Why is this loop prematurely exiting when removing JSON objects?

NonCreature0714 :

I have a simple JSON array.

{
  "food" : [
    {
      "name" : "apple"
    },
    {
      "name" : "orange"
    },
    {
      "name" : "peach"
    },
    {
      "name" : "carrot"
    },
    {
      "name" : "lettuce"
    }
  ]
}

But when I try to remove all but keep one, the removal for-loop pre-emptively exits.

String itemToKeepsName = "carrot";
JSONArray list = wrappedFood.getJSONArray("food");
JSONObject addThisItemBack = null; // be ready to make a new space in memory.

println("number of items in list: " + list.length()); // prints 5.
int found = -1;
for(int i = 0; i < list.length(); ++i) {
  if(addThisItemBack.equals(list.getJSONObject(i).getString("name"))) {
    found = i;
    addThisItemBack = new JSONObject(list.getJSONObject(i).toString());
  }
}

if (found >= 0) { // found at index 3.
  println("number of items before removeall loop: " + list.length()); // prints 5.
  for (int i = 0; i < list.length(); ++i) {
    println("removed item: " + i); // prints 0, 1, 2. 
        list.remove(i);
  }

  println("adding item: " + addThisItemBack); // {"food":["name":"carrot"}]}
  list.put(addThisItemBack);

}

But this results in:

{
  "food" : [
    {
      "name" : "carrot"
    },
    {
      "name" : "lettuce"
    }
  ]
}

Instead of:

{
  "food" : [
    {
      "name" : "carrot"
    }
  ]
}

How can I make sure the list is completely emptied before I add an item back? Did I overlook something obvious? Is this something esoteric to JSON manipulation?

Elliott Frisch :

Every time you remove an element, the list shrinks. This

for (int i = 0; i < list.length(); ++i) {
    println("removed item: " + i); // prints 0, 1, 2. 
    list.remove(i);
}

Means i quickly passes the length of the list. I would suggest List.clear() like

list.clear();

or an Iterator with remove()

Iterator<JsonValue.ValueType> iter = list.iterator();
while (iter.hasNext()) {
    JsonValue.ValueType value = iter.next();
    println("removed: " + value);
    iter.remove();
}

Be aware of the note from the linked Javadoc: The behavior of an iterator is unspecified if the underlying collection is modified while the iteration is in progress in any way other than by calling this method.

Why is this loop prematurely exiting when removing JSON objects?

Guess you like