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Day 30/100

Java, Spring Boot, Microservices, and Angular Interview Preparation Guide 🔥

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List of topics you need to cover if you're preparing for Java Interviews based on current Job market:

1. Core Java Fundamentals (Refer to already posted topics)
2. Advanced Java
- Design Patterns
- Multithreading
- Java Memory Model
- Performance Optimization
- Reflection & Dynamic Proxies
3. Spring Framework
- Spring core concepts
- Spring boot
- Spring Data JPA
- Spring Security
- Spring cloud
- Spring webflux
4. Hibernate
5. Testing (JUnit, Mockito, Integration, Functional, Performance Testing)
6. Build Tools (Maven / Gradle)
7. Logging
8. RDBMS, NoSQL DBs
9. WebSecurity Concepts
10. REST API concepts
11. CI/CD (Jenkins, GitHub Actions)
12. Containerization (Docker, Kubernetes)
13. Version Control (GitHub)
14. Monitoring (Grafana, ELK Stack etc)
15. Cloud (AWS, Azure, GCP (Very rare) )
16. Spring boot microservices
16. Messaging systems
17. Caching Strategies
18. System Design
19. Data Structures
20. Algorithms
21. Agile Methodologies
22. Behavioral questions

Java vs Javascript ✅

✅ Don't Confuse Yourself While Learning Java!

*𝗕𝗮𝘀𝗶𝗰𝘀 𝗼𝗳 𝗝𝗮𝘃𝗮:*
• Java Syntax & Structure
• Data Types & Variables
• Operators
• Control Flow:
- if-else, switch
- for, while, do-while loops
- break & continue
- try-catch-finally
• Methods
• Packages & Imports

*𝗢𝗯𝗷𝗲𝗰𝘁-𝗢𝗿𝗶𝗲𝗻𝘁𝗲𝗱 𝗣𝗿𝗼𝗴𝗿𝗮𝗺𝗺𝗶𝗻𝗴 𝗶𝗻 𝗝𝗮𝘃𝗮:*
• Classes & Objects
• Inheritance
• Polymorphism
• Encapsulation
• Abstraction
• Constructors & Overloading

*𝗝𝗮𝘃𝗮 𝗖𝗼𝗹𝗹𝗲𝗰𝘁𝗶𝗼𝗻𝘀 𝗙𝗿𝗮𝗺𝗲𝘄𝗼𝗿𝗸:*
• List, Set, Map, Queue
• ArrayList, HashSet, HashMap, LinkedList
• Iterators & Loops
• Sorting & Filtering

*𝗘𝘅𝗰𝗲𝗽𝘁𝗶𝗼𝗻 𝗛𝗮𝗻𝗱𝗹𝗶𝗻𝗴:*
• try-catch
• throw, throws
• Custom Exceptions
• Exception Hierarchy

*𝗙𝗶𝗹𝗲 𝗛𝗮𝗻𝗱𝗹𝗶𝗻𝗴 𝗶𝗻 𝗝𝗮𝘃𝗮:*
• Reading/Writing Files
• FileReader & BufferedReader
• FileWriter & BufferedWriter
• Working with JSON & CSV

*𝗝𝗮𝘃𝗮 𝗟𝗶𝗯𝗿𝗮𝗿𝗶𝗲𝘀 & 𝗧𝗼𝗼𝗹𝘀:*
• Apache Commons
• Jackson / Gson for JSON
• JUnit for Testing
• Maven / Gradle

*𝗗𝗮𝘁𝗮 𝗦𝘁𝗿𝘂𝗰𝘁𝘂𝗿𝗲𝘀 𝗶𝗻 𝗝𝗮𝘃𝗮:*
• Arrays
• Strings
• Lists
• Stacks & Queues
• HashMaps
• Trees & Graphs (Basic)

*𝗠𝘂𝗹𝘁𝗶𝘁𝗵𝗿𝗲𝗮𝗱𝗶𝗻𝗴 𝗮𝗻𝗱 𝗖𝗼𝗻𝗰𝘂𝗿𝗿𝗲𝗻𝗰𝘆:*
• Threads & Runnable
• Synchronization
• ExecutorService
• Concurrency Utilities

*𝗔𝗱𝘃𝗮𝗻𝗰𝗲𝗱 𝗧𝗼𝗽𝗶𝗰𝘀:*
• Lambda Expressions
• Streams API
• Functional Interfaces
• Java 8+ Features
• Generics
• Reflection API

💬 Tap ❤️ for more!

