Thread Safety:
Hashmap is not thread safety,it does not provide synchronization, and it is suitable for single-thread applications.
Hashtable is thread-safe, All methods in the hashtable is synchronized, making it safe to use a multi-threaded environment without using additional synchronization.
Synchronization:
HashMap does not synchronization its method ,so its faster as compare to the hashtable.
Hashtable synchronized every method which ensures thread safety so that it's slower in nature
Null Keys and Values:
Hashmap allows only one null key and multiple null values.
Hashtable doesn't allow null or null values .
Performance:
Hashmap generally offers better perfomance than hashtable because its non synchronization in nature .
Hashtable is slower in nature as compare to hashmap because it is synchronized in nature.
Iteration Order:
Neither hashmap nor hashtable will guarantee a specific iteration order.
Legacy:
HashMap was introduced in Java 1.2 as part of the Java Collections Framework, which modernized Java’s approach to collections.
Hashtable is an older class that predates the Java Collections Framework. It has been part of Java since the early versions (before Java 2) and is considered a legacy class.
Inheritance:
HashMap extends AbstractMap<K, V>, which is a part of the Java Collections Framework and provides a skeletal implementation of the Map interface.
Hashtable extends Dictionary<K, V>, which is an abstract class that was part of the original Java collections. A dictionary is now considered obsolete.
Fail-Fast Behavior:
HashMap is fail-fast when iterating through its entries. If the map is modified after the iterator is created (except through the iterator's own methods), a ConcurrentModificationException is thrown.
Hashtable is also fail-fast in terms of iteration; however, since its methods are synchronized, the fail-fast behavior is mitigated by thread safety.
Usage Recommendation:
HashMap is recommended for general use in single-threaded environments or where manual synchronization is handled.
Hashtable may be used in legacy codebases or in cases where thread safety is required without manually managing synchronization. However, modern alternatives like ConcurrentHashMap are typically preferred for thread-safe operations.
