设计模式-组合模式

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博客介绍了组合模式，将对象组合成树形结构表示“部分 - 整体”层次结构，使用户对单个和组合对象的使用一致。还给出例子，定义员工类，包含下属员工列表，从CEO开始打印下属列表可遍历人员信息。

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💬定义

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。

😀例子

源自（https://www.runoob.com/design-pattern/composite-pattern.html）
📝定义一个员工类，有一个下属员工的列表，类型同样是员工类。

public class Employee {
   private String name;
   private String dept;
   private int salary;
   private List<Employee> subordinates;
 
   //构造函数
   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+" ]");
   }   
}

📝测试类

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);
 
      //打印该组织的所有员工
      System.out.println(CEO); 
      for (Employee headEmployee : CEO.getSubordinates()) {
         System.out.println(headEmployee);
         for (Employee employee : headEmployee.getSubordinates()) {
            System.out.println(employee);
         }
      }        
   }
}

🎥 输出：

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 ]

从CEO开始打印下属员工列表就可以遍历整个人员信息。