Java OOP Concepts Cheat Sheet ☕📘

Master Java’s Object-Oriented pillars:

🔹 Class & Object
🔹 Inheritance
🔹 Polymorphism
🔹 Abstraction
🔹 Encapsulation

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Var Vs let Vs const

Java Developer Interview ❤
It'll gonna be super helpful for YOU

𝗧𝗼𝗽𝗶𝗰 𝟭: 𝗣𝗿𝗼𝗷𝗲𝗰𝘁 𝗳𝗹𝗼𝘄 𝗮𝗻𝗱 𝗮𝗿𝗰𝗵𝗶𝘁𝗲𝗰𝘁𝘂𝗿𝗲
- Please tell me about your project and its architecture, Challenges faced?
- What was your role in the project? Tech Stack of project? why this stack?
- Problem you solved during the project? How collaboration within the team?
- What lessons did you learn from working on this project?
- If you could go back, what would you do differently in this project?

𝗧𝗼𝗽𝗶𝗰 𝟮: 𝗖𝗼𝗿𝗲 𝗝𝗮𝘃𝗮
- String Concepts/Hashcode- Equal Methods
- Immutability
- OOPS concepts
- Serialization
- Collection Framework
- Exception Handling
- Multithreading
- Java Memory Model
- Garbage collection

𝗧𝗼𝗽𝗶𝗰 𝟯: 𝗝𝗮𝘃𝗮-𝟴/𝗝𝗮𝘃𝗮-𝟭𝟭/𝗝𝗮𝘃𝗮𝟭𝟳
- Java 8 features
- Default/Static methods
- Lambda expression
- Functional interfaces
- Optional API
- Stream API
- Pattern matching
- Text block
- Modules

𝗧𝗼𝗽𝗶𝗰 𝟰: 𝗦𝗽𝗿𝗶𝗻𝗴 𝗙𝗿𝗮𝗺𝗲𝘄𝗼𝗿𝗸, 𝗦𝗽𝗿𝗶𝗻𝗴-𝗕𝗼𝗼𝘁, 𝗠𝗶𝗰𝗿𝗼𝘀𝗲𝗿𝘃𝗶𝗰𝗲, 𝗮𝗻𝗱 𝗥𝗲𝘀𝘁 𝗔𝗣𝗜
- Dependency Injection/IOC, Spring MVC
- Configuration, Annotations, CRUD
- Bean, Scopes, Profiles, Bean lifecycle
- App context/Bean context
- AOP, Exception Handler, Control Advice
- Security (JWT, Oauth)
- Actuators
- WebFlux and Mono Framework
- HTTP methods
- JPA
- Microservice concepts
- Spring Cloud

𝗧𝗼𝗽𝗶𝗰 𝟱: 𝗛𝗶𝗯𝗲𝗿𝗻𝗮𝘁𝗲/𝗦𝗽𝗿𝗶𝗻𝗴-𝗱𝗮𝘁𝗮 𝗝𝗽𝗮/𝗗𝗮𝘁𝗮𝗯𝗮𝘀𝗲 (𝗦𝗤𝗟 𝗼𝗿 𝗡𝗼𝗦𝗤𝗟)
- JPA Repositories
- Relationship with Entities
- SQL queries on Employee department
- Queries, Highest Nth salary queries
- Relational and No-Relational DB concepts
- CRUD operations in DB
- Joins, indexing, procs, function

𝗧𝗼𝗽𝗶𝗰 𝟲: 𝗖𝗼𝗱𝗶𝗻𝗴
- DSA Related Questions
- Sorting and searching using Java API.
- Stream API coding Questions

𝗧𝗼𝗽𝗶𝗰 𝟳: 𝗗𝗲𝘃𝗼𝗽𝘀 𝗾𝘂𝗲𝘀𝘁𝗶𝗼𝗻𝘀 𝗼𝗻 𝗱𝗲𝗽𝗹𝗼𝘆𝗺𝗲𝗻𝘁 𝗧𝗼𝗼𝗹𝘀
- These types of topics are mostly asked by managers or leads who are heavily working on it, That's why they may grill you on DevOps/deployment-related tools, You should have an understanding of common tools like Jenkins, Kubernetes, Kafka, Cloud, and all.

