10+ Junior Java Developer Interview Questions and Answers for Freshers

OOPs concepts are important for code reusability, maintainability, and scalability. Constructors are special methods used to initialize objects.

• OOPs concepts help in creating modular, reusable, and maintainable code.

• Inheritance, polymorphism, encapsulation, and abstraction are the four pillars of OOPs.

• Constructors are special methods used to initialize objects with default or user-defined values.

• StringBuilder is a class used to manipulate strings efficiently.

• It is important t...read more

Aggregate functions in SQL are used to perform calculations on a set of values and return a single value.

• Common aggregate functions include COUNT, SUM, AVG, MIN, and MAX.

• COUNT returns the number of rows that match a specified condition.

• SUM calculates the sum of a column's values.

• AVG calculates the average of a column's values.

• MIN returns the minimum value in a column.

• MAX returns the maximum value in a column.

• Aggregate functions can be used with the GROUP BY clause to perform ...read more

Java Virtual Machine (JVM) is responsible for executing Java programs.

• JVM is a virtual machine that interprets compiled Java code.

• It provides a runtime environment for Java programs to run.

• JVM is platform-independent and provides memory management, security, and other features.

• Java programs are compiled into bytecode, which is then executed by the JVM.

• JVM is responsible for loading classes, verifying bytecode, and executing the program.

Servlets are still relevant for web development in Java

• Servlets provide a lightweight and efficient way to handle HTTP requests and responses

• They can be used for dynamic web content generation and server-side processing

• Servlets are extensible and can be integrated with other Java technologies like JSP and JDBC

• Alternative technologies like Spring MVC and RESTful APIs build on top of Servlets

• Removing Servlets would break backward compatibility and disrupt existing Java web appl...read more

Java is a compiled language that is first compiled into bytecode and then interpreted by the Java Virtual Machine (JVM).

• Java is first compiled into bytecode by the Java compiler.

• The bytecode is then interpreted by the Java Virtual Machine (JVM) at runtime.

• This combination of compilation and interpretation makes Java a compiled language with some interpreted features.

A constructor is a special method that is used to initialize objects in Java.

• Constructors have the same name as the class they belong to.

• They are called automatically when an object is created.

• They can take parameters to initialize the object's state.

• If a class does not have a constructor, a default constructor is provided.

• Constructors can be overloaded to provide multiple ways to initialize an object.

Spring Boot CRUD example is a basic implementation of Create, Read, Update and Delete operations using Spring Boot framework.

• Create a Spring Boot project with required dependencies

• Define entity classes and their relationships

• Create repository interfaces extending JpaRepository

• Implement service classes with business logic

• Create RESTful API endpoints using @RestController

• Use HTTP methods to perform CRUD operations

• Test the API using tools like Postman

To call REST APIs, use HTTP methods like GET, POST, PUT, DELETE with the API endpoint URL.

• Use a HTTP client library like Apache HttpClient or OkHttp

• Pass any required parameters in the request body or as query parameters

• Handle the response returned by the API

• Add appropriate headers like Authorization or Content-Type if required

JDBC Connection steps

• Load the JDBC driver class

• Establish a connection to the database using DriverManager.getConnection()

• Create a statement object using the connection.createStatement() method

• Execute the SQL query using statement.executeQuery() method

• Process the ResultSet object returned by the query

• Close the connection and statement objects using close() method

Update query to modify data in a database table

• Use UPDATE statement followed by table name

• Set the column(s) to be updated using SET keyword

• Specify the new values for the column(s) to be updated

• Add WHERE clause to specify the condition for updating specific rows