How to remove all the keys whose values are either blank, null or empty

Question

    Map<String, Object> m = new HashMap<>();
    ArrayList<String> str = new ArrayList<String>(Arrays.asList("Mohan", "Rohan", "", null));
    m.put("k1", str);
    m.put("k2", 43);
    m.put("k3", null);
    m.put("k4", "");
    System.out.println(m);
    Set<Map.Entry<String, Object>> entrySet = m.entrySet();
    Iterator<Map.Entry<String, Object>> itr = entrySet.iterator();
    while (itr.hasNext()) {
        Map.Entry<String, Object> entry = itr.next();
        if (entry.getValue() == null || entry.getValue().toString().equals("")) {
            itr.remove();
        } else if (entry.getValue().getClass() == ArrayList.class) {
            ArrayList<String> arr = (ArrayList<String>) entry.getValue();
            for (int i = 0; i < arr.size(); i++) {
                if (arr.get(i) == null || arr.get(i).trim() == "") {
                    arr.remove(i);
                }
            }
        }
    }

I am getting stuck to remove empty and null values from arraylist Can anyone help me with this...

Does this answer your question? [How do I compare strings in Java?](https://stackoverflow.com/questions/513832/how-do-i-compare-strings-in-java) — f1sh, Mar 14 '22 at 09:49
@f1sh I think OP is struggling to remove elements from list(there is error in removal logic), not with string comparison. — Chaosfire, Mar 14 '22 at 09:58
@Chaosfire OP's `arr.get(i).trim() == ""` is definitely a problem though. — f1sh, Mar 14 '22 at 10:00
@f1sh You are right, it's definitely a problem as well, somehow i totally missed it. — Chaosfire, Mar 14 '22 at 10:36
Why this inconsistency? At one place you’re only comparing with `""`, at the other place, you’re calling `trim()` before comparing. Besides that, don’t reinvent the wheel. Remove `null` and empty string from map: `m.values().removeAll(Arrays.asList(null, ""));` Remove the same from lists in the map: `m.values().forEach(o -> { if(o instanceof List) ((List>)o).removeAll( Arrays.asList(null, "")); });` — Holger, Mar 14 '22 at 19:19

score 1 · Answer 1 · answered Mar 14 '22 at 09:54

Your problem is that you remove element at index i, then the collection size changes, but you don't update index. This causes you to skip elements. To fix it you need to decrement index after removal:

arr.remove(i);
i--;

But it's not good idea to change indexes during iteration, it's error prone. It would be better to:

Make iteration backwards

for (int i = arr.size() - 1; i >= 0; i--)

Like this you don't need to change index when removing

Better would be to use Iterator.remove(), the same way you are removing elements from map
Probably easiest solution - use Collection.removeIf(Predicate)

arr.removeIf(str -> str == null || str.trim().isEmpty());

To citate java doc - Removes all of the elements of this collection that satisfy the given predicate.

@UditSingh If the answer worked/solved your problem, consider accepting it. — Chaosfire, Mar 14 '22 at 10:44

score 0 · Answer 2 · answered Mar 14 '22 at 16:37

You could interrogate the map and remember items that match your criteria in a list. Then remove those items from the map like this:

Map<String, Object> m = new HashMap<>();
m.put("k3", null);
m.put("k4", "");

List<String> keysToRemove = new ArrayList();

m.forEach((key, value) -> {
  if (value == null ) {
    keysToRemove.add(key);
  }else if(value instanceof ArrayList){
    if(((ArrayList<String>) value).stream().filter(item -> item != null || !item.isEmpty()).count() == 0){
      keysToRemove.add(key);
    }
  }
});
for (String key : keysToRemove) {
  m.remove(key);
}

Instead of `for (String key : keysToRemove) { m.remove(key); }` you can simply use `m.keySet().removeAll(keysToRemove);` — Holger, Mar 14 '22 at 19:21

How to remove all the keys whose values are either blank, null or empty

2 Answers2