Question

What is the difference between Hashtable and HashMap?

Options:

Hashtable is synchronized, while HashMap is not.
HashMap allows null keys and values, while Hashtable does not.
Hashtable is part of the Java Collections Framework, while HashMap is not.
HashMap is faster in most cases, while Hashtable is slower due to synchronization.

Answer 1

Hashtable and HashMap are both classes in Java that implement the Map interface and are used to store key-value pairs. Hashtable is synchronized and part of the Java Collections Framework, while HashMap is not synchronized and allows null keys and values. HashMap is faster in most cases compared to Hashtable.

Step-by-step explanation:

The Hashtable and HashMap are both classes in Java that implement the Map interface and are used to store key-value pairs. Here are the key differences between them:

1. Hashtable is synchronized, while HashMap is not: This means that Hashtable is thread-safe, allowing multiple threads to access the Hashtable concurrently without any issues. On the other hand, HashMap is not synchronized, so if multiple threads try to access it simultaneously, it may lead to data inconsistencies.
2. HashMap allows null keys and values, while Hashtable does not: HashMap allows one null key and multiple null values. However, Hashtable does not allow any null keys or values. If you try to put null in Hashtable, it will throw a NullPointerException.
3. Hashtable is part of the Java Collections Framework, while HashMap is not: Being in the Java Collections Framework, Hashtable supports enumeration and iterator methods, making it compatible with older versions of Java. HashMap, on the other hand, offers the advantage of being simpler and faster.

Overall, HashMap is preferred over Hashtable in most cases due to its better performance, but if you require thread safety or need to work with legacy code, Hashtable can be a suitable choice.