组合模式用于需要以同样的方式的方式处理一组对象作为单个对象。组合模式根据树结构组成对象，以表示部分以及整个层次结构。这种类型的设计模式属于结构模式，因为此模式创建了一组对象的树结构。
此模式创建一个包含其自身对象的组的类。 此类提供了修改其相同对象的组的方法。
我们通过以下示例展示组合模式的使用，将演示员工组织的层次结构。
实现实例
假设有一个类Employee，它作为复合模式操作类。 CompositePatternDemo这是一个演示类，将使用Employee类添加部门级别层次结构并打印所有员工。组合模式示例结构如下图中所示 -
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类来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);
//print all employees of the organization
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，执行上面的代码得到以下结果 -
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 ]
