组合模式(Composite Pattern)将对象组合成树形结构以表示“部分-整体”的层次结构。组合模式使得用户可以使用一致的方法操作单个对象和组合对象。
组合关系与聚合关系的区别:
(1)组合关系 - 在古代皇帝三宫六院,贵妃很多,但是每一个贵妃只属于皇帝。
(2)聚合关系 - 一个老师有很多学生,但是每一个学生又属于多个老师。
无涯教程通过以下示例演示复合模式的使用,在该示例中将显示组织的员工层次结构。
有一个 Employee 类,它充当组合模式参与者类。演示类将使用 Employee 类添加到部门级别并打印所有员工。
第1步 - 创建具有 Employee 对象列表的 Employee 类。
Employee.java
import java.util.ArrayList; import java.util.List; public class Employee { private String name; private String dept; private int salary; private List<Employee> subordinates; // constructor 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; } public String toString(){ return ("Employee :[ Name : " + name + ", dept : " + dept + ", salary :" + salary+" ]"); } }
第2步 - 使用 Employee 类创建和打印员工层次结构。
CompositePatternDemo.java
public class CompositePatternDemo { 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); } } } }
第3步 - 验证输出。
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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