Why Hashmap values are getting replaced when duplicate key are used, even though it uses linked list for each bucket internally?

Question

I am revising concepts of HashMap and just wanted to check how linked list implementation of each bucket of Entry class works.

public static void main(String[] args) {
    HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
    map.put(1, 1);
    map.put(1, 2);
    map.put(1, 3);
    map.put(2, 1);
    map.put(2, 2);
    System.out.println(map.values());
}

}

Above code prints 3,2. Shouldn't it print 1, 2, 3, 1, 2.

Thanks Tom, First link perfectly explains this. Please let me know how can i delete this question. — Ashutosh, Jun 05 '19 at 21:15

score 2 · Accepted Answer · answered Jun 04 '19 at 14:43

You inserted the values 1, 2, 3 into key 1, and the values 1, 2 into key 2. Each time you insert a value into a key, you overwrite the value which previously existed at the key, assuming there were a previous value. So, your code is functionally identical to this:

HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();
map.put(1, 3);
map.put(2, 2);

That is, only the latest key-value assignments actually "stick."

Why Hashmap values are getting replaced when duplicate key are used, even though it uses linked list for each bucket internally?

1 Answers1