概念

迭代器模式 (Iterator) ，它可以让用户透过特定的接口巡访容器中的每一个元素而不用了解底层的实现。

举例

定义迭代器接口
interface Iterator{
    Object first();
    Object next();
    boolean hasNext();
    Object current();
}
实现接口
class ConcreteIterator implements Iterator {
    private List<Object> list = new ArrayList<Object>();
    private int curr = 0;
    public ConcreteIterator(List<Object> list) {
        this.list = list;
    }

    public Object first(){
        return list.get(0);
    }

    public Object next() {
        Object ret = null;
        curr++;
        if(curr < list.size()) {
            ret = list.get(curr);
        }
        return ret;
    }

    public boolean hasNext() {
        return curr >= list.size() ? true : false;
    }

    public Object current() {
        return list.get(curr);
    }
}
定义迭代器构造抽象类
abstract class Aggregate {
    abstract Iterator createIterator();
}
实现抽象类
class ConcreteAggregate extends Aggregate {
    private List<Object> list = new ArrayList<Object>();
    public ConcreteAggregate(List<Object> list) {
        this.list = list;
    }
    public Iterator createIterator() {
        return new ConcreteIterator(list);
    }
}
执行类：RunMain
public class RunMain {
    public static void main(String[] args) {
        List<Object> list = new ArrayList<Object>();
        list.add("我是迭代器的第一项");
        list.add("我是迭代器的第二项");
        Aggregate agg = new ConcreteAggregate(list);
        Iterator iterator = agg.createIterator();
        iterator.first();
        while(!iterator.hasNext()) {
                System.out.println(iterator.current());
                iterator.next();
            }
        }
    }
}
结果
我是迭代器的第一项
我是迭代器的第二项