添加Hashmap时的ArrayList提供NPE

Question

    subMap = new HashMap<String, String>();
    cursor = sdB.query(DataBase.TB, cols, null, null, null, null, null);
    cursor.moveToFirst();
    limit = 1;
    while(cursor.moveToNext()){
        limit +=1;
    }
    limit *= 2;
    cursor.moveToFirst();
    do{
        for(i=i+1; i<limit; i++){
            if(i%2!=0){
                subCode = cursor.getString(cursor.getColumnIndex(DataBase.C_CODE));
                subMap.put(TAG_SUB_CODE, subCode);
                Log.i("Alert", subCode);

                subjects.add(subMap);
                break;
            }
            else{
                subName = cursor.getString(cursor.getColumnIndex(DataBase.SUB_TITLE));
                subMap.put(TAG_SUB_NAME, subName);
                if(subMap.containsKey(TAG_SUB_NAME))
                    Log.i("Alert", "Yes");
                if(subMap.containsValue(subName))
                    Log.i("Alert", "Again Yes");
                Log.i("Alert", TAG_SUB_NAME);
                Log.i("Alert", subName);
                subjects.add(subMap);
            }
        }
    }while(cursor.moveToNext());

    cursor.close();

Gives me an NPE on subjects.add(subMap) in both if and else statement. First else is executed then if. But program stops at first encounter with it in else block. Can Anyone please help me. I checked the existance of value and key in hashmap and it returned me true ( yes and again yes ) in my log cat but still the subjects.add(subMap) returns an NPE.

Thank You

Answer 1

You need to initialize your list subjects . For example like this:

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

If you don't do that then at this line:

subjects.add(subMap);

an NPE will be thrown.

Answer 2

Most likely subjects is null. Have you initialized it like this:

ArrayList<Map<String, String>> subjects = new ArrayList<Map<String, String>>();