Replacement for obsolete Hashtable class in Java

Question

When I tried to use the hashtable class, Netbeans gave me an error saying:

While still supported, these classes were made obsolete by the JDK1.2 colle

Answer 1

You should use HashMap, but it is not designed for concurrent environments, where you may use ConcurrentHashMap.

OR

Map<K,V> myMap = Collections.synchronizedMap(/*any map instance*/);

Answer 2

The most direct replacement of a Hashtable is a HashMap.

One difference that could be important is that all relevant methods of Hashtable are synchronized while they are not synchronized on HashMap.

Answer 3

There are cases when a method outside your control requires an Hashtable. Java's own javax.management.ObjectName is such an example^[1].

When the external interface requires it you have to use Hashtable. In netbeans, you can use:

@SupresssWarnings("UseOfObsoleteCollectionType")

to suppress the warning locally.

See

• Java: complete list of @SuppressWarnings(...) parameters (in Netbeans)?
• Suppress deprecated import warning in Java

  ---

1: I wonder why they used Hashtable and not HashMap, since ObjectName is available since 1.5 and Hashtable is obsolete since 1.2

Answer 4

You could probably use Hashmap:

Map<String, Integer> mymap = new HashMap<String, Integer>();

Answer 5

Summary

The closest replacement is HashMap (usually via the Map interface).

---

But note that Hashtable is thread-safe while HashMap is not. This is not a problem in most cases and it was intentional to make most Java collections non-thread-safe to avoid performance penalty for most common scenarios. But if you relied on Hashtable thread-safety and now need a replacement that would also be thread-safe then you have two options:

• If you need a simple synchronization wrapper for an existing Map - use Collections.synchronizedMap(...)
• If you need a class carefully and optimally designed for concurrent access - use ConcurrentHashMap (usually via the ConcurrentMap interface that extends the Map interface with additional concurrency features).

Answer 6

A better replacement for Hashtable is HashMap.

As for being obsolete, I have no reference to it, but the Javadoc states:

As of the Java 2 platform v1.2, this class was retrofitted to implement the Map interface, making it a member of the Java Collections Framework.

Hashtable is synchronized unlike HashMap.