10.迭代器模式

迭代器模式簡單的說就是將含有相同類型的"集合"但不同"集合"類型的兩類甚至更多類融合在一起進行遍歷 .

1.含有的相同類型(這裡以菜單為例)

public class MenuItem {
	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 this.name;
	}
	public String getDescription(){
		return this.description;
	}
	public double getPrice(){
		return this.price;
	}
	public boolean isVegetarian(){
		return this.vegetarian;
	}
}

2.將兩種不同方式,統一繼承Iterator介面

public class DinerMenuIterator implements Iterator {

	MenuItem[] items;
	int position=0;
	public DinerMenuIterator(MenuItem[] items){
		this.items=items;
	}
	public boolean hasNext() {
		if(position>=items.length || items[position]==null){
			return false;
		}
		return true;
	}

	public Object next() {
		MenuItem menuItem=items[position];
		position++;
		return menuItem;
	}

	public void remove() {
		// TODO Auto-generated method stub
		
	}

}

public class PancakeHouseIterator  implements Iterator{

	ArrayList<MenuItem> items;
	int position=0;
	public PancakeHouseIterator(ArrayList<MenuItem> items){
		this.items=items;
	}
	public boolean hasNext() {
		if(position>=items.size()){
			return false;
		}
		return true;
	}

	public Object next() {
		
		
		return items.get(position++);
	}

	public void remove() {
		// TODO Auto-generated method stub
		
	}

}

3.存儲“集合”的不同方式（其實可以統一繼承一個含有createIterator方法的介面）

1)  數組的存儲方式

public class ArrayItem {
	private MenuItem[] items;
	private int itemCount;
	public ArrayItem(int count){
		items=new MenuItem[count];
		itemCount = 0;
	}
	public void addItem(String name,String des,boolean vege,double price){
		MenuItem item=new MenuItem(name, des, vege, price);
		items[itemCount] = item;
		this.itemCount++;
	}
	public Iterator createIterator(){
		return new DinerMenuIterator(items);
	}
}

2)list的存儲方式

public class ListItem {
	private ArrayList<MenuItem> items;
	
	public ListItem(){
		items=new ArrayList();
		
	}
	public void addItem(String name,String des,boolean vege,double price){
		MenuItem item=new MenuItem(name, des, vege, price);
		items.add(item);
	}
	public Iterator createIterator(){
		return new PancakeHouseIterator(items);
	}
}

4.客戶程式

public class Waitress {
	ListItem pancakeHouseMenu;
	ArrayItem dinerMenu;
	public Waitress(ListItem pancakeHouseMenu,ArrayItem dinerMenu){
		this.pancakeHouseMenu=pancakeHouseMenu;
		this.dinerMenu=dinerMenu;
	}
	public void printMenu(){
		Iterator pancakeHouseIte=this.pancakeHouseMenu.createIterator();
		Iterator  dinerIte =this.dinerMenu.createIterator();
		printMenu(pancakeHouseIte);
		printMenu(dinerIte);
	}
	private void printMenu(Iterator iterator){
		while(iterator.hasNext()){
			MenuItem item = (MenuItem)iterator.next();
			
			System.out.println(item.getName()+":"+item.getDescription()+":"+item.getPrice());
		}
	}
}

5.應用

public class App {
	public static void main(String[] args) {
		ListItem listItem=new ListItem();
		listItem.addItem("list", "list", true, 22);
		ArrayItem arrayItem=new ArrayItem(6);
		arrayItem.addItem("array", "array", false, 33);
		Waitress waitress=new Waitress(listItem, arrayItem);
		waitress.printMenu();
	}
	
	
}