Java常用设计模式————组合模式

喜欢ヅ旅行 2023-02-20 08:26 26阅读 0赞

# 引言 #

组合模式，是一种类似递归算法的结构性设计模式，通过以简单的 List ，组合本类对象，实现树状对象结构的“部分、整体”的层次。

它可以让调用程序不需要关心复杂对象与简单对象的区别，而统一地实现处理逻辑。

对于个体与整体存在一定共性的数据场景的展示非常有帮助，比如省市区的树状结构，领导与员工、校院系等。

# 一、组合模式的类图结构 #

用套娃形容组合模式非常贴切，其编码核心其实就是用数组来组合下级对象，而下级对象本身也属于此类实例。一般就是用于描述某种极具共性的实体类，如省、市、区；领导、员工等。

![watermark_type_ZmFuZ3poZW5naGVpdGk_shadow_10_text_aHR0cHM6Ly9ibG9nLmNzZG4ubmV0L3UwMTQ3NDUwNjk_size_16_color_FFFFFF_t_70][]

# 二、组合模式的代码实现 #

package com.mht.demo.组合模式;
    
    import java.util.ArrayList;
    import java.util.List;
    
    public class Employee {
    
    	private String name;
    	private String dept;
    	private int salary;
    	/** 通过数组组合自身对象*/
    	private List<Employee> subordinates;
    
    	public Employee(String name, String dept, int salary) {
    		this.name = name;
    		this.dept = dept;
    		this.salary = salary;
    		this.subordinates = new ArrayList<>();
    	}
    
    	public void add(Employee emp) {
    		this.subordinates.add(emp);
    	}
    
    	public void remove(Employee emp) {
    		this.subordinates.remove(emp);
    	}
    
    	public List<Employee> getSubordinates() {
    		return subordinates;
    	}
    
    	@Override
    	public String toString() {
    		return "{\"name\":\"" + name + "\", \"dept\":\"" + dept + "\", \"salary\":\"" + salary + "\", \"subordinates\":"
    				+ subordinates + "}";
    	}
    }

测试代码：

public class Client {
    	public static void main(String[] args) {
    		// 最上层员工，同时也是最高领导
    		Employee ceo = new Employee("马云", "CEO", 30000);
    		// 中层员工，同时也是中层领导
    		Employee headSales = new Employee("Robert", "销售部", 20000);
    		Employee headMarketing = new Employee("Michel", "市场部", 20000);
    		// 基层员工，奋斗在业务一线
    		Employee salesEmp = new Employee("Richard", "销售部", 10000);
    		Employee salesEmp2 = new Employee("Rob", "销售部", 10000);
    		Employee marketEmp = new Employee("Laura", "市场部", 10000);
    		Employee marketEmp2 = new Employee("Bob", "市场部", 10000);
    
    
    		ceo.add(headSales);
    		ceo.add(headMarketing);
    
    		headSales.add(salesEmp);
    		headSales.add(salesEmp2);
    
    		headMarketing.add(marketEmp);
    		headMarketing.add(marketEmp2);
    
    		// 打印CEO的管理层级
    		System.out.println("CEO的管理层级：" + ceo);
    		
    		for (Employee headEmp : ceo.getSubordinates()) {
    			System.out.println(headEmp);
    			for (Employee subEmp : headEmp.getSubordinates()) {
    				System.out.println(subEmp);
    			}
    		}
    	}
    }

测试结果：

CEO的管理层级：{"name":"马云", "dept":"CEO", "salary":"30000", "subordinates":[{"name":"Robert", "dept":"销售部", "salary":"20000", "subordinates":[{"name":"Richard", "dept":"销售部", "salary":"10000", "subordinates":[]}, {"name":"Rob", "dept":"销售部", "salary":"10000", "subordinates":[]}]}, {"name":"Michel", "dept":"市场部", "salary":"20000", "subordinates":[{"name":"Laura", "dept":"市场部", "salary":"10000", "subordinates":[]}, {"name":"Bob", "dept":"市场部", "salary":"10000", "subordinates":[]}]}]}
    {"name":"Robert", "dept":"销售部", "salary":"20000", "subordinates":[{"name":"Richard", "dept":"销售部", "salary":"10000", "subordinates":[]}, {"name":"Rob", "dept":"销售部", "salary":"10000", "subordinates":[]}]}
    {"name":"Richard", "dept":"销售部", "salary":"10000", "subordinates":[]}
    {"name":"Rob", "dept":"销售部", "salary":"10000", "subordinates":[]}
    {"name":"Michel", "dept":"市场部", "salary":"20000", "subordinates":[{"name":"Laura", "dept":"市场部", "salary":"10000", "subordinates":[]}, {"name":"Bob", "dept":"市场部", "salary":"10000", "subordinates":[]}]}
    {"name":"Laura", "dept":"市场部", "salary":"10000", "subordinates":[]}
    {"name":"Bob", "dept":"市场部", "salary":"10000", "subordinates":[]}

格式化后的结果：

{
        "name":"马云",
        "dept":"CEO",
        "salary":"30000",
        "subordinates":[
            {
                "name":"Robert",
                "dept":"销售部",
                "salary":"20000",
                "subordinates":[
                    {
                        "name":"Richard",
                        "dept":"销售部",
                        "salary":"10000",
                        "subordinates":[
    
                        ]
                    },
                    {
                        "name":"Rob",
                        "dept":"销售部",
                        "salary":"10000",
                        "subordinates":[
    
                        ]
                    }
                ]
            },
            {
                "name":"Michel",
                "dept":"市场部",
                "salary":"20000",
                "subordinates":[
                    {
                        "name":"Laura",
                        "dept":"市场部",
                        "salary":"10000",
                        "subordinates":[
    
                        ]
                    },
                    {
                        "name":"Bob",
                        "dept":"市场部",
                        "salary":"10000",
                        "subordinates":[
    
                        ]
                    }
                ]
            }
        ]
    }

# 总结 #

组合模式的使用场景非常特定，一般就是在输出打印树状结构型数据时才会用到。

它模糊了简单元素和复杂元素的概念，客户端程序可以像处理简单元素一样来处理复杂元素，从而使客户端与复杂元素的内部结构解耦。

定义时，通过List组织自身对象。同时也并未用到抽象类或接口。

注意为数组提供必要的添加和移除方法。

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