20+ Java Developer Intern Interview Questions and Answers for Freshers

Java is a popular programming language known for its platform independence and object-oriented approach.

• Java is platform independent because it uses the concept of bytecode and virtual machine (JVM).

• Bytecode is a platform-neutral code that can be executed on any operating system or architecture.

• JVM interprets the bytecode and translates it into machine-specific instructions.

• Java is not a pure object-oriented language because it supports primitive data types like int, float, e...read more

A circular linked list is a linked list where the last node points back to the first node, forming a loop.

• Create a Node class with data and next pointer

• Initialize the head and tail pointers to null

• When adding a node, if the list is empty, set head and tail to the new node

• If the list is not empty, set the next pointer of the tail to the new node and update the tail

• To traverse the circular linked list, start from the head and keep moving to the next node until you reach the hea...read more

JIT compiler compiles bytecode to machine code at runtime. String is immutable to ensure security and thread safety. Interface defines only method signatures while abstract class can have method implementations. Process is an instance of a program while thread is a subset of a process.

• JIT compiler stands for Just-In-Time compiler and is used to improve the performance of Java programs by compiling bytecode to machine code at runtime.

• String is immutable to ensure security and ...read more

To create a singleton class in a multi-threaded environment, we can use double-checked locking or synchronized block.

• Use double-checked locking to minimize the use of synchronization and improve performance.

• In double-checked locking, check if the instance is null, then synchronize the block and create the instance.

• Use volatile keyword to ensure visibility of the instance across threads.

• Alternatively, use synchronized block to create a thread-safe singleton class.

• In synchroniz...read more

An immutable class in Java is a class whose state cannot be modified after it is created.

• Declare the class as final to prevent inheritance

• Declare all fields as private and final

• Do not provide any setter methods

• Ensure that any mutable objects within the class are not accessible or modifiable

• Provide only getter methods to access the fields

• If a field is mutable, return a copy of it instead of the original object

RDBMS is a relational database management system that uses structured data, while NoSQL is a non-relational database that uses unstructured data.

• RDBMS stores data in tables with predefined schemas, while NoSQL stores data in various formats like key-value, document, columnar, or graph.

• RDBMS supports ACID (Atomicity, Consistency, Isolation, Durability) properties, while NoSQL sacrifices some of these properties for scalability and performance.

• RDBMS is suitable for structured d...read more

No, generics are not limited to collections.

• Generics can be used with any type of class or interface, not just collections.

• They provide type safety and allow for code reusability.

• For example, generics can be used with classes like ArrayList, LinkedList, HashMap, etc.

• They can also be used with interfaces like Comparable, Iterator, etc.

HashMap is an unordered collection while LinkedHashMap maintains insertion order.

• HashMap uses hash table to store key-value pairs.

• LinkedHashMap uses doubly-linked list to maintain the insertion order.

• HashMap provides faster access and retrieval time complexity.

• LinkedHashMap provides predictable iteration order based on insertion order.

• Example: HashMap - {1=A, 2=B, 3=C}, LinkedHashMap - {1=A, 2=B, 3=C}

Java is a high-level, object-oriented programming language used for developing applications and software.

• Developed by James Gosling at Sun Microsystems in 1995

• Runs on a variety of platforms, including Windows, Mac OS, and Linux

• Used for developing web, mobile, and desktop applications

• Known for its security, reliability, and portability

• Popular frameworks include Spring, Hibernate, and Struts

Key concepts of OOP include encapsulation, inheritance, polymorphism, and abstraction.

• Encapsulation: Bundling data and methods that operate on the data into a single unit (class). Example: class Car { private String model; public void drive() { ... } }

• Inheritance: Creating new classes based on existing classes, inheriting their attributes and methods. Example: class SUV extends Car { ... }

• Polymorphism: Objects of different classes can be treated as objects of a common supercl...read more

ORM is Object-Relational Mapping, entity class represents a database table, controller layer handles HTTP requests, REST is an architectural style, Spring Boot is a Java framework, Hibernate is an ORM tool.

• ORM (Object-Relational Mapping) is a technique to map objects to database tables and vice versa.

• Entity class represents a database table and its fields as Java objects.

• Controller layer in a web application handles HTTP requests and routes them to appropriate methods.

• REST (R...read more

To connect JDBC with SQL, you need to load the JDBC driver, establish a connection, create a statement, execute the query, and process the results.

• Load the JDBC driver using Class.forName() method

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

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

• Execute the query using statement.executeQuery() method

• Process the results by iterating through the ResultSet object

Swap two numbers without using a third variable in Java

• Use XOR operation to swap two numbers without using a third variable

• Example: int a = 5, b = 10; a = a ^ b; b = a ^ b; a = a ^ b; // Now a = 10, b = 5

Inheritance is a mechanism in which a new class inherits properties and behaviors from an existing class. Polymorphism allows objects of different classes to be treated as objects of a common superclass.

• Inheritance allows for code reusability and promotes the concept of 'is-a' relationship.

• Polymorphism allows for flexibility in code design and enables dynamic method binding.

• Example of inheritance: class Dog extends Animal, inheriting properties and behaviors of Animal class.

• E...read more

An outer join is a type of join operation that includes all rows from both tables being joined, even if there is no match between the rows.

• Includes all rows from both tables, even if there is no match

• Returns NULL values for columns where there is no match

• Types of outer joins include LEFT OUTER JOIN, RIGHT OUTER JOIN, and FULL OUTER JOIN

The question involves answering multiple choice questions and predicting the output of Java code.

• Understand the concepts of Java programming language thoroughly.

• Practice solving MCQs and predicting code outputs to improve accuracy.

• Pay attention to details and syntax in the code snippets provided.

Various tools used in Java development include IDEs, build tools, version control systems, and testing frameworks.

• IDEs: Eclipse, IntelliJ IDEA, NetBeans

• Build tools: Maven, Gradle, Ant

• Version control systems: Git, SVN, Mercurial

• Testing frameworks: JUnit, TestNG, Mockito

Java is a high-level programming language known for its portability, security, and object-oriented features.

• Java is platform-independent, meaning it can run on any device with a Java Virtual Machine (JVM).

• It is known for its strong security features, such as automatic memory management and built-in exception handling.

• Java is an object-oriented language, allowing for the creation of reusable code through classes and objects.

• Popular frameworks and libraries in Java include Spri...read more

Spring is a framework for building Java applications, while Spring Boot is a tool for easily creating stand-alone, production-grade Spring-based applications.

• Spring is a framework that provides comprehensive infrastructure support for developing Java applications.

• Spring Boot is a tool that simplifies the process of creating stand-alone, production-grade Spring-based applications.

• Spring Boot eliminates the need for a lot of configuration, allowing developers to quickly set up ...read more

Exception handling is a mechanism to handle runtime errors in a program to prevent it from crashing.

• It allows the program to gracefully handle unexpected situations.

• Exceptions can be caught and handled using try-catch blocks.

• Common exceptions include NullPointerException, ArrayIndexOutOfBoundsException, and IOException.

• Handling exceptions improves the robustness and reliability of the program.

Use a Set to remove duplicates from an array of strings.

• Create a Set to store unique elements.

• Iterate through the array and add each element to the Set.

• Convert the Set back to an array to get the array without duplicates.

OOPs stands for Object-Oriented Programming. It is a programming paradigm based on the concept of objects.

• OOPs focuses on creating objects that contain data and methods to manipulate that data.

• It involves concepts like inheritance, encapsulation, polymorphism, and abstraction.

• Java is an example of an object-oriented programming language that follows OOPs principles.