C # Convert to Java, vector hashtable obsolete?

Vector Hashtable obsolete?

When you use the Java collection, the IDE prompts

Vectors and Hashtable are ArrayList, HashMap instead, while the former is thread-synchronized, do not know why? Is the reason for the poor efficiency?

Map
|--hashtable: The underlying is a hash table data structure that cannot be stored as a null key null value. The collection is thread-synchronized. jdk1.0. Low efficiency.
|--hashmap: The underlying is a hash table data structure that allows NULL values and NULL keys, which are not synchronized. Replace Hashtable, jdk1.2. High efficiency.
|--treemap: The bottom layer is a two-fork tree data structure. Thread is out of sync. Can be used to sort the keys in the map collection.

Legacy container classes, as well as arrays.

Classes that use Java.util.concurrent packages when multi-threading

C # Convert to Java, vector hashtable obsolete?