JAVA设计模式——（二）组合模式

原理

组合模式用于描述对象在“整体-部分”中的关系，用户对单个对象和组合对象的使用具有一致性。

组合模式中由于单个对象和组合对象的使用具有一致性，所以需要定义组合对象中共有方法和属性，规范行为的接口。

解释

在组合模式中，整体与部分的关系，可以看成树形结构，一棵大树，有主干，有叶子。但是都是属于树的一部分，只不过叶子是附着在不同的枝干上面，枝杈又在主干上面。所以通过这种形式，便可以很快的构建出树状形式的结构。

最常见的例子，便是公司的结构。公司中有部门和员工，部门构成分支，员工是每个分支的节点，且部分隶属于公司。所以公司的结构信息是典型的组合模式。

实现

定义规范接口

规范接口用于统一各部分的行为。

package cn.sh.designepattern;import java.util.ArrayList;
import java.util.List;/*** @Author song* @Version 0.0.1* @Date 2025/4/22 14:48* @Contact [e-mail]*/
public interface Company {public void addComponent(Company company);public void removeComponent(Company company);public void getInfo();public List<Company> getComponents();
}

定义主干

package cn.sh.designepattern;import java.util.ArrayList;
import java.util.List;/*** @Author song* @Version 0.0.1* @Date 2025/4/22 15:02* @Contact [e-mail]*/
public class ActualCompany implements Company{private final List<Company> companies = new ArrayList<>();private String name;private String position;private int salary;public ActualCompany(String name, String position, int salary) {this.salary = salary;this.position = position;this.name = name;}@Overridepublic void addComponent(Company company) {companies.add(company);}@Overridepublic void removeComponent(Company company) {companies.remove(company);}@Overridepublic void getInfo() {System.out.println(this);}@Overridepublic List<Company> getComponents() {return companies;}@Overridepublic String toString() {return "Department{" +"companies=" + companies +", name='" + name + '\'' +", position='" + position + '\'' +", salary='" + salary + '\'' +'}';}
}

定义分支

package cn.sh.designepattern;import java.util.ArrayList;
import java.util.List;/*** @Author song* @Version 0.0.1* @Date 2025/4/22 14:51* @Contact [e-mail]*/
public class Department implements Company {private final List<Company> companies = new ArrayList<>();private String name;private String position;private int salary;public Department(String name, String position, int salary) {this.salary = salary;this.position = position;this.name = name;}@Overridepublic void addComponent(Company company) {companies.add(company);}@Overridepublic void removeComponent(Company company) {companies.remove(company);}@Overridepublic void getInfo() {System.out.println(this);}@Overridepublic List<Company> getComponents() {return companies;}@Overridepublic String toString() {return "Department{" +"companies=" + companies +", name='" + name + '\'' +", position='" + position + '\'' +", salary='" + salary + '\'' +'}';}
}

定义叶子

package cn.sh.designepattern;import java.util.ArrayList;
import java.util.List;/*** @Author song* @Version 0.0.1* @Date 2025/4/22 14:55* @Contact [e-mail]*/
public class Employee implements Company {private final List<Company> companies = new ArrayList<>();private String name;private String position;private int salary;public Employee(String name, String position, int salary) {this.name = name;this.position = position;this.salary = salary;}@Overridepublic void addComponent(Company company) {companies.add(company);}@Overridepublic void removeComponent(Company company) {companies.remove(company);}@Overridepublic void getInfo() {System.out.println(this);}@Overridepublic List<Company> getComponents() {return companies;}@Overridepublic String toString() {return "Employee{" +"companies=" + companies +", name='" + name + '\'' +", position='" + position + '\'' +", salary='" + salary + '\'' +'}';}
}

测试代码

package cn.sh.designepattern;/*** @Author song* @Version 0.0.1* @Date 2025/4/21 21:33* @Contact [e-mail]*/public class Main {public static void main(String[] args) {Company developDept = new Department("张三", "开发部主管", 10000);Company financeDept = new Department("张三", "财务部主管", 20000);Company saleDept = new Department("张三", "销售部主管", 30000);Company develop1 = new Employee("A", "开发部员工", 500);Company develop2 = new Employee("B", "开发部员工", 600);Company develop3 = new Employee("C", "开发部员工", 700);Company finance1 = new Employee("D", "财务部员工", 200);Company finance2 = new Employee("E", "财务部员工", 6500);Company finance3 = new Employee("F", "财务部员工", 700);Company sale1 = new Employee("G", "销售部员工", 1500);Company sale2 = new Employee("H", "销售部员工", 4600);Company sale3 = new Employee("I", "销售部员工", 5700);Company actualCompany = new ActualCompany("公司", "公司", 0);actualCompany.addComponent(developDept);actualCompany.addComponent(financeDept);actualCompany.addComponent(saleDept);developDept.addComponent(develop1);developDept.addComponent(develop2);developDept.addComponent(develop3);financeDept.addComponent(finance1);financeDept.addComponent(finance2);financeDept.addComponent(finance3);saleDept.addComponent(sale1);saleDept.addComponent(sale2);saleDept.addComponent(sale3);displayCompanyInfo(actualCompany);}private static void displayCompanyInfo(Company actualCompany) {actualCompany.getComponents().forEach(company -> {if (company instanceof Employee){company.getInfo();}else {company.getInfo();displayCompanyInfo(company);}});}
}

优势

组合模式适用于描述整体与部分之间的关系场景，对于上述的公司结构、文件夹结构等树形结构较有效，但是容易结构混乱，仅适用于结构简单的结构。