設計模式 - 組合模式

組合模式用於我們需要以類似於單個物件的方式處理一組物件的情況。組合模式將物件組合成樹形結構，以表示部分以及整體層次結構。這種設計模式屬於結構模式，因為它建立了物件組的樹形結構。

這種模式建立一個包含其自身物件組的類。此類提供修改其相同物件組的方法。

我們將透過以下示例演示組合模式的使用，在該示例中，我們將展示組織的員工層次結構。

實現

我們有一個`Employee`類，它充當組合模式參與者類。我們的演示類`CompositePatternDemo`將使用`Employee`類來新增部門級別層次結構並列印所有員工。

步驟1

建立包含`Employee`物件列表的`Employee`類。

Employee.java

import java.util.ArrayList;
import java.util.List;

public class Employee {
   private String name;
   private String dept;
   private int salary;
   private List<Employee> subordinates;

   // constructor
   public Employee(String name,String dept, int sal) {
      this.name = name;
      this.dept = dept;
      this.salary = sal;
      subordinates = new ArrayList<Employee>();
   }

   public void add(Employee e) {
      subordinates.add(e);
   }

   public void remove(Employee e) {
      subordinates.remove(e);
   }

   public List<Employee> getSubordinates(){
     return subordinates;
   }

   public String toString(){
      return ("Employee :[ Name : " + name + ", dept : " + dept + ", salary :" + salary+" ]");
   }   
}

步驟2

使用`Employee`類建立並列印員工層次結構。

CompositePatternDemo.java

public class CompositePatternDemo {
   public static void main(String[] args) {
   
      Employee CEO = new Employee("John","CEO", 30000);

      Employee headSales = new Employee("Robert","Head Sales", 20000);

      Employee headMarketing = new Employee("Michel","Head Marketing", 20000);

      Employee clerk1 = new Employee("Laura","Marketing", 10000);
      Employee clerk2 = new Employee("Bob","Marketing", 10000);

      Employee salesExecutive1 = new Employee("Richard","Sales", 10000);
      Employee salesExecutive2 = new Employee("Rob","Sales", 10000);

      CEO.add(headSales);
      CEO.add(headMarketing);

      headSales.add(salesExecutive1);
      headSales.add(salesExecutive2);

      headMarketing.add(clerk1);
      headMarketing.add(clerk2);

      //print all employees of the organization
      System.out.println(CEO); 
      
      for (Employee headEmployee : CEO.getSubordinates()) {
         System.out.println(headEmployee);
         
         for (Employee employee : headEmployee.getSubordinates()) {
            System.out.println(employee);
         }
      }		
   }
}

步驟3

驗證輸出。

Employee :[ Name : John, dept : CEO, salary :30000 ]
Employee :[ Name : Robert, dept : Head Sales, salary :20000 ]
Employee :[ Name : Richard, dept : Sales, salary :10000 ]
Employee :[ Name : Rob, dept : Sales, salary :10000 ]
Employee :[ Name : Michel, dept : Head Marketing, salary :20000 ]
Employee :[ Name : Laura, dept : Marketing, salary :10000 ]
Employee :[ Name : Bob, dept : Marketing, salary :10000 ]