Top 5 Java collections interview questions with answers
Please share, support and subscribe.
Connect with us on:
Facebook : / onlinerostrum
Website: http://erostrum.com/
About Online Rostrum:
This is a tech channel and we are sharing knowledge and helping our community.
1. What is the difference between ArrayList and LinkedList in Java?
Answer: ArrayList and LinkedList both implement the List interface in Java, but they have different underlying data structures. ArrayList uses an array to store its elements and provides constant-time access to elements based on their index. LinkedList uses a doubly linked list to store its elements and provides constant-time insertion and deletion operations at the beginning and end of the list. Therefore, ArrayList is preferred when you need fast access to elements and LinkedList is preferred when you need fast insertion and deletion.
2. What is the difference between HashSet and TreeSet in Java?
Answer: HashSet and TreeSet both implement the Set interface in Java, but they have different underlying data structures. HashSet uses a hash table to store its elements and provides constant-time insertion, deletion, and lookup operations. TreeSet uses a red-black tree to store its elements and provides logarithmic-time operations for insertion, deletion, and lookup. Therefore, HashSet is preferred when you need fast access to elements and don't care about order, while TreeSet is preferred when you need elements to be sorted in a specific order.
3. What is the difference between HashMap and TreeMap in Java?
Answer: HashMap and TreeMap both implement the Map interface in Java, but they have different underlying data structures. HashMap uses a hash table to store its key-value pairs and provides constant-time insertion, deletion, and lookup operations. TreeMap uses a red-black tree to store its key-value pairs and provides logarithmic-time operations for insertion, deletion, and lookup. Therefore, HashMap is preferred when you need fast access to key-value pairs and don't care about order, while TreeMap is preferred when you need key-value pairs to be sorted in a specific order.
4. What is the difference between a Queue and a Stack in Java?
Answer: Both Queue and Stack are interfaces in Java that provide different ways to store and access elements. A Queue is a collection that orders its elements in a specific order for processing, such as FIFO (First In, First Out) or LIFO (Last In, First Out). A Stack is a subclass of Vector that implements LIFO (Last In, First Out) behavior. In a Queue, elements are added to the end and removed from the front, while in a Stack, elements are added to the top and removed from the top.
5. What is the difference between a Hashtable and a HashMap in Java?
Answer: Hashtable and HashMap both implement the Map interface in Java, but they have different characteristics. Hashtable is thread-safe and synchronized, which means that it can be safely accessed by multiple threads at the same time, but it can be slower than HashMap because of the synchronization overhead. HashMap is not synchronized, which means that it is not thread-safe by default, but it can be made thread-safe by wrapping it with Collections.synchronizedMap(). Hashtable does not allow null keys or values, while HashMap allows one null key and multiple null values.