組合模式

組合模式允許你將對(duì)象組合成樹(shù)形結(jié)構(gòu)來(lái)表現(xiàn)“整體/部分”層次結(jié)構(gòu)。組合能讓客戶(hù)以一致的方式處理個(gè)別對(duì)象以及對(duì)象組合。

示例—合并兩種菜單并訪問(wèn)甜品菜單和素食菜單

有兩種餐廳菜單，分別用數(shù)組和ArrayList實(shí)現(xiàn)。現(xiàn)在需要合并兩種菜單，且合并后可以讓一個(gè)女招待的類(lèi)去訪問(wèn)，不需要重復(fù)代碼就可以同時(shí)訪問(wèn)兩種菜單。 將甜品菜單添加到午餐菜單中，做到既可以訪問(wèn)餐廳的所有的菜單也可以單獨(dú)訪問(wèn)甜品菜單和素食菜單。

UML圖表示

組合模式-遍歷樹(shù)形菜單

代碼演示

組件基類(lèi)

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(xiàng)

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(wù)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(cè)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(cè)試結(jié)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
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