What is the difference between HashMap and Hashtable

HashMap and Hashtable are both data structures used in Java for storing key-value pairs. However, they have several key differences:

• Synchronization: Hashtable is synchronized, which means it is thread-safe and can be used in multi-threaded applications. HashMap, on the other hand, is not synchronized and is not thread-safe unless explicitly synchronized.
• Performance: Because Hashtable is synchronized, it tends to be slower than HashMap for non-threaded applications.
• Null values: HashMap allows one null key and multiple null values, while Hashtable does not allow any null keys or values.
• Legacy: Hashtable is considered a legacy class, whereas HashMap is part of the Java Collections Framework introduced in Java 2.