𝗧𝗼𝗽𝗶𝗰𝘀 𝟴: 𝗕𝗲𝘀𝘁 𝗽𝗿𝗮𝗰𝘁𝗶𝗰𝗲
- The interviewer always wanted to ask about some design patterns, it may be Normal design patterns like singleton, factory, or observer patterns to know that you can use these in coding.

Make sure to scroll through the above messages 💝 definitely you will get the more interesting things 🤠

All the best 👍👍

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Core Java Notes

𝟴 𝗦𝗸𝗶𝗹𝗹𝘀 𝗧𝗼 𝗠𝗮𝘀𝘁𝗲𝗿 𝗕𝗲𝗳𝗼𝗿𝗲 𝗘𝗻𝘁𝗲𝗿𝗶𝗻𝗴 𝗜𝗻𝘁𝗼 𝟮𝟬𝟮𝟲😍

- Python Programming
- Data Analytics
- ChatGPT
- Data Visualization With Power BI
- Generative AI
- Data Science 
- Tableau
- Java & SQL 
 
𝗦𝘁𝗮𝗿𝘁 𝗡𝗼𝘄👇:-

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Polymorphism in Java

📍 Polymorphism allows a single interface to be used for different types of actions.
📍 It is of two types:

Method Overloading (Compile-time Polymorphism)

Method Overriding (Runtime Polymorphism)


Method Overloading (Same method name, different parameters)

class MathOperations {
int add(int a, int b) {
return a + b;
}

double add(double a, double b) {
return a + b;
}
}

Method Overriding (Same method in parent and child class)

class Animal {
void makeSound() {
System.out.println("Animal makes a sound");
}
}

class Dog extends Animal {
void makeSound() {
System.out.println("Dog barks");
}
}

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Day 31/100

As a Java developer,

Please learn:

1. Core Java Mastery
- OOP principles (SOLID, DRY, KISS)
- Generics, Lambda expressions, Functional interfaces
- Java Streams API (map/reduce, collectors)
- Java Collections framework
- Java Reflection API
- Exception handling

2. Multithreading & Concurrency
- Thread synchronization, Executors, Locks
- Fork/Join framework
- Understanding of race conditions, deadlocks, and thread pools
- Concurrency utilities (java.util.concurrent)

3. Design Patterns & Architecture
- Common design patterns (Singleton, Factory, Builder)
- Architectural patterns (MVC, - Microservices, Event-Driven Architecture)
- Dependency Injection (DI), Inversion of Control (IoC)

4. Java Memory Management
- Garbage Collection (G1, CMS, ZGC)
- JVM heap and stack management
- Profiling tools (JProfiler, VisualVM)
- Analyzing memory leaks, thread dumps, and heap dumps

5. Classloaders and Reflection
- Custom class loaders
- Dynamic class loading
- Reflection for runtime behavior manipulation

6. Spring Framework & Spring Boot
- Spring Core (Dependency Injection, AOP)
- Spring Boot (Auto-configuration, Microservices support)
- Spring Security (OAuth2, JWT)
- Spring Data (JPA, Hibernate integration)
- Spring Cloud (Netflix OSS, Circuit Breakers)

7. Microservices Architecture
- Service discovery (Eureka, Consul)
- Load balancing, distributed tracing, and circuit breaking
- API Gateway (Zuul, NGINX)
- Asynchronous communication with Kafka, RabbitMQ

8. RESTful Web Services
- REST principles, building APIs
- JSON/XML handling
- API versioning, OpenAPI/Swagger documentation

