Question

What happens to the HashMap after this code execution?

HashMap m  = new HashMap();
for (int i = 0; i < 1024 * 1024; i++)
    m.put(i, i);
m.clear();

After 1M puts the inner hash table will grow from original 16 to 1MB. Does clear() resize it to the original size or not?

Answer 1

No. The table retains its size. All elements are set to null:

public void clear() {
    modCount++;
    Entry[] tab = table;
    for (int i = 0; i < tab.length; i++)
        tab[i] = null;
    size = 0;
}