介紹
將對象組合成樹形結構以表示"部分-整體"的層次結構。組合模式使得用戶對單個對象和組合對象的使用具有一致性。
優點
1、高層模塊調用簡單。
2、節點自由增加。
缺點
在使用組合模式時,其葉子和樹枝的聲明都是實現類,而不是接口,違反了依賴倒置原則。
何時使用
1、想表示對象的部分-整體層次結構(樹形結構),如樹形菜單,文件、文件夾的管理。
2、您希望用戶忽略組合對象與單個對象的不同,用戶將統一地使用組合結構中的所有對象。
使用建議
它在我們樹型結構的問題中,模糊了簡單元素和複雜元素的概念,客戶程序可以像處理簡單元素一樣來處理複雜元素,從而使得客戶程序與複雜元素的內部結構解耦。
具體實現
類圖:
代碼:
package com.knowledge.system.software_design_pattern.composite_pattern;
import java.util.ArrayList;
import java.util.List;
public class Employee {
private String name;
private String dept;
private int salary;
private List <Employee> subordinates;
//構造函數
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+" ]");
}
}
package com.knowledge.system.software_design_pattern.composite_pattern;
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);
//打印該組織的所有員工
System.out.println(CEO);
for (Employee headEmployee : CEO.getSubordinates()) {
System.out.println(headEmployee);
for (Employee employee : headEmployee.getSubordinates()) {
System.out.println(employee);
}
}
}
}