組合模式允許你將對象組合成樹形結構來表現(xiàn)“整體/部分”層次結構渡处。組合能讓客戶以一致的方式處理個別對象以及對象組合蚀浆。
示例—合并兩種菜單并訪問甜品菜單和素食菜單
有兩種餐廳菜單罗岖，分別用數(shù)組和ArrayList實現(xiàn)。現(xiàn)在需要合并兩種菜單膳凝，且合并后可以讓一個女招待的類去訪問控妻，不需要重復代碼就可以同時訪問兩種菜單。 將甜品菜單添加到午餐菜單中看尼，做到既可以訪問餐廳的所有的菜單也可以單獨訪問甜品菜單和素食菜單递鹉。
UML圖表示
組合模式-遍歷樹形菜單
代碼演示
組件基類
package TreeMenu;
import java.util.Iterator;
public abstract class MenuComponent {
public void add(MenuComponent menuComponent){
throw new UnsupportedOperationException();
}
public void remove(MenuComponent menuComponent){
throw new UnsupportedOperationException();
}
public MenuComponent getChild(int i){
throw new UnsupportedOperationException();
}
public String getName(){
throw new UnsupportedOperationException();
}
public String getDescription(){
throw new UnsupportedOperationException();
}
public double getPrice(){
throw new UnsupportedOperationException();
}
public boolean isVegetarian(){
throw new UnsupportedOperationException();
}
public void print(){
throw new UnsupportedOperationException();
}
public Iterator createIterator(){
throw new UnsupportedOperationException();
}
}
葉子菜單項
package TreeMenu;
import java.util.Iterator;
public class MenuItem extends MenuComponent {
String name;
String description;
boolean vegetarian;
double price;
public MenuItem(String name, String description, boolean vegetarian, double price){
this.name = name;
this.description = description;
this.vegetarian = vegetarian;
this.price = price;
}
@Override
public String toString() {
return name + ", " + price + " -- " + description;
}
@Override
public String getName() {
return name;
}
@Override
public String getDescription() {
return description;
}
@Override
public boolean isVegetarian() {
return vegetarian;
}
@Override
public double getPrice() {
return price;
}
@Override
public void print() {
System.out.print(" " + getName());
if (isVegetarian()){
System.out.print("(v)");
}
System.out.println(", " + getPrice());
System.out.println(" --" + getDescription());
}
@Override
public Iterator createIterator() {
return new NullIterator();
}
}
菜單
package TreeMenu;
import java.util.ArrayList;
import java.util.Iterator;
public class Menu extends MenuComponent {
ArrayList menuComponents = new ArrayList();
String name;
String description;
public Menu(String name, String description){
this.name = name;
this.description = description;
}
@Override
public void add(MenuComponent menuComponent){
menuComponents.add(menuComponent);
}
@Override
public void remove(MenuComponent menuComponent){
menuComponents.remove(menuComponent);
}
@Override
public MenuComponent getChild(int i) {
return (MenuComponent)menuComponents.get(i);
}
@Override
public String getName() {
return name;
}
@Override
public String getDescription() {
return description;
}
@Override
public void print() {
System.out.print("\n" + getName());
System.out.println("," + getDescription());
System.out.println("-------------------------");
Iterator<MenuComponent> iterator = menuComponents.iterator();
while (iterator.hasNext()){
MenuComponent menuComponent = iterator.next();
menuComponent.print();
}
}
@Override
public Iterator createIterator() {
return new CompositeIterator(menuComponents.iterator());
}
}
組合迭代器
package TreeMenu;
import java.util.Iterator;
import java.util.Stack;
public class CompositeIterator implements Iterator {
Stack stack = new Stack();
public CompositeIterator(Iterator iterator){
stack.push(iterator);
}
@Override
public boolean hasNext() {
if (stack.empty()){
return false;
}
else {
Iterator iterator = (Iterator) stack.peek();
if (!iterator.hasNext()) {
stack.pop();
return hasNext();
}
else{
return true;
}
}
}
@Override
public Object next() {
if (hasNext()){
Iterator iterator = (Iterator) stack.peek();
MenuComponent component = (MenuComponent) iterator.next();
if (component instanceof Menu){
stack.push(component.createIterator());
}
return component;
}
else{
return null;
}
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
空迭代器
package TreeMenu;
import java.util.Iterator;
public class NullIterator implements Iterator {
@Override
public boolean hasNext() {
return false;
}
@Override
public Object next() {
return null;
}
@Override
public void remove() {