9. Java I/O and NIO
- Blocking vs non-blocking I/O (NIO)
- Asynchronous I/O, channels, selectors
- File handling, serialization and deserialization

10. Reactive Programming
- Project Reactor, RxJava
- Event-driven architecture, backpressure
- Reactive streams, non-blocking IO

11. JPA/Hibernate
- ORM principles, entity relationships
- Lazy vs eager loading
- Caching strategies, query optimization

12. Database Optimization
- SQL optimization, indexing, and transactions
- NoSQL databases (MongoDB, Cassandra)
- ACID principles, CAP theorem

13. Distributed Systems
- Consistency, availability, partitioning (CAP)
- Event sourcing, CQRS (Command Query Responsibility Segregation)
- Distributed caching (Redis, Hazelcast)
- Tools: Apache ZooKeeper, Consul, etcd

14. Testing & TDD/BDD
- Unit testing (JUnit, Mockito)
- Integration and functional testing
- Behavior-driven development (Cucumber)

15. CI/CD & DevOps
- Continuous integration (Jenkins, CircleCI)
- Containerization with Docker
- Orchestration with Kubernetes
- Source control (Git), versioning, branching strategies

16. Performance Tuning & Optimization
- JVM tuning, garbage collection optimization
-Tools for profiling and monitoring (Prometheus, Grafana)

Java Basics every beginner should learn to build a strong foundation:

1. Hello World & Setup

Install JDK and an IDE (like IntelliJ or Eclipse)

Write your first program: public class HelloWorld

2. Data Types & Variables

Primitive types: int, double, char, boolean

Non-primitive types: String, Arrays, Objects

Type casting (implicit & explicit)

3. Operators

Arithmetic: + - * / %

Comparison: == != > < >= <=

Logical: && || !

4. Control Flow

If, else if, else

Switch-case

Loops: for, while, do-while

break and continue

5. Functions (Methods)

Syntax: public static returnType methodName(params)

Method overloading

Return types & parameter passing

6. Object-Oriented Programming (OOP)

Classes & Objects

this keyword

Constructors (default & parameterized)

7. OOP Concepts

Encapsulation (private variables + getters/setters)

Inheritance (extends keyword)

Polymorphism (method overriding)

Abstraction (abstract classes & interfaces)

8. Arrays & ArrayList

Declaring and iterating arrays

ArrayList methods: add, remove, get, size

Multidimensional arrays

9. Exception Handling

Try-catch-finally blocks

throw and throws

Custom exceptions

10. Basic Input/Output

Scanner class for user input

System.out.println() for output

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ENJOY LEARNING 👍👍

30-day roadmap to learn Java up to an intermediate level.

This roadmap is designed for beginners, so adjust your pace as needed.

Week 1: Java Basics
*Day 1-2:*
- Day 1: Get Java installed on your computer and set up your development environment.
- Day 2: Learn about Java's history, its role in programming, and write your first "Hello, World!" program.

*Day 3-4:*
- Day 3: Study Java syntax, data types, and variables.
- Day 4: Understand operators and perform basic arithmetic operations.

*Day 5-7:*
- Day 5: Explore control flow with if-else statements and loops (for and while).
- Day 6: Dive into switch statements and understand how to handle user choices.
- Day 7: Practice writing small programs that use conditions and loops.

Week 2: Functions and Object-Oriented Programming
*Day 8-9:*
- Day 8: Learn about functions (methods) and how to define your own functions in Java.
- Day 9: Study function parameters, return types, and method overloading.

*Day 10-12:*
- Day 10: Understand the basics of object-oriented programming (OOP) in Java.
- Day 11: Learn about classes, objects, and constructors.
- Day 12: Explore encapsulation, inheritance, and polymorphism.

*Day 13-14:*
- Day 13: Study Java packages and access modifiers (public, private, protected).
- Day 14: Practice creating classes and objects in real-world scenarios.

Week 3: Data Structures and Collections
*Day 15-17:*
- Day 15: Dive into arrays in Java and understand their usage.
- Day 16: Study Java's collection framework and ArrayList.
- Day 17: Learn about iterating through collections using loops and iterators.

