Java常用设计模式————组合模式

引言

组合模式，是一种类似递归算法的结构性设计模式，通过以简单的 List ，组合本类对象，实现树状对象结构的“部分、整体”的层次。

它可以让调用程序不需要关心复杂对象与简单对象的区别，而统一地实现处理逻辑。

对于个体与整体存在一定共性的数据场景的展示非常有帮助，比如省市区的树状结构，领导与员工、校院系等。

一、组合模式的类图结构

用套娃形容组合模式非常贴切，其编码核心其实就是用数组来组合下级对象，而下级对象本身也属于此类实例。一般就是用于描述某种极具共性的实体类，如省、市、区；领导、员工等。

二、组合模式的代码实现

package com.mht.demo.组合模式;import java.util.ArrayList;
import java.util.List;public class Employee {private String name;private String dept;private int salary;/** 通过数组组合自身对象*/private List<Employee> subordinates;public Employee(String name, String dept, int salary) {this.name = name;this.dept = dept;this.salary = salary;this.subordinates = new ArrayList<>();}public void add(Employee emp) {this.subordinates.add(emp);}public void remove(Employee emp) {this.subordinates.remove(emp);}public List<Employee> getSubordinates() {return subordinates;}@Overridepublic String toString() {return "{\"name\":\"" + name + "\", \"dept\":\"" + dept + "\", \"salary\":\"" + salary + "\", \"subordinates\":"+ subordinates + "}";}
}

测试代码：

public class Client {public static void main(String[] args) {// 最上层员工，同时也是最高领导Employee ceo = new Employee("马云", "CEO", 30000);// 中层员工，同时也是中层领导Employee headSales = new Employee("Robert", "销售部", 20000);Employee headMarketing = new Employee("Michel", "市场部", 20000);// 基层员工，奋斗在业务一线Employee salesEmp = new Employee("Richard", "销售部", 10000);Employee salesEmp2 = new Employee("Rob", "销售部", 10000);Employee marketEmp = new Employee("Laura", "市场部", 10000);Employee marketEmp2 = new Employee("Bob", "市场部", 10000);ceo.add(headSales);ceo.add(headMarketing);headSales.add(salesEmp);headSales.add(salesEmp2);headMarketing.add(marketEmp);headMarketing.add(marketEmp2);// 打印CEO的管理层级System.out.println("CEO的管理层级：" + ceo);for (Employee headEmp : ceo.getSubordinates()) {System.out.println(headEmp);for (Employee subEmp : headEmp.getSubordinates()) {System.out.println(subEmp);}}}
}

测试结果：

CEO的管理层级：{"name":"马云", "dept":"CEO", "salary":"30000", "subordinates":[{"name":"Robert", "dept":"销售部", "salary":"20000", "subordinates":[{"name":"Richard", "dept":"销售部", "salary":"10000", "subordinates":[]}, {"name":"Rob", "dept":"销售部", "salary":"10000", "subordinates":[]}]}, {"name":"Michel", "dept":"市场部", "salary":"20000", "subordinates":[{"name":"Laura", "dept":"市场部", "salary":"10000", "subordinates":[]}, {"name":"Bob", "dept":"市场部", "salary":"10000", "subordinates":[]}]}]}
{"name":"Robert", "dept":"销售部", "salary":"20000", "subordinates":[{"name":"Richard", "dept":"销售部", "salary":"10000", "subordinates":[]}, {"name":"Rob", "dept":"销售部", "salary":"10000", "subordinates":[]}]}
{"name":"Richard", "dept":"销售部", "salary":"10000", "subordinates":[]}
{"name":"Rob", "dept":"销售部", "salary":"10000", "subordinates":[]}
{"name":"Michel", "dept":"市场部", "salary":"20000", "subordinates":[{"name":"Laura", "dept":"市场部", "salary":"10000", "subordinates":[]}, {"name":"Bob", "dept":"市场部", "salary":"10000", "subordinates":[]}]}
{"name":"Laura", "dept":"市场部", "salary":"10000", "subordinates":[]}
{"name":"Bob", "dept":"市场部", "salary":"10000", "subordinates":[]}

格式化后的结果：

{"name":"马云","dept":"CEO","salary":"30000","subordinates":[{"name":"Robert","dept":"销售部","salary":"20000","subordinates":[{"name":"Richard","dept":"销售部","salary":"10000","subordinates":[]},{"name":"Rob","dept":"销售部","salary":"10000","subordinates":[]}]},{"name":"Michel","dept":"市场部","salary":"20000","subordinates":[{"name":"Laura","dept":"市场部","salary":"10000","subordinates":[]},{"name":"Bob","dept":"市场部","salary":"10000","subordinates":[]}]}]
}