迭代器模式（Iterator）要解决的问题：聚类的遍历和处理
迭代器模式（Iterator）定义：
例子：菜单合并，第一个菜单采用数组，第二个菜单采用List，第三个菜单采用（key,value），现在服务员需要打印所有菜单上的菜品
解决：让这三个菜单提供一个接口对象（该接口提供访问菜单上的菜品的方法），使用该对象即可访问菜品
数组需要实现Iterator接口，List已经实现，map.values().iterator()
参考例子-极客学院
目录结构：
Paste_Image.png
FirstMenu:
public class FirstMenu {
private MenuItem[] menu = new MenuItem[3];
private int i = 0;
public FirstMenu() {
this.addMenuItem(new MenuItem("西瓜", "我是西瓜", 1));
this.addMenuItem(new MenuItem("哈密瓜", "我是哈密西瓜", 2));
this.addMenuItem(new MenuItem("角瓜", "我是角瓜", 3));
}
public MenuItem[] getMenu() {
return menu;
}
public void addMenuItem(MenuItem item) {
menu[i] = item;
i++;
}
public Iterator getIterator() {
return new FistMenuIterator();
}
class FistMenuIterator implements Iterator {
private int position = 0;
@Override
public boolean hasNext() {
return position < FirstMenu.this.i;
}
@Override
public Object next() {
MenuItem item = FirstMenu.this.menu[this.position];
this.position++;
return item;
}
@Override
public void remove() {
}
}
}
SecondMenu:
public class SecionMenu {
private ArrayList<MenuItem> list = new ArrayList<MenuItem>();
public SecionMenu() {
this.list.add(new MenuItem("土豆", "tudobu", 4));
this.list.add(new MenuItem("茄子", "213124", 5));
this.list.add(new MenuItem("豆角", "jhgkuyi", 6));
}
public Iterator getIterator() {
return this.list.iterator();
}
}
ThirdMenu:
public class ThirdMenu {
private Map<String, MenuItem> map = new HashMap<String, MenuItem>();
public ThirdMenu() {
map.put("1", new MenuItem("牛肉", "牛肉馅饺子", 20));
map.put("2", new MenuItem("羊肉", "羊肉馅饺子", 30));
map.put("3", new MenuItem("猪肉", "猪肉馅饺子", 10));
}
public Iterator getIterator() {
return this.map.values().iterator();
}
}
菜品实体：MenuItem
public class MenuItem {
private String name;
private String desc;
private int price;
public MenuItem(String name, String desc, int price) {
this.name = name;
this.desc = desc;
this.price = price;
}
public String getName() {
return name;
}
public String getDesc() {
return desc;
}
public int getPrice() {
return price;
}
}
服务员Waitress持有访问菜单聚合实体中每个对象的接口(Iterator)的集合
public class Waitress {
private List<Iterator> list;
public Waitress() {
this.list = new ArrayList<Iterator>();
}
public void addMenu(Iterator menu) {
this.list.add(menu);
}
public void printAllMenu() {
for (Iterator iterator : list) {
System.out.println("-----------------------------");
while (iterator.hasNext()) {
MenuItem item = (MenuItem) iterator.next();
System.out.println(item.getName() + ":" + item.getDesc() + ":" + item.getPrice());
}
System.out.println("-----------------------------");
}
}
}
测试类Main：
public class Main {
public static void main(String[] args) {
FirstMenu firstMenu = new FirstMenu();
SecionMenu secionMenu = new SecionMenu();
ThirdMenu thirdMenu = new ThirdMenu();
Waitress waitress = new Waitress();
waitress.addMenu(firstMenu.getIterator());
waitress.addMenu(secionMenu.getIterator());
waitress.addMenu(thirdMenu.getIterator());
waitress.printAllMenu();
}
}
输出结果：
Paste_Image.png
总结：** 面向接口编程，接口中提供访问对象的方法（对对象的一系列动作），想对对象做某些更改或者查询时直接向外暴露接口即可。 **