*Day 18-19:*
- Day 18: Explore other collection types like LinkedList and HashMap.
- Day 19: Understand when to use different collection types in Java.

*Day 20-21:*
- Day 20: Study exception handling in Java and how to deal with errors.
- Day 21: Practice working with try-catch blocks and handling exceptions effectively.

Week 4: Intermediate Topics and Projects
*Day 22-23:*
- Day 22: Study file handling in Java, including reading and writing files.
- Day 23: Create a small project that involves file operations.

*Day 24-26:*
- Day 24: Learn about multithreading and how to create and manage threads in Java.
- Day 25: Study Java's built-in libraries for networking and socket programming.
- Day 26: Work on a project that involves multithreading or networking.

*Day 27-28:*
- Day 27: Explore more advanced Java topics like JavaFX for GUI development or JDBC for database connectivity.
- Day 28: Work on a more complex project that combines your knowledge from the past weeks.

*Day 29-30:*
- Day 29: Review and revisit any topics you found challenging.
- Day 30: Continue building projects and exploring areas of Java that interest you.

Consider joining Java communities and forums to seek help and advice. Java is a versatile language with many applications, so your learning journey can continue well beyond this roadmap. Good luck!

✅ 50 Must-Know Java Concepts for Interviews ☕💡

📍 Java Basics
1. What is Java?
2. JVM, JRE, JDK — know their roles and differences
3. Data Types & Variables — primitives, reference types
4. Operators — arithmetic, relational, logical
5. Type Casting — implicit and explicit

📍 Control Flow
6. if-else statements
7. switch-case syntax and use-cases
8. Loops: for, while, do-while
9. break & continue — control loop behavior
10. Ternary operator (?:) — compact conditional

📍 OOP Concepts
11. Class & Object — blueprint and instances
12. Inheritance — code reuse and is-a relationship
13. Polymorphism — compile-time (overloading) & runtime (overriding)
14. Abstraction — hiding implementation details
15. Encapsulation — data hiding with access modifiers

📍 Core OOP in Java
16. Method Overloading — same method name, different params
17. Method Overriding — subclass modifies superclass method
18. Constructors & Constructor Overloading
19. this and super keywords — referencing current and parent class
20. Static keyword — class-level variables and methods

📍 Exception Handling
21. try-catch-finally blocks
22. throw vs throws — raising vs declaring exceptions
23. Checked vs Unchecked Exceptions
24. Custom Exceptions — user-defined error handling
25. Common exceptions like NullPointerException, ArrayIndexOutOfBoundsException

📍 Collections Framework
26. List, Set, Map interfaces
27. ArrayList vs LinkedList — pros & cons
28. HashSet vs TreeSet — unordered vs sorted sets
29. HashMap vs TreeMap — unordered vs sorted maps
30. Iterator & enhanced for-loop for traversing collections

📍 Strings & Arrays
31. String vs StringBuilder vs StringBuffer — immutability and performance
32. Common String methods (substring, equals, indexOf)
33. 1D & 2D Arrays — declaration and traversal
34. Array vs ArrayList — fixed vs dynamic size
35. String immutability — benefits and implications

📍 Advanced Java
36. Interfaces & Abstract Classes — design contracts and partial implementation
37. Lambda Expressions — functional programming style
38. Functional Interfaces — single abstract method interfaces
39. Streams API — processing collections declaratively
40. File I/O with FileReader, BufferedReader

📍 Multithreading & Concurrency
41. Thread class vs Runnable interface
42. Thread Lifecycle (New, Runnable, Running, Waiting, Terminated)
43. Synchronization — thread safety techniques
44. wait(), notify(), notifyAll() — inter-thread communication
45. Executor Framework — managing thread pools

📍 Best Practices & Tools
46. Writing Clean Code — naming, formatting, SOLID principles
47. Java Memory Model — Heap vs Stack
48. Garbage Collection basics — automatic memory management
49. Unit Testing with JUnit
50. Version Control — Git & GitHub basics

💡 Pro Tip: Understand these concepts well, back answers with code examples, and relate them to real projects in interviews.

❤️ Tap ❤️ if you found this helpful!