定義:組合模式將對象組合成樹形結構以表示“部分—整體”的層次關系,這使得使用者處理單個對象和組合對象時具有一致性
使用場景:當單個對象和組合對象需要對外提供類似的接口時
類圖:
代碼樣例:
package headfirst.composite.menu; import java.util.Iterator; import java.util.ArrayList; 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; } public void add(MenuComponent menuComponent) { menuComponents.add(menuComponent); } public void remove(MenuComponent menuComponent) { menuComponents.remove(menuComponent); } public MenuComponent getChild(int i) { return (MenuComponent)menuComponents.get(i); } public String getName() { return name; } public String getDescription() { return description; } public void print() { System.out.print("\n" + getName()); System.out.println(", " + getDescription()); System.out.println("---------------------"); Iterator iterator = menuComponents.iterator(); while (iterator.hasNext()) { MenuComponent menuComponent = (MenuComponent)iterator.next(); menuComponent.print(); } } }
package headfirst.composite.menu; import java.util.*; 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(); } }
package headfirst.composite.menu; import java.util.Iterator; import java.util.ArrayList; 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; } public String getName() { return name; } public String getDescription() { return description; } public double getPrice() { return price; } public boolean isVegetarian() { return vegetarian; } public void print() { System.out.print(" " + getName()); if (isVegetarian()) { System.out.print("(v)"); } System.out.println(", " + getPrice()); System.out.println(" -- " + getDescription()); } }
package headfirst.composite.menu; import java.util.Iterator; public class Waitress { MenuComponent allMenus; public Waitress(MenuComponent allMenus) { this.allMenus = allMenus; } public void printMenu() { allMenus.print(); } }
優點:1)簡化對外的使用方式
缺點:1)
類似的設計模式:
配套的內功心法:1)