Excelon Solutions Interview Questions and Answers

Constructor is a special method used to initialize an object, while a method is a function associated with an object to perform a specific task.

• Constructor is called automatically when an object is created, while a method is called explicitly by the programmer.

• Constructors have the same name as the class, while methods have unique names.

• Constructors do not have a return type, while methods can have a return type.

• Exampl...read more

final is a keyword used to declare constants, finalize is a method used for cleanup operations, and finally is a block used for exception handling.

• final is used to declare constants in Java

• finalize is a method in Java used for cleanup operations before an object is garbage collected

• finally is a block used in exception handling to ensure a piece of code is always executed

Different types of injections in Spring Boot include constructor injection, setter injection, and field injection.

• Constructor injection: Dependencies are provided through a class constructor.

• Setter injection: Dependencies are set through setter methods.

• Field injection: Dependencies are injected directly into class fields.

Spring is a framework for building Java applications, while Spring Boot is an extension that simplifies the setup and development process.

• Spring is a comprehensive framework that provides support for various Java technologies like JDBC, JPA, and REST.

• Spring Boot is an opinionated extension of Spring that aims to simplify the setup and development of Spring applications by providing defaults for configuration.

• Spring Boo...read more

Use Spring Data JPA to connect a database to a Spring Boot application.

• Add the necessary dependencies in the pom.xml file for Spring Data JPA and the database driver.

• Configure the database connection properties in the application.properties file.

• Create a repository interface that extends JpaRepository to interact with the database.

• Use annotations such as @Entity, @Table, @Id, @Column, etc., to map Java objects to datab...read more

Access keywords control the visibility and accessibility of methods in a class.

• public: accessible from any class

• private: only accessible within the same class

• protected: accessible within the same class and its subclasses

• default (no keyword): accessible within the same package

Static methods belong to the class itself, while non-static methods belong to instances of the class.

• Static methods can be called without creating an instance of the class.

• Non-static methods require an instance of the class to be created before they can be called.

• Static methods cannot access instance variables, while non-static methods can.

• Example: Math.sqrt() is a static method, while String.length() is a non-static m

Java does not support multiple inheritance to avoid the diamond problem and maintain simplicity and clarity in the language.

• Java supports single inheritance to prevent the diamond problem, where conflicts arise when a class inherits from two classes that have a common ancestor.

• Multiple inheritance can lead to ambiguity and complexity in the code, making it harder to understand and maintain.

• Java allows multiple interfac...read more

Code to add employee table in db using Spring Boot app and retrieve data of employee with second highest salary

• Create Employee entity class with fields like id, name, salary

• Create EmployeeRepository interface extending JpaRepository

• Implement service class with methods to add employee to db and retrieve employee with second highest salary

• Use @Query annotation in repository to write custom query to retrie

Join Dept table with emp table on dept id to get department of employees

• Use SQL JOIN to connect Dept and emp tables on dept id

• Select the Dept column from Dept table to get the department of employees