this.sex = sex;
}
}
public class Manager extends Employee{
private String performance;
public String getPerformance() {
return performance;
}
public void setPerformance(String performance) {
this.performance = performance;
}
@Override
public void accept(IVisitor visitor) {
visitor.visit(this);
}
}public class CommonEmployee extends Employee{
private String job;
public String getJob() {
return job;
}
public void setJob(String job) {
this.job = job;
}
@Override
public void accept(IVisitor visitor) {
visitor.visit(this);
}
}public interface IVisitor {
public void visit(CommonEmployee commonEmployee);
public void visit(Manager manager);
}
真正的处理类在这里。
public class Visitor implements IVisitor {
public void visit(CommonEmployee commonEmployee) {
System.out.println(this.getCommonEmployee(commonEmployee));
}
public void visit(Manager manager) {
System.out.println(this.getManagerInfo(manager));
}
private String getBasicInfo(Employee employee) {
String info = "name:" + employee.getName() + " sex:"
+ (employee.getSex() == Employee.FEMALE ? "man" : "women")
+ " salary:" + employee.getSalary();
return info;
}
private String getManagerInfo(Manager manager) {
String basic = this.getBasicInfo(manager);
String otherInfo = " performance" + manager.getPerformance();
return basic + otherInfo;
}
private String getCommonEmployee(CommonEmployee commonEmployee){
String basic=this.getBasicInfo(commonEmployee)+" ";
String other="job:"+commonEmployee.getJob();
return basic+other;
}
}
測试
public class Client {
public static void main(String[] args) {
for(Employee e:mockEmployee()){
e.accept(new Visitor());
}
}
public static List<Employee> mockEmployee(){
List<Employee> list=new ArrayList<Employee>();
CommonEmployee zhangsan=new CommonEmployee();
zhangsan.setJob("coding everyday!");
zhangsan.setName("zhangsan");
zhangsan.setSalary("1800");
zhangsan.setSex(Employee.MALE);
CommonEmployee lirong=new CommonEmployee();
lirong.setJob("page coding,It's not fansion");
lirong.setName("lirong");
lirong.setSalary("1900");
lirong.setSex(Employee.FEMALE);
Manager wang=new Manager();
wang.setName("wamg");
wang.setPerformance("It's unpay basically,but he is a horser!");
wang.setSalary("10221");
wang.setSex(Employee.MALE);
list.add(zhangsan);
list.add(lirong);
list.add(wang);
return list;
}
}长处
● 符合单一职责原则
● 优秀的扩展性
● 灵活性很高
缺点
● 详细元素对訪问者发布细节
● 详细元素变更比較困难
● 违背了依赖倒置转原则
使用场景
● 一个对象结构包括非常多类对象，它们有不同的接口，而你想对这些对象实施一些依赖 于其详细类的操作。也就说是用迭代器模式已经不能胜任的情景。
● 须要对一个对象结构中的对象进行非常多不同而且不相关的操作，而你想避免让这些操 作“污染”这些对象的类。
扩展实例
1.统计功能
统计总工资total仅仅须要在IVisitor抽象中加入一个public int getTotalSalary();然后在详细訪问者中实现就可以。
public class Visitor implements IVisitor {
//部门经理的工资系数是5
private final static int MANAGER_COEFFICIENT = 5;
//员工的工资系数是2
private final static int COMMONEMPLOYEE_COEFFICIENT = 2;
//普通员工的工资总和
private int commonTotalSalary = 0;
//部门经理的工资总和
private int managerTotalSalary =0;
//计算部门经理的工资总和
private void calManagerSalary(int salary){
this.managerTotalSalary = this.managerTotalSalary + salary
*MANAGER_COEFFICIENT ;
}
//计算普通员工的工资总和
private void calCommonSlary(int salary){
this.commonTotalSalary = this.commonTotalSalary +
salary*COMMONEMPLOYEE_COEFFICIENT;
}
//获得全部员工的工资总和
public int getTotalSalary(){
return this.commonTotalSalary + this.managerTotalSalary;
}
}2.多个訪问者
由展示->汇总
IShowVisitor extends IVisitor
ITotalVisitor extends IVisitor
双分派
java的静态绑定和动态绑定。多态，重写，重载。
我是菜鸟，我在路上。