組合模式主要是為了表達(dá)“部分-整體”的層次結(jié)構(gòu)，例如公司的組織架構(gòu)，每個(gè)部門下又有若干個(gè)下級(jí)部門，再如菜單結(jié)構(gòu)，每個(gè)菜單下可能有一個(gè)或多個(gè)子菜單。

下例以員工的層級(jí)結(jié)構(gòu)說明組合模式的用法。每個(gè)員工都有姓名、部門、工資等屬性，每個(gè)員工可能有0個(gè)或多個(gè)下屬員工。

Employee類的代碼如下：

复制package composite;


import java.util.ArrayList;
import java.util.List;


public class Employee {
  private String name;
  private String department;
  private int salary;
  private List < Employee > subordinates;
  //構(gòu)造函數(shù)
  public Employee(String name, String department, int salary) {
    this.name=name;
    this.department=department;
    this.salary=salary;
    this.subordinates=new ArrayList < Employee > ();
  }
  //添加下屬
  public void add(Employee employee) {
    subordinates.add(employee);
  }
  //移除下屬
  public void remove(Employee employee) {
    subordinates.remove(employee);
  }
  //獲取下屬
  public List < Employee > getSubordinates(){
    return subordinates;
  }
  //轉(zhuǎn)成字符串
  public String toString() {
    return "員工（姓名："+name+"，部門："+department+"，工資："+salary+"）";
  }
}

主函數(shù)調(diào)用方式：

复制package main;
import composite.*;


public class CompositePattern {
  public static void main(String[] args) {
    //創(chuàng)建一個(gè)員工：總裁
    Employee president = new Employee("李剛","管理層",30000);
    //創(chuàng)建兩個(gè)員工：部門領(lǐng)導(dǎo)
    Employee directorSales = new Employee("王孟","銷售部",20000);
    Employee directorRND = new Employee("嚴(yán)明","研發(fā)部",20000);
    //創(chuàng)建兩個(gè)員工：銷售部銷售員
    Employee saler1 = new Employee("孟德貴","銷售部",10000);
    Employee saler2 = new Employee("肖亮高","銷售部",10000);
    //創(chuàng)建兩個(gè)員工：研發(fā)部工程師
    Employee engineer1 = new Employee("左弓成","研發(fā)部",10000);
    Employee engineer2 = new Employee("成顏發(fā)","研發(fā)部",10000);
    //總裁添加下屬
    president.add(directorSales);
    president.add(directorRND);
    //銷售部部門領(lǐng)導(dǎo)添加下屬
    directorSales.add(saler1);
    directorSales.add(saler2);
    //研發(fā)部部門領(lǐng)導(dǎo)添加下屬
    directorRND.add(engineer1);
    directorRND.add(engineer2);
    //打印輸出所有員工
    System.out.println(president);
    for(Employee directorEmployee: president.getSubordinates()) {
      System.out.println(directorEmployee);
      for(Employee employee: directorEmployee.getSubordinates()) {
        System.out.println(employee);
      }
    }
  }
}