What is the difference between an abstract class and an interface in Java? Answer: An abstract class can have both implemented and abstract methods, while an interface can only have abstract methods. Also, a class can implement multiple interfaces, but it can extend only one abstract class. Question: Explain the concept of polymorphism. Answer: Polymorphism allows objects of different classes to be treated as objects of a common superclass. It enables code to work with objects in a generic way without knowing their specific types, promoting flexibility and reusability. Question: What is the purpose of an index in a database? Answer: An index in a database improves query performance by creating a data structure that allows the database to quickly locate rows based on the values in specific columns. It speeds up data retrieval operations but comes at the cost of increased storage and maintenance overhead. Question: Describe the difference between stack and queue data structures. Answer: A stack is a Last-In-First-Out (LIFO) data structure, where the last element added is the first one to be removed. A queue is a First-In-First-Out (FIFO) data structure, where the first element added is the first one to be removed. Question: What is the time complexity of searching for an element in a balanced binary search tree? Answer: The time complexity of searching in a balanced binary search tree is O(log n), where n is the number of nodes in the tree. This efficiency is due to the logarithmic height of a balanced tree. Question: Explain the difference between HTTP and HTTPS. Answer: HTTP (Hypertext Transfer Protocol) is an unsecured protocol for transmitting data over the internet, while HTTPS (Hypertext Transfer Protocol Secure) encrypts the data using SSL/TLS, providing a secure and encrypted channel for data transmission. Remember, technical interviews often delve deep into your understanding of concepts, problem-solving skills, and ability to explain complex ideas clearly. Practice is key, so make sure to review and understand the underlying concepts behind these questions.