10+ Junior Java Developer Interview Questions and Answers for Freshers

To cut a circular cake for 8 members equally, only 2 straight cuts are needed.

• Make the first cut through the center, dividing the cake into 2 equal halves.

• Make the second cut perpendicular to the first, creating 4 equal quarters.

• Each quarter can then be further divided into 2 equal pieces, resulting in 8 equal slices.

• This method minimizes the number of cuts while ensuring equal distribution.

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 hashmap stores key-value pairs, using a hash function to compute an index for efficient data retrieval.

• Uses a hash function to convert keys into hash codes.

• Stores entries in an array, where each index corresponds to a hash code.

• Handles collisions using techniques like chaining or open addressing.

• Example: For key 'apple', hash function might return index 3, storing value at array[3].

• Resizes the array when the load factor exceeds a threshold to maintain performance.

jdk is Java Development Kit, jre is Java Runtime Environment, thread is a unit of execution, collection is a group of objects.

• JDK is a software development kit used to develop Java applications.

• JRE is a runtime environment used to run Java applications.

• Thread is a lightweight unit of execution within a process.

• Collection is a group of objects that can be manipulated as a single unit.

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.

Inheritance in Java allows a class to inherit properties and methods from another class, promoting code reusability.

• Inheritance is a fundamental concept in OOP (Object-Oriented Programming).

• It allows a subclass to inherit fields and methods from a superclass.

• Example: class Animal { void eat() { } } class Dog extends Animal { void bark() { } }

• Java supports single inheritance (one class can inherit from one superclass).

• Use 'extends' keyword to establish inheritance.

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