什么是组合模式？

组合模式又叫部分整体模式，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。
简单说就是：用树结构组织对象，把多个对象当成一个对象使用。

适用场景

可以用树结构表示的业务场景，比如所有的组织结构，行政区划等等

代码实现

示例：一个公司的组织结构就是Tree结构，用组合模式展示

//示例：公司的组织架构
/**
 * 员工类
 */
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;
    }
    @Override
    public String toString() {
        return ("Employee :[ Name : " + name
                + ", dept : " + dept + ", salary :"
                + salary + " ]");
    }
}
/**
 * 组合模式测试
 */
public class CompositePattern {
    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 ]
    }
}

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