Question

I read in a book where it was mentioned that when we put elements in HashMap, internally it is stored in bucket. My question is

1. Does hashmap store key-value pair altogether in the form of linked list? or does it store in linked list only when there is a collision?

2. How does it retrieve the object when 2 different objects are stored in the same bucket?

Thanks!

Answer 1

Lots of details at http://en.wikipedia.org/wiki/Hash_table

See also Internal implementation of java.util.HashMap and HashSet

And of course you can use the source, Luke.

Updated: to specifically answer your Q, it stores an Entry, which has a reference to the next item in the bucket (if any). If there is only one item in the bucket then the reference will be null:

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