throw new UnsupportedOperationException();
}
}
服務員
package TreeMenu;
import java.util.Iterator;
public class Waitress {
MenuComponent allMenus;
public Waitress(MenuComponent allMenus){
this.allMenus = allMenus;
}
public void printMenu(){
allMenus.print();
}
public void printVegetarianMenu(){
Iterator iterator = allMenus.createIterator();
System.out.println("\nVEGETARIAN MENU\n-----");
while (iterator.hasNext()){
MenuComponent menuComponent = (MenuComponent) iterator.next();
try {
if(menuComponent.isVegetarian()){
menuComponent.print();
}
}
catch (UnsupportedOperationException e) {}
}
}
}
測試代碼
package TreeMenu;
public class MenuTestDrive {
public static void main(String[] args) {
MenuComponent pancakeHouseMenu = new Menu("PANCAKE HOUSE MENU", "Breakfast");
MenuComponent dinerMenu = new Menu("DINER MENU", "Lunch");
MenuComponent dessertMenu = new Menu("DESSERT MENU" , "Dessert of course!");
MenuComponent allMenus = new Menu("All MENUS", "All menus combined");
allMenus.add(pancakeHouseMenu);
allMenus.add(dinerMenu);
MenuItem d1 = new MenuItem("Vegetarian BLT",
"(Fakin')Bacon with lettuce & tomato on whole wheat", true, 2.99);
MenuItem d2 = new MenuItem("Vegetarian BLT",
"(Fakin')Bacon with lettuce & tomato on whole wheat", true, 2.99);
MenuItem d3 = new MenuItem("BLT","Bacon with lettuce & tomato on whole wheat", false,2.99);
MenuItem d4 = new MenuItem("Soup of the day"
,"Soup of the day, with a side of potato salad", false,3.29);
MenuItem d5 = new MenuItem("Hotdog","A hot dog, with saurkraut, relish, onions, topped with cheese",
false,3.05);
dinerMenu.add(d1);
dinerMenu.add(d2);
dinerMenu.add(d3);
dinerMenu.add(d4);
dinerMenu.add(d5);
MenuItem p1 = new MenuItem("K&B's Pancake Breakfast",
"Pancakes with scrambled eggs, and toast",
true,2.99);
MenuItem p2 = new MenuItem("Regular Pancake Breakfast",
"Pancakes with fired eggs, sausage",
false,2.99);
MenuItem p3 = new MenuItem("Blueberry Pancakes",
"Pancakes made with fresh blueberries",
true,3.49);
MenuItem p4 = new MenuItem("Waffles",
"Waffles, with your choice of blueberries or strawberries",
true,3.59);
pancakeHouseMenu.add(p1);
pancakeHouseMenu.add(p2);
pancakeHouseMenu.add(p3);
pancakeHouseMenu.add(p4);
MenuItem ds1 = new MenuItem("Apple Pie",
"Apple Pie with a flaky crust",
true,1.59);
MenuItem ds2 = new MenuItem("Banner Pie",
"Banner Pie topped with vanilla ice cream",
true,1.59);
dessertMenu.add(ds1);
dessertMenu.add(ds2);
dinerMenu.add(dessertMenu);
Waitress waitress = new Waitress(allMenus);
waitress.printMenu();
waitress.printVegetarianMenu();
}
}
測試結果
All MENUS,All menus combined
-------------------------
PANCAKE HOUSE MENU,Breakfast
-------------------------
K&B's Pancake Breakfast(v), 2.99
--Pancakes with scrambled eggs, and toast
Regular Pancake Breakfast, 2.99
--Pancakes with fired eggs, sausage
Blueberry Pancakes(v), 3.49
--Pancakes made with fresh blueberries
Waffles(v), 3.59
--Waffles, with your choice of blueberries or strawberries
DINER MENU,Lunch
-------------------------
Vegetarian BLT(v), 2.99
--(Fakin')Bacon with lettuce & tomato on whole wheat
Vegetarian BLT(v), 2.99
--(Fakin')Bacon with lettuce & tomato on whole wheat
BLT, 2.99
--Bacon with lettuce & tomato on whole wheat
Soup of the day, 3.29
--Soup of the day, with a side of potato salad
Hotdog, 3.05
--A hot dog, with saurkraut, relish, onions, topped with cheese
DESSERT MENU,Dessert of course!
-------------------------
Apple Pie(v), 1.59
--Apple Pie with a flaky crust
Banner Pie(v), 1.59
--Banner Pie topped with vanilla ice cream
VEGETARIAN MENU
-----
K&B's Pancake Breakfast(v), 2.99
--Pancakes with scrambled eggs, and toast
Blueberry Pancakes(v), 3.49
--Pancakes made with fresh blueberries
Waffles(v), 3.59
--Waffles, with your choice of blueberries or strawberries
Vegetarian BLT(v), 2.99
--(Fakin')Bacon with lettuce & tomato on whole wheat
Vegetarian BLT(v), 2.99
--(Fakin')Bacon with lettuce & tomato on whole wheat
Apple Pie(v), 1.59
--Apple Pie with a flaky crust
Banner Pie(v), 1.59
--Banner Pie topped with vanilla ice cream
Apple Pie(v), 1.59
--Apple Pie with a flaky crust
Banner Pie(v), 1.59
--Banner Pie topped with vanilla ice cream
