I have trouble incrementing a variable. Why?

Question

What's wrong with this? Specifically, what's wrong with intCount.put(i, intCount.get(i)++) ?

public static Map<Integer, Integer> countNumbers(List<Integer> list) {
    Map<Integer, Integer> intCount = new TreeMap<>();
    for (Integer i : list) {
      if (intCount.get(i) == null) {
        intCount.put(i, 1);
      } else {
        intCount.put(i, ++intCount.get(i));
      }
    }
    return intCount;
  }

This works, on the other hand

public static Map<Integer, Integer> countNumbers(List<Integer> list) {
    Map<Integer, Integer> intCount = new TreeMap<>();
    for (Integer i : list) {
      if (intCount.get(i) == null) {
        intCount.put(i, 1);
      } else {
        intCount.put(i, intCount.get(i) + 1);
      }
    }
    return intCount;
  }

Does it mean I can't increment Integer s, only int primitives? The problem is when I cast Integer into its respective primitive (or rather, an Integer returning method into its respective primitive) like this

intCount.put(i, ++(int)(intCount.get(i)));

it doesn't work either? Why?

Main.java:30: error: unexpected type

intCount.put(i, ++(int)(intCount.get(i)));

^ required: variable

found: value

1 error

Answer 1

intCount.get(i) gets a value, there is no variable to increment. Regardless, I would remove the if and else entirely and use Map.getOrDefault(Object, V) like

intCount.put(i, intCount.getOrDefault(i, 0) + 1);