/**
* Hash the specified keys.
*
* @param key1 first key
* @param key2 second key
* @param key3 third key
* @param key4 fourth key
* @return hash code for the specified keys
*/
private int hash(final K1 key1, final K2 key2, final K3 key3, final K4 key4) {
int h = 0;
if (key1 != null) {
h ^= key1.hashCode();
}
if (key2 != null) {
h ^= key2.hashCode();
}
if (key3 != null) {
h ^= key3.hashCode();
}
if (key4 != null) {
h ^= key4.hashCode();
}
h += ~(h << 9);
h ^= (h >>> 14);
h += (h << 4);
h ^= (h >>> 10);
return h;
}
