Question

Java HashMap implementation has ‘next’ member in Entry private class. Since, a new value for a key will override the old value, what’s the use of ‘next’ member in the Entry class.

static class Entry<K,V> implements Map.Entry<K,V> {
        final K key;
        V value;
        Entry<K,V> next;
        final int hash;

        /**
         * Creates new entry.
         */
        Entry(int h, K k, V v, Entry<K,V> n) {
            value = v;
            next = n;
            key = k;
            hash = h;
        }
   .....

}

Answer 1

next refers to the next entry in the same bucket.

You can have multiple entries in each bucket — a bucket contains all the entries with hash code equal to some i mod 2^n for some n, not just the entry for one particular key.