组合模式(Composite Pattern),又叫部分整体模式,是用于把一组相似的对象当作一个单一的对象。组合模式依据树形结构来组合对象,用来表示部分以及整体层次。这种类型的设计模式属于结构型模式,它创建了对象组的树形结构。
场景
- 维护和展示部分-整体关系
- 从一个整体中能独立出部分模块或功能
- 只要是树形结构,就应该考虑使用组合模式
实现
源码来自于菜鸟教程-设计模式
抽象构件
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+" ]");
}
}
使用示例
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);
}
}
}
}
优点
- 高层调用简单,一棵树中所有节点都是Component,局部和整理对调用者来说没有区别,高层代码不用关系自己处理的是单个对象还是整体结构
- 节点自由度增加,可以很方便的增加一个节点
缺点
- 与依赖倒置原则冲突
Android 中的应用
- View和ViewGroup
- 文件系统,文件和文件夹
参考
书籍:《设计模式之禅》、《Android源码设计模式》
技术文章:菜鸟教程-设计模式