HeadFirst 组合模式+迭代器错误原因以及解决代码

package compositeIter; import java.util.ArrayList; import java.util.Iterator; public class Menu extends MenuComponent{ ArrayList<MenuComponent> menuComponents = new ArrayList<MenuComponent>(); String name; String description; public ArrayList<MenuComponent> getMenuComponents() { return menuComponents; } public Menu(String name,String description) { this.name = name; this.description = description; } public void add(MenuComponent menuComponent) { menuComponents.add(menuComponent); //deep++; } 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(getName()); System.out.println("--------------begin"); Iterator<MenuComponent> iterator = menuComponents.iterator(); while(iterator.hasNext()) { MenuComponent menuComponent = (MenuComponent)iterator.next(); menuComponent.print(); } System.out.print(getName()); System.out.println("---------------end"); } public Iterator createIterator() { return new CompositeIterator(menuComponents.iterator()); } }