结构型（六） - 组合模式

一、概念

组合模式（Composite Pattern）：将对象组合成树形结构以表示“部分-整体”的层次结构。组合模式使得用户对单个对象和组合对象的使用具有一致性。

使用场景：组合结构不常用，需要部分与整体的层次关系为树形结构，并且部分与整体的对象是能让客户端能统一对待、不需区分的对象，例如：文件管理系统，在遍历查找的时候，文件和文件夹对我们来说不做区分，可以做到逻辑统一。

二、实现

这里借鉴参考文章公司和职员的例子，公司的组织结构包含部门和员工两种数据类型。其中，部门又可以包含子部门和员工。然后通过构建树形结构来遍历计算公司总的工资支出成本。

1、定义公司及员工的父类HumanResource，用来统一处理薪资计算。

public abstract class HumanResource { protected long id; protected double salary; public HumanResource(long id) { this.id = id; } public long getId() {return id; } public abstract double calculateSalary();
}

2、员工和部门

#Employee 
public class Employee extends HumanResource { public Employee(long id, double salary) {super(id); this.salary = salary;} @Override public double calculateSalary() {return salary; }
}#Department 
public class Department extends HumanResource { private List<HumanResource> subNodes = new ArrayList<>();public Department(long id) { super(id); } @Override public double calculateSalary() {double totalSalary = 0;if (subNodes.size() <= 0) {return 0;}for (HumanResource hr : subNodes) { totalSalary += hr.calculateSalary(); } this.salary = totalSalary; return totalSalary;} public void addSubNode(HumanResource hr) {subNodes.add(hr);}
}

3、我们建立一个树形部门架构，如下图：
组合树形结构.PNG

测试类

public class Client {public static void main(String[] args) {Department department = new Department(0);Department departmentA = new Department(1);Department departmentA1 = new Department(2);Department departmentB = new Department(3);Department departmentB1 = new Department(4);Employee employee0 = new Employee(0,50000);Employee employee1 = new Employee(1,8000);Employee employee2 = new Employee(2,8000);Employee employee3 = new Employee(3,4000);Employee employee4 = new Employee(4,4000);department.addSubNode(departmentA);department.addSubNode(departmentB);department.addSubNode(employee0);departmentA.addSubNode(employee1);departmentA.addSubNode(departmentA1);departmentB.addSubNode(employee2);departmentB.addSubNode(departmentB1);departmentA1.addSubNode(employee3);departmentB1.addSubNode(employee4);double salary = department.calculateSalary();System.out.println("公司工资开支：" + salary);}
}