Difference Between HashMap and HashTable (Interview)

The video tutorial explains the differences between hashmap and hashtable, focusing on synchronization, thread safety, handling of null values, and iteration methods. Hashmap is not synchronized and allows multiple threads to access it simultaneously, while hashtable is thread-safe, allowing only one thread at a time. Hashmap permits null keys and values, unlike hashtable. Iteration in hashmap uses the iterator interface, whereas hashtable requires the enumerator interface. These differences are crucial for understanding their use cases and are common interview questions.

What is a common interview question regarding HashMap and HashTable?

• What is the difference between HashMap and HashTable?

• What are the uses of HashMap?

• How to optimize a HashTable?

• How to implement a HashMap?

Which of the following is true about HashMap?

• It is synchronized and thread-safe.

• It does not allow null keys.

• It requires an Enumerator for iteration.

• It is not synchronized and not thread-safe.

What happens when multiple threads access a HashMap simultaneously?

• The HashMap throws an exception.

• The HashMap becomes synchronized.

• The HashMap locks until one thread finishes.

• The HashMap updates concurrently without synchronization.

Which data structure allows null keys and values?

• HashMap

• HashTable

• Neither HashMap nor HashTable

• Both HashMap and HashTable

Why might you choose a HashTable over a HashMap?

• To ensure thread safety.

• To allow null keys and values.

• To improve performance with multiple threads.

• To use an Iterator for iteration.

Which interface is used to iterate over a HashMap?

• Collection

• ListIterator

• Enumerator

• Iterator

What is required to iterate over a HashTable?

• Iterator

• Enumerator

• Collection

• ListIterator