java 遍历

LinkedList倒序遍历

public List<Integer> getNewsFeed(int userId) {
        List<Integer> res = new ArrayList<>();

        ListIterator<Map.Entry<Integer, Integer>> iter = new ArrayList<Map.Entry<Integer, Integer>>(tuiwen.entrySet()).listIterator(tuiwen.size());
        HashSet<Integer> myFollowee = follow.get(userId);

        while(iter.hasPrevious()) {
            Map.Entry<Integer, Integer> entry = iter.previous();
            if(entry.getValue() == userId || (myFollowee != null && myFollowee.contains(entry.getValue()))) {
                res.add(entry.getKey());
                if (res.size() == 10) break;
            }


        }

        return res;
}

 

public class Traverse {

    public static void main(String[] args) {

        //循环list
        List<Integer> dataList = new ArrayList<>();
        dataList.add(1);
        dataList.add(2);
        dataList.add(4);
        dataList.add(3);
        System.out.println(dataList);

        //方式一: foreach
        for(Integer data: dataList) {
            System.out.print(data + " ");
        }
        System.out.println();

        //方式二，for 下标
        for(int i = 0; i < dataList.size(); i ++) {
            System.out.print(dataList.get(i) + " ");
        }
        System.out.println();

        //方式三：迭代器
        Iterator<Integer> listIter = dataList.iterator();
        while(listIter.hasNext()) {
            Integer data = listIter.next();
            System.out.print(data + " ");
        }
        System.out.println();


        //循环set
        HashSet<Integer> dataSet = new HashSet<>();
        dataSet.addAll(dataList);
        System.out.println(dataSet);

        //方式一：foreach
        for(Integer data: dataSet) {
            System.out.print(data + " ");
        }
        System.out.println();

        //方式二：迭代器
        Iterator<Integer> setIter = dataSet.iterator();
        while(setIter.hasNext()) {
            System.out.print(setIter.next() + " ");
        }
        System.out.println();


        //循环映射
        HashMap<Integer, Integer> dataMap = new HashMap<>();
        dataMap.put(1,1);
        dataMap.put(2,2);
        dataMap.put(3,4);

        //方法一：迭代器
        Iterator<Map.Entry<Integer, Integer>> entryIter = dataMap.entrySet().iterator();
        while(entryIter.hasNext()) {
            Map.Entry<Integer, Integer> entry = entryIter.next();
            System.out.println(entry.getKey() + " " + entry.getValue());
        }

        //方法一：倒序迭代器
        ListIterator<Map.Entry<Integer, Integer>> reEntryIter = new ArrayList<Map.Entry<Integer, Integer>>(dataMap.entrySet()).listIterator(dataMap.size());
        while(reEntryIter.hasPrevious()) {
            Map.Entry<Integer, Integer> entry = reEntryIter.previous();
            System.out.println(entry.getKey() + " " + entry.getValue());
        }

        //方法二：foreach
        for(Map.Entry<Integer, Integer> entry: dataMap.entrySet()) {
            System.out.println(entry.getKey() + " " + entry.getValue());
        }



    }
}