What type is a HashMap bucket

Question

I've been digging into the HashMap implementation in Java. All values are stored in a 'bucket' that is an Entry object. I was expecting it to be a collection or am I missing something here?

Answer 1

Nope. Since it doesn't have to let users access the buckets through the API, HashMap gets reduced memory usage and a simpler implementation by just rolling its own very small linked list implementation internally. It could use LinkedList , but it has no need of a doubly-linked list, and it's more efficient to pack the link, the key, the value, the key's hash code, etc. into one object.

Answer 2

The Entry is a collection (a light-weight linked list of sorts. Not a java Collection strictly speaking). Entries can link each other.

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

Answer 3

我不知道您要查看的是谁的实现，但是在OpenJDK 6版本中 ，很明显，一个Entry存储一个值，并且每个Entry形成一个链表中的节点。