1.定义

提供一种方法顺序访问某个容器的元素，但是又不暴露容器内部的数据显示

2.示例

public interface Iterator<T> {
    T next();
    boolean hasNext();
}

/**
 *qq迭代器
 *@author woochen123
 *@time 2017/11/23 9:20
 *@desc
 */
public class QQIterator implements Iterator<UserBean> {
    List<UserBean> list;
    int index;

    public QQIterator(List<UserBean> list) {
        this.list = list;
    }

    @Override
    public UserBean next() {
        return list.get(index++);
    }

    @Override
    public boolean hasNext() {
        return index < list.size();
    }
}

/**
 *微信迭代器
 *@author woochen123
 *@time 2017/11/23 9:19
 *@desc
 */
public class WxIterator implements Iterator<UserBean> {
    UserBean[] array;
    int index;

    public WxIterator(UserBean[] array) {
        this.array = array;
    }

    @Override
    public UserBean next() {
        return array[index++];
    }

    @Override
    public boolean hasNext() {
        return index < array.length;
    }

}

public interface Aggregate<T> {
    /**
     * 公共接口
     * @return 返回迭代器
     */
    Iterator<T> interator();
}

/**
 * qq登录系统
 * @author chenwuchao
 * @time 2017/11/22 17:14
 * @desc
 */
public class QQUserSystem implements Aggregate<UserBean>{
    List<UserBean> list;

    public QQUserSystem() {
        list = new ArrayList<>();
        list.add(new UserBean("小明", "12"));
        list.add(new UserBean("小红", "13"));
        list.add(new UserBean("小刚", "14"));
    }

    public List<UserBean> elements() {
        return list;
    }

    @Override
    public Iterator<UserBean> interator() {
        return new QQIterator(list);
    }

}

/**
 *微信登录系统
 *@author woochen123
 *@time 2017/11/23 9:23
 *@desc
 */
public class WxUserSystem implements Aggregate<UserBean>{
    private UserBean[] array ;

    public WxUserSystem() {
        array = new UserBean[3];
        array[0] = new UserBean("小花","12");
        array[1] = new UserBean("小华","13");
        array[2] = new UserBean("小方","14");
    }

    public UserBean[] elements() {
        return array;
    }

    @Override
    public Iterator<UserBean> interator() {
        return new WxIterator(array);
    }
}

public class Client {
    private QQUserSystem qqUserSystem;
    private WxUserSystem wxUserSystem;

    public void main(){
        UserBean userBean = new UserBean("woochen123","123456");
        qqUserSystem = new QQUserSystem();
        wxUserSystem = new WxUserSystem();
        //qq系统中查询
        UserBean userInfo = query(userBean, qqUserSystem.interator());
        //从wx系统中查询
        if(userInfo == null){
            userInfo = query(userBean,wxUserSystem.interator());
        }
    }

    private UserBean query(UserBean userBean, Iterator<UserBean> interator) {
        while (interator.hasNext()) {
            UserBean element = interator.next();
            if (element.getName().equals(userBean.getName()) && element.getPwd().equals(userBean.getPwd())) {
                return element;
            }
        }
        return null;
    }

}