How to parse List in android?

Question

Im trying to store data like associative array in JAVA. so i took list with maps

List<Map> processNeedImages = null; 
int flag =0;
if(c.moveToFirst()){
    do{
         Map<String, String> map = null;
         map.put("status", c.getString(c.getColumnIndex("system_url")));
         processNeedImages.add(flag++, map);
      }while(c.moveToNext());

I could not parse this data

List<Map> allImages = getData();
for (Map map:allImages){
    Log.d("listImage", String.valueOf(map.get("status")));
}

Even loop is iterating even once.

what is `getData()`, is it return the same as mentioned above?? — ELITE, Feb 28 '16 at 05:54
does the first part of code works without any exception or error?? — ELITE, Feb 28 '16 at 05:57
Your list is this `processNeedImages = null;` and you are adding `processNeedImages.add(flag++, map);` like this, it must throw `java.lang.NullpointerException`.. — ELITE, Feb 28 '16 at 06:01
I debugged yes throws `java.lang.NullPointerException` sorry for previous reply. how to initialize then? — Thamaraiselvam, Feb 28 '16 at 06:03
Let us [continue this discussion in chat](http://chat.stackoverflow.com/rooms/104764/discussion-between-elite-and-thamaraiselvam). — ELITE, Feb 28 '16 at 06:07

score 1 · Answer 1 · answered Feb 28 '16 at 06:03

1

Map<String, String> map = null

should be replaced with

Map<String, String> map = new HashMap<>();

You are not creating a new map object. Rather you are adding the same map object everytime. although you are adding new values to the map for each cursor position but the object is only one. Hence your loop is going only one time.

answered Feb 28 '16 at 06:03

Ankit Aggarwal

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I'm adding that map into List in every loop iteration – Thamaraiselvam Feb 28 '16 at 06:07
but that's the same map object. unless you do new HashMap<>() no new object will be created and you will be working on the same map object – Ankit Aggarwal Feb 28 '16 at 06:08

score 1 · Accepted Answer · edited May 23 '17 at 12:23

Initialize all variable in your code like below

List<Map> processNeedImages = new ArrayList<>(); 
int flag =0;
if(c.moveToFirst()){
    do{
         Map<String, String> map = new HashMap<>();
         map.put("status", c.getString(c.getColumnIndex("system_url")));
         processNeedImages.add(flag++, map);
      }while(c.moveToNext());
}

this will work fine.

You should read this answer too what is NullPointerException

How to parse List in android?

2 Answers2