TCS Java Developer Interview Questions and Answers

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

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

• When a key-value pair is added, the key is hashed to determine the index in the array where it 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 mult...read more

Java 8 introduced new features like lambda expressions, streams, default methods, and functional interfaces.

• Lambda expressions allow you to write code in a more concise way.

• Streams provide a way to work with sequences of elements.

• Default methods allow interfaces to have method implementations.

• Functional interfaces have a single abstract method and can be used with lambda expressions.

The synchronized keyword in Java is used to control access to shared resources by allowing only one thread to execute a synchronized block of code at a time.

• Synchronized keyword can be used with methods or blocks of code to ensure thread safety.

• It can be used to prevent race conditions and ensure data consistency in multi-threaded applications.

• Example: synchronized void myMethod() { // synchronized method implementatio...read more

Fail fast stops the program immediately upon encountering an error, while failsafe allows the program to continue running despite errors.

• Fail fast: Stops program immediately upon error to prevent further damage. Example: NullPointerException in Java.

• Failsafe: Allows program to continue running despite errors. Example: using try-catch blocks to handle exceptions.

Sort an array and use streams to find names of employees with salary > 50000

• Sort the array using Arrays.sort() method

• Use streams to filter employee objects with salary > 50000

• Map the filtered employee objects to their names

String pool is a memory area in Java heap where unique string literals are stored.

• String pool is a part of Java heap memory where unique string literals are stored.

• String literals are created using double quotes, e.g. "hello".

• Strings created using the same literal will reference the same object in the string pool.

• String pool helps in saving memory by reusing common string literals.

REST is an architectural style for distributed hypermedia systems, while SOAP is a protocol for exchanging structured information in web services.

• REST is lightweight and uses standard HTTP methods like GET, POST, PUT, DELETE, while SOAP uses XML for message format and relies on protocols like HTTP, SMTP, etc.

• REST is stateless, meaning each request from a client to server must contain all the information needed to under...read more

REST state refers to the state of a resource in Representational State Transfer architecture.

• REST state is the current status of a resource in a RESTful system.

• It includes data such as resource attributes, relationships, and links.

• REST state is represented in the form of URIs, HTTP methods, and representations.

• It allows clients to interact with resources by manipulating their state.

• Example: In a RESTful API, the state ...read more

Serialization is the process of converting an object into a stream of bytes to store or transmit it. To stop serialization, mark a field as transient.

• Serialization is used to save the state of an object and recreate it when needed.

• To stop serialization of a field, mark it as transient in the class.

• Example: private transient int sensitiveData;

Failsafe is a mechanism to handle failures without affecting the system's overall functionality, while failfast immediately stops the system upon encountering an error.

• Failsafe is used to ensure that a system remains operational even in the face of failures, by providing alternative paths or fallback options.

• Failfast is a strategy where the system stops as soon as an error is detected, to prevent further damage or inco...read more

A structured approach to connect a controller to a JPA entity in a Java application.

• 1. Create a REST Controller: Define endpoints using @RestController annotation.

• 2. Service Layer: Implement business logic in a service class annotated with @Service.

• 3. Repository Layer: Use Spring Data JPA repository interface for database operations.

• 4. JPA Entity: Define a class annotated with @Entity representing the database table.

• 5....read more

Our project is using JDK 11. We set JDK version in pom.xml. We are using Springboot version 2.5.4. Settings are specified in application.properties. We use Maven as build tool and JUnit for testing.

• JDK 11 is specified in pom.xml file of the project

• Springboot version 2.5.4 is used in the project

• Settings for the project are specified in application.properties file

• Maven is used as the build tool for the project

• JUnit is us...read more

HashMap is non-synchronized and allows null values, while hash table is synchronized and does not allow null values.

• HashMap is non-synchronized and not thread-safe, while hash table is synchronized and thread-safe.

• HashMap allows null values and one null key, while hash table does not allow null keys or values.

• HashMap is generally preferred for non-thread-safe applications, while hash table is used in thread-safe applic...read more

OOP is a programming paradigm based on the concept of objects, which can contain data in the form of fields and code in the form of procedures.

• OOP focuses on creating objects that interact with each other to solve problems.

• Encapsulation: Objects can hide their internal state and require interaction through defined interfaces.

• Inheritance: Objects can inherit attributes and methods from other objects.

• Polymorphism: Object...read more

An interface in programming is a blueprint of a class that defines a set of methods that a class must implement.

• Interfaces in Java are used to achieve abstraction and multiple inheritance.

• Interfaces contain only method signatures, not method bodies.

• Classes can implement multiple interfaces but can only extend one class.

• Example: interface Shape { void draw(); }

• Example: class Circle implements Shape { public void draw() ...read more