android arraylist获取哈希图位置

Question

I have an ArrayList HashMap like the one below.

    ArrayList<HashMap<String, String>> mArrType = new ArrayList<>();

with the following values added into it

    HashMap<String, String> map;

    map = new HashMap<String, String>();
    map.put("type", "TRIMMER");
    map.put("request", "5");
    map.put("actual", "0");
    mArrType.add(map);

    map = new HashMap<String, String>();
    map.put("type", "HAND ROUTER");
    map.put("request", "6");
    map.put("actual", "0");
    mArrType.add(map);

    map = new HashMap<String, String>();
    map.put("type", "AIR COMPRESSOR");
    map.put("request", "6");
    map.put("actual", "0");
    mArrType.add(map);

Question is how can i get the position of a hashmap from arraylist. eg : hashmap with 'type' trimmer has a position 0 in arraylist, I want to retrieve the position value "0"

Answer 1

I'll write a small util method

private static int getTrimmerTypeMapPosition(ArrayList<HashMap<String, String>> mArrType) {
        for (int i = 0; i < mArrType.size(); i++) {
            HashMap<String, String> mp = mArrType.get(i);
            if (mp.get("type").equals("TRIMMER")) {
                return i;
            }    
        }    
        return -1;    
    }

To make this method very generic, have "type" and "TRIMMER" as method params, so that you can just pass any key and value pairs to check with.

Answer 2

That's not efficiently possible with your data structure. You can either store the own position in each HashMap or loop through all entries and search for the one with the type you are looking for.

You can, of course, define another HashMap<String, Integer> which maps all your type strings to the corresponding ArrayList index.

Answer 3

Others answer is also correct, but you can do this thing using Java8 also.

Eg:

int index = IntStream.range(0, mArrType.size()).
                filter(i -> mArrType.get(i).get("type").equals("TRIMMER"))
                .findFirst().getAsInt();