Unsorted entries
Unordered entries
Duplicates elements not allowed

HashMap<Integer, String> hm = new HashMap<>();

hm.clear();
// hm.put(null, "x"); // ok
// hm.put(0, null); // OK
hm.put(0, "a");
hm.put(11, "f");
hm.put(222, "e");
hm.put(3333, "d");
hm.put(44444, "c");
hm.put(555555, "b");
hm.put(6666666, "g");

for (Map.Entry<Integer, String> entry : hm.entrySet()) {
    System.out.println(entry.getKey() + " = " + entry.getValue());
}

Output:

0 = a
3333 = d
11 = f
555555 = b
44444 = c
222 = e
6666666 = g