设计模式-组合模式

定义

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。

用途

它在我们树型结构的问题中，模糊了简单元素和复杂元素的概念，客户程序可以像处理简单元素一样来处理复杂元素，从而使得客户程序与复杂元素的内部结构解耦。 以创建和打印员工的层次结构为例，最小单元示例：

1. 创建 Employee 类，该类带有 Employee 对象的列表。

public class Employee {

    private String name;
    // 部门
    private String dept;
    // 工资
    private int salary;
    // 员工 list
    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<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 +
                ", subordinates=" + subordinates +
                '}';
    }
}

2. 使用 Employee 类来创建和打印员工的层次结构。

final 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);

Log.e("---", ceo.toString());

// 打印
/*
 * Employee{name='John', dept='CEO', salary=30000,
 * subordinates=[Employee{name='Robert', dept='Head sales', salary=20000,
 * subordinates=[
 * Employee{name='Richard', dept='Sales', salary=10000, subordinates=[]},
 * Employee{name='Rob', dept='Sales', salary=10000, subordinates=[]}]},
 * Employee{name='Michel', dept='Head Marketing', salary=20000,
 * subordinates=[Employee{name='Laura', dept='Marketing', salary=10000, subordinates=[]},
 * Employee{name='Bob', dept='Marketing', salary=10000, subordinates=[]}]}]}
 */