HCLTech Java Developer Interview Questions and Answers

OOP is a programming paradigm based on objects, encapsulating data and behavior for modular and reusable code.

• Encapsulation: Bundling data and methods that operate on the data within one unit (e.g., a class).

• Inheritance: Mechanism to create a new class using properties and methods of an existing class (e.g., class Dog inherits from class Animal).

• Polymorphism: Ability to present the same interface for different und...read more

Exception handling is used to manage errors and maintain normal program flow in Java applications.

• Improves program reliability by catching runtime errors. Example: Catching a NullPointerException.

• Allows graceful degradation of functionality. Example: Providing a fallback mechanism when a service is unavailable.

• Facilitates debugging by providing stack traces. Example: Using printStackTrace() to identify the source ...read more

Inheritance is a fundamental OOP concept allowing a class to inherit properties and methods from another class.

• Promotes code reusability by allowing new classes to use existing class features.

• Supports method overriding, enabling a subclass to provide a specific implementation of a method.

• Facilitates a hierarchical classification of classes, making it easier to manage and understand code.

• Example: A 'Dog' class can ...read more

A functional interface is an interface with a single abstract method, enabling the use of lambda expressions in Java.

• A functional interface can have multiple default or static methods.

• It is annotated with @FunctionalInterface for clarity.

• Example: Runnable (void run()), Comparator (int compare(T o1, T o2)).

• Lambda expressions can be used to implement functional interfaces.

To connect 2 DBs from a Spring Boot application, configure multiple data sources and use JdbcTemplate or EntityManager for each DB.

• Configure multiple data sources in the application.properties file

• Create separate configuration classes for each data source

• Use JdbcTemplate or EntityManager to interact with each DB

• Specify the appropriate data source in the repository or service classes

HashMap is a data structure that stores key-value pairs and uses hashing to efficiently retrieve values.

• HashMap uses an array of linked lists to store key-value pairs.

• The key is hashed to determine the index in the array where the value will be stored.

• If multiple keys hash to the same index, a linked list is used to handle collisions.

• HashMap allows one null key and multiple null values.

• Example: HashMap<String, ...read more