What is alternative hashing for String keys in Java 8?

Question

Java 8 is providing alternative hashing for String keys to improve performance when a large number of key hash code collisions are encountered. Can anybody explain what is that and how it will work?

Answer 1

To bring more relevance to this question, the alternative hashing has been removed from JDK 8. Check out :

http://docs.oracle.com/javase/8/docs/technotes/guides/collections/changes8.html

http://openjdk.java.net/jeps/180

It is interesting to note that once the number of items in a hash bucket grows beyond a certain threshold, that bucket will switch from using a linked list of entries to a balanced tree.

The hash(Object key) function in the HashMap has been revised to follows with no special treatment to String objects:

static final int hash(Object key) {
    int h;
    return (key == null) ? 0 : (h = key.hashCode()) ^ (h >>> 16);
}