概念理解

组合模式用来表示整体和部分的结构，是一种结构型模式。对于客户端而言，整体和部分开放的是同一个接口，调用起来并没有不同。换种说法，一个对象和一组对象对于客户端而言，使用方式是一致的。

实例说明

组合模式的典型表示方式是树形结构，实例有很多，比如文件系统，网站菜单，公司和部门之间的关系，员工领导和下属的关系。现在考虑员工和下属的关系，实现起来非常简单:不管是领导还是员工，都使用同一个类雇员，雇员中有名字，薪水，部门，和管理的下属员工。底层员工的下属员工列表为空，并不影响调用。

public class Employee {

    private String name;
    private String dept;
    private int salary;
    private List<Employee> subordinate;

    public Employee(String name, String dept, int salary) {
        this.name = name;
        this.dept = dept;
        this.salary = salary;
        subordinate = new ArrayList<Employee>();
    }

    public String getName() {
        return name;
    }

    public void setName(String name) {
        this.name = name;
    }

    public String getDept() {
        return dept;
    }

    public void setDept(String dept) {
        this.dept = dept;
    }

    public int getSalary() {
        return salary;
    }

    public void setSalary(int salary) {
        this.salary = salary;
    }

    public List<Employee> getSubordinate() {
        return subordinate;
    }

    public void setSubordinate(List<Employee> subordinate) {
        this.subordinate = subordinate;
    }

    public void addEmployee(Employee e) {
        this.subordinate.add(e);
    }

    @Override
    public String toString() {
        return "name=" + name + ",dept=" + dept + ",salary=" + salary;
    }
}

public class App {
    public static void main(String[] args) {
        Employee chief = initEmployee();
        printEmployee(chief);

    }

    public static void printEmployee(Employee e){
        System.out.println(e.toString());
        List<Employee> subordinates = e.getSubordinate();
        for(int i =0;i<subordinates.size();i++){
            printEmployee(subordinates.get(i));
        }
    }

    public static Employee  initEmployee() {
        Employee chief = new Employee("SAM", "Finance", 10000);
        Employee leader = new Employee("tom", "Finance", 7000);
        Employee amy = new Employee("amy", "Finance", 4000);
        Employee sary = new Employee("sary", "Finance", 4000);
        chief.addEmployee(leader);
        chief.addEmployee(sary);
        leader.addEmployee(amy);
        return chief;
    }
}

代码实例参见：https://github.com/jxl198/designPattern/tree/master/composite