10+ Java J2ee Developer Interview Questions and Answers

To call multiple APIs and fetch data sequentially, use asynchronous calls and handle responses in order.

• Use asynchronous calls to make API requests in parallel

• Handle responses in order to ensure data is fetched sequentially

• Use promises or callbacks to manage the flow of data retrieval

Operations for adding and removing elements in an ArrayList in Java

• To add an element to an ArrayList, use the add() method with the index where you want to insert the element

• To remove an element from an ArrayList, use the remove() method with the index of the element you want to remove

• Example: ArrayList<String> list = new ArrayList<>(); list.add("Apple"); list.add("Banana"); list.remove(0); // Removes Apple

Session start and end in programming refers to the beginning and termination of a user's session on a website or application.

• Session start occurs when a user logs in or visits a website, creating a unique session ID.

• Session end happens when the user logs out or closes the browser, terminating the session.

• Example: In Java servlets, HttpSession object is used to manage session start and end.

Use synchronizedList() method to synchronize an ArrayList in Java.

• Create a synchronized list using Collections.synchronizedList() method.

• Example: List<String> synchronizedList = Collections.synchronizedList(new ArrayList<>());

• Access and modify the synchronized list using synchronized blocks to ensure thread safety.

A synchronous call in JavaScript is a function call that blocks the execution of the code until it completes.

• Synchronous calls wait for the function to finish before moving on to the next line of code.

• They can cause the program to become unresponsive if the function takes a long time to complete.

• Example: Using the 'fetch' API to make a synchronous call to a server.

ConcurrentHashMap is a thread-safe version of HashMap in Java.

• ConcurrentHashMap allows multiple threads to read and write to the map concurrently without the need for external synchronization.

• It achieves this by dividing the map into segments, each of which can be locked independently for better performance.

• ConcurrentHashMap is part of the java.util.concurrent package and was introduced in Java 5.

• Example: ConcurrentHashMap<String, Integer> map = new ConcurrentHashMap<>();

OOPS concepts are the principles of Object-Oriented Programming that help in designing and implementing software systems.

• Abstraction: Hiding implementation details and showing only necessary information.

• Encapsulation: Binding data and methods together to protect data from outside interference.

• Inheritance: Creating new classes from existing ones to reuse code and add new features.

• Polymorphism: Using a single interface to represent multiple entities.

• Objects: Instances of classe...read more

Servlet lifecycle involves initialization, service, and destruction phases.

• Servlet is initialized by calling init() method

• Service method is called for each request

• Servlet is destroyed by calling destroy() method

• Container manages the lifecycle of servlet

• ServletConfig and ServletContext objects are available during initialization

Collection is a framework that provides an architecture to store and manipulate a group of objects.

• Collection is an interface in Java that extends Iterable interface.

• It is used to store a group of objects.

• Collections can be of two types: List and Set.

• List is an ordered collection that allows duplicates while Set is an unordered collection that does not allow duplicates.

• Examples of collections include ArrayList, LinkedList, HashSet, TreeSet, etc.