Structural Patterns Part 3/7: Composite Pattern

Structural Patterns Part 3/7: Composite Pattern

目录

• • Structural Patterns Part 37 Composite Pattern
  • 目录
  • Definition
  • UML Class Diagram
  • Implementation

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Definition

Composite Pattern是这样一种模式：它把一系列对象组合起来，形成一个树状的结构来代表部分-整体(单个-组合)的关系，结构的每个元素都可以一视同仁，统一处理，有点递归的意思。

举个例子，在公司里，有CEO，Manager和Developer，Tester等职位。

CEO(单个)的下属是Manager(组合)，Manager(单个)的下属是Developer和Tester(组合)，但是对于Composite Pattern的使用者来说，不管是CEO还是Manager还是Developer还是Tester，他们都是Employee。

何时使用？当希望表示对象的部分-整体的结构时，当希望Client统一无差异的对待单个和组合对象。

使用频率： Medium High

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UML Class Diagram

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Implementation

把CEO, Manager以及Developer，Tester均看成Empolyee来处理。

// CompositeDemo
package designpatternsstructuralpatterns.composite;

import java.util.*;

public class CompositeDemo {
    public static void main(String[] args) {
        Employee CEO = new Employee("John", "CEO");
        Employee mgrDev = new Employee("Robert", "Dev Mgr");
        Employee mgrTest = new Employee("Michel", "Test Mgr");
        Employee dev1 = new Employee("Laura", "Dev");
        Employee dev2 = new Employee("Bob", "Dev");
        Employee test1 = new Employee("Richard", "Tester");
        Employee test2 = new Employee("Rob", "Tester");

        CEO.add(mgrDev);
        CEO.add(mgrTest);

        mgrDev.add(dev1);
        mgrDev.add(dev2);

        mgrTest.add(test1);
        mgrTest.add(test2);

        System.out.println(CEO);
        System.out.println("===============================");
        for (Employee manager : CEO.getSubordinates()) {
            System.out.println(manager);
            for (Employee employee : manager.getSubordinates()) {
                System.out.println(employee);
            }
            System.out.println("===============================");
        }
    }
}

class Employee {
    private String name;
    private String position;
    private List<Employee> subordinates;

    public Employee(String name, String position) {
        this.name = name;
        this.position = position;
        subordinates = new ArrayList<>();
    }

    public boolean add(Employee e) {
        return subordinates.add(e);
    }

    public boolean remove(Employee e) {
        return subordinates.remove(e);
    }

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

    @Override
    public String toString() {
        return "position: " + position + ", " + "name: " + name;
    }
}

// output 
position: CEO, name: John
===============================
position: Dev Mgr, name: Robert
position: Dev, name: Laura
position: Dev, name: Bob
===============================
position: Test Mgr, name: Michel
position: Tester, name: Richard
position: Tester, name: Rob
===============================