1. Synchronization or Thread Safe: Hashtable is thread-safe and can be shared with many threads. On the other hand, HashMap is not thread safe. If you need to achieve thread-safety with HashMap, you must explicitly synchronize it.

2. Null keys and null values: Hashtable doesn't allow null keys or values. HashMap allows one null key and any number of null values.

3. Iterating the values: Iterator in the HashMap is fail-fast while the enumerator for the Hashtable isn't. This means when one thread changes the map structurally by adding or removing any element except Iterator's own remove() method, the Iterator fails quickly and throws ConcurrentModificationException.

4. Performance: HashMap is generally faster and uses less memory than Hashtable as it is unsynchronized.

5. Superclass and Legacy: Hashtable is a legacy class. HashMap is part of the newer Collections Framework.

6. Method Names: Some method names are different in Hashtable and HashMap like contains() in Hashtable and containsValue() in HashMap, etc.

Question

1. Synchronization or Thread Safe: Hashtable is thread-safe and can be shared with many threads. On the other hand, HashMap is not thread safe. If you need to achieve thread-safety with HashMap, you must explicitly synchronize it.

2. Null keys and null values: Hashtable doesn't allow null keys or values. HashMap allows one null key and any number of null values.

3. Iterating the values: Iterator in the HashMap is fail-fast while the enumerator for the Hashtable isn't. This means when one thread changes the map structurally by adding or removing any element except Iterator's own remove() method, the Iterator fails quickly and throws ConcurrentModificationException.

4. Performance: HashMap is generally faster and uses less memory than Hashtable as it is unsynchronized.

5. Superclass and Legacy: Hashtable is a legacy class. HashMap is part of the newer Collections Framework.

6. Method Names: Some method names are different in Hashtable and HashMap like contains() in Hashtable and containsValue() in HashMap, etc.

Knowee AI · Accepted Answer

1. Synchronization or Thread Safe: Hashtable is thread-safe and can be shared with many threads. On the other hand, HashMap is not thread safe. If you need to achieve thread-safety with HashMap, you must explicitly synchronize it.

2. Null keys and null values: Hashtable doesn't allow null keys or values. HashMap allows one null key and any number of null values.

3. Iterating the values: Iterator in the HashMap is fail-fast while the enumerator for the Hashtable isn't. This means when one thread changes the map structurally by adding or removing any element except Iterator's own remove() method, the Iterator fails quickly and throws ConcurrentModificationException.

4. Performance: HashMap is generally faster and uses less memory than Hashtable as it is unsynchronized.

5. Superclass and Legacy: Hashtable is a legacy class. HashMap is part of the newer Collections Framework.

6. Method Names: Some method names are different in Hashtable and HashMap like contains() in Hashtable and containsValue() in HashMap, etc.

What differences exist between HashMap and Hashtable?

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