45-Day Java Interview Roadmap (0–3 years)

🎯 Goal

• Strong Core Java + DSA basics
• Practical Spring Boot understanding
• Ready for coding + technical interviews

📅 Phase 1 (Day 1–10): Core Java Foundations

🔹 Topics

• Java basics (JVM, JDK, JRE)
• Data types, operators
• OOP (VERY IMPORTANT)
  • Encapsulation
  • Inheritance
  • Polymorphism
  • Abstraction
• Constructors, this, super
• Access modifiers

🔹 Practice

• Write small programs:
  • Bank system
  • Student class
  • Employee management

🔹 Interview Focus

• Difference between:
  • Abstract class vs Interface
  • Method overloading vs overriding

📅 Phase 2 (Day 11–18): Collections + Java Internals

🔹 Topics

• Collections Framework
  • List, Set, Map
• HashMap (VERY IMPORTANT)
• ArrayList vs LinkedList
• Hashing concept

🔹 Must Know

• How HashMap works internally
• Equals & hashCode

🔹 Practice

• Frequency counter
• Remove duplicates
• LRU logic (basic)

📅 Phase 3 (Day 19–25): Multithreading + Java 8

🔹 Topics

• Threads & Lifecycle
• Synchronization
• Executor Service

🔹 Java 8 (Highly asked)

• Lambda expressions
• Streams API
• Functional interfaces

🔹 Practice

• Parallel processing example
• Filter/map using streams

📅 Phase 4 (Day 26–30): JDBC + Exception Handling

🔹 Topics

• JDBC basics (CRUD operations)
• Checked vs Unchecked exceptions
• Custom exceptions

🔹 Practice

• Connect Java with DB
• Insert + fetch data

📅 Phase 5 (Day 31–38): Spring Boot (CRUCIAL for jobs)

🔹 Topics

• Spring Boot basics
• REST APIs
• Dependency Injection
• Annotations:
  • @RestController
  • @Service
  • @Repository

🔹 Build Project

👉 Mini Project:

• User Management API
• CRUD operations
• Connect with DB

📅 Phase 6 (Day 39–45): DSA + Interview Prep

🔹 DSA Topics (Must)

• Arrays
• Strings
• Hashing
• Two pointers
• Sliding window

🔹 Practice Platforms

• LeetCode
• GeeksforGeeks

🔹 Must Solve

• 30–50 problems
• Focus on patterns, not quantity

🧠 Daily Routine (IMPORTANT)

⏰ 3–5 hours/day

• 1 hr → Concept learning
• 2 hr → Coding practice
• 1 hr → Revision / notes

💼 Interview Preparation (Final 5 Days)

🔹 Prepare Answers for:

• Tell me about yourself
• Projects explanation
• Challenges you solved

🔹 Mock Interviews

• Record yourself
• Practice explaining code

🔥 Bonus (Game Changer)

Build 1 Strong Project:

👉 Example:

• Job Portal API
• Interview Experience Portal (your idea 💡)

Stack:

• Java + Spring Boot + MySQL

⚠️ Common Mistakes to Avoid

• ❌ Only watching tutorials (no coding)
• ❌ Ignoring DSA
• ❌ Not revising concepts
• ❌ No project

🎯 Expected Outcome After 45 Days

You’ll be able to:

• Answer Core Java confidently
• Solve easy–medium DSA
• Build & explain Spring Boot project
• Crack 0–3 YOE interviews

45-Day Daily Checklist (0–3 YOE)

📅 Phase 1: Core Java (Day 1–10)

✅ Day 1

• Install JDK, IntelliJ / Eclipse
• Understand JVM, JDK, JRE
• Write first Java program
• Practice: Print patterns, variables

✅ Day 2

• Data types & variables
• Operators (all types)
• Practice: Calculator program

✅ Day 3

• If-else, switch
• Loops (for, while, do-while)
• Practice: Prime number, factorial

✅ Day 4

• OOP: Classes & Objects
• Constructors
• Practice: Student class

✅ Day 5

• Encapsulation
• Getters/Setters
• Practice: Employee class

✅ Day 6

• Inheritance
• super keyword
• Practice: Vehicle → Car

✅ Day 7

• Polymorphism (overloading & overriding)
• Practice examples

✅ Day 8

• Abstraction
• Abstract class vs Interface (IMPORTANT)

✅ Day 9

• Access modifiers
• this keyword
• Practice: Bank system

✅ Day 10

• Revision of OOP
• Interview questions practice
• Write notes

📅 Phase 2: Collections + Internals (Day 11–18)

✅ Day 11

• Collections overview
• List interface

✅ Day 12

• ArrayList vs LinkedList
• Practice: Insert/delete

✅ Day 13

• Set (HashSet, TreeSet)
• Practice: Remove duplicates

✅ Day 14

• Map interface
• HashMap basics

✅ Day 15

• HashMap internal working (VERY IMPORTANT)
• Hashing concept

✅ Day 16

• equals() & hashCode()
• Practice examples

✅ Day 17

• Problem solving:
  • Frequency counter
  • First non-repeating character

✅ Day 18

• LRU Cache basic logic
• Revision + notes

📅 Phase 3: Multithreading + Java 8 (Day 19–25)

✅ Day 19

• Threads basics
• Thread lifecycle

✅ Day 20

• Synchronization
• Race condition

✅ Day 21

• Executor Service
• Thread pool

✅ Day 22

• Lambda expressions

✅ Day 23

• Functional interfaces

✅ Day 24

• Streams API (filter, map, collect)

✅ Day 25

• Practice:
  • Parallel processing
  • Stream problems

📅 Phase 4: JDBC + Exceptions (Day 26–30)

✅ Day 26

• Exception handling basics
• Checked vs unchecked

✅ Day 27

• Custom exceptions

✅ Day 28

• JDBC basics
• DB connection setup

✅ Day 29

• CRUD operations using JDBC

✅ Day 30

• Mini practice:
  • Insert + fetch data
• Revision

📅 Phase 5: Spring Boot (Day 31–38)

✅ Day 31

• Spring Boot intro
• Project setup

✅ Day 32

• REST API basics
• @RestController

✅ Day 33

• Dependency Injection
• @Service, @Repository

✅ Day 34

• Connect with DB (JPA/Hibernate basics)

✅ Day 35

• Build APIs (GET, POST)

✅ Day 36

• Update & Delete APIs

✅ Day 37

• Exception handling in Spring Boot

✅ Day 38

• Finalize User Management API Project
• Test using Postman

📅 Phase 6: DSA + Interview Prep (Day 39–45)

✅ Day 39

• Arrays basics
• Solve 3–4 problems

✅ Day 40

• Strings problems

✅ Day 41

• Hashing problems

✅ Day 42

• Two pointers

✅ Day 43

• Sliding window

✅ Day 44

• Solve 5–7 mixed problems
• Revise all patterns

✅ Day 45

• Mock interview
• Revise Java + Spring Boot
• Prepare HR answers

💼 Final 5 Days (Alongside DSA)

• Tell me about yourself
• Explain your project deeply
• Prepare real-world scenarios
• Practice speaking clearly

🔥 Daily Routine (MANDATORY)

• 1 hr → Learn concept
• 2 hr → Code practice
• 1 hr → Revision

🎯 Execution Rule (MOST IMPORTANT)

Revise EVERY 3rd day ✅

Don’t skip days ❌

Don’t only watch videos ❌

Code EVERY DAY